Force Rhubarb Indoors
Force rhubarb indoors and harvest tender, pink rhubarb mid-winter while the snow flies outdoors.
By Steven Biggs
Force Rhubarb Indoors for a Mid-Winter Harvest
Rhubarb and candles?
One day I got chatting with my neighbour’s fence installer, who was interested in my garden.
I was picking rhubarb as we spoke, so I mentioned that I also force rhubarb in my basement over the winter.
That’s what got us on the topic of candles.
He was from Yorkshire, England, an area that once produced 90 per cent of the world’s forced rhubarb. He explained that the tradition there is to tend and harvest the crop, grown in big, dark sheds, by candlelight.
After we chatted I went online to see pictures of Yorkshire forced rhubarb. It’s beautiful! The long stems are bright red, and they’re topped with small yellow leaves. Farmers grow this forced rhubarb in the dark to get very long, tender stems. A small amount of light can change the way the rhubarb grows, but because the candles give a faint light, they don’t affect growth.
It’s easy for home gardeners to force rhubarb over the winter too. (You can opt out of using a candle if its’ not your style! I don’t use one.)
My winter-forced rhubarb. Not quite as nice as what they grow in Yorkshire, but still a nice winter treat.
How Forcing Rhubarb Works
Let’s back up to get a handle on what we’re doing. When we force rhubarb indoors over the winter, we’re tricking a dormant rhubarb root into thinking it’s spring.
We trick it by putting it somewhere warm.
That warmth stimulates growth.
If you’ve ever grown plants in conditions where there’s not enough light, you’ll know that they get lanky, with long stems.
The rhubarb sends up long stems too, and the leaves stay quite small while there’s no light.
If there’s light, upward growth slows, and stems and leaves develop a green colour from photosynthesis. It doesn’t take a lot of light to change the growth. Hence the candles.
Rhubarb grown in the garden is more green and fibrous than forced rhubarb.
Why Force Rhubarb Indoors
What makes forced rhubarb special is that by excluding light, we get very long, tender stalks with a sweeter, milder flavour than rhubarb grown in the garden.
(Intrigued by the idea of excluding light to change quality? Here’s a fun article about blanching veg.)
Forced and outdoor-grown rhubarb are two very different things. The former has a delicate flavour and beautiful colour. The latter is greener and more fibrous.
Fresh forced rhubarb is a nice addition to the menu over the winter.
There’s one other reason to consider forcing your own rhubarb: It fits in nicely with rhubarb patch care.
In the right location, a patch of rhubarb grows larger each year. When a clump of rhubarb is well established and thriving, you simply “harvest” some of it in the fall by dividing the clump once the leaves have died back and it is dormant. Like plants in a perennial flower garden, dividing and bringing in fresh soil and compost is a good practice to keep a rhubarb patch thriving. As you divide the rhubarb patch, keep the hunk of root that you dig out for forcing.
Steps to Forcing Rhubarb Indoors
In the Summer
When conditions are good, a rhubarb patch gets larger every year. Don’t dig anything yet, but select a part of your patch that you can “harvest” for indoor forcing once the patch is dormant in the fall.
In the Fall
When you divide your clump of rhubarb in the fall, you get roots that you can force indoors over the winter.
The rhubarb should be dormant before you dig out a piece for winter forcing. Wait until the leaves have died back before digging. (But do it before the ground freezes!)
Then harvest the part of your rhubarb patch that you chose during the summer. Rhubarb crowns are woody, so you’ll need a spade to chop down into it.
Pot up the dormant root. Some years I pot the roots into recycling bins. Some years into large black nursery pots. Crates might work well too. Just like a houseplant, you want excess water to be able to drain from the bottom. (Also think about what to put underneath the potted rhubarb root if you don’t want water on the basement floor.)
Once the rhubarb root is potted up, store it somewhere cool until it’s time to force it. I put mine in my garage until mid-winter, when I’m ready to bring it in the house to force it. The roots are very cold tolerant, so if your storage area freezes, that’s fine.
There’s no rush to bring the dormant rhubarb root indoors. Let the root remain dormant and at a cool temperature for a few weeks.
Where to Force Rhubarb Indoors
In a previous house I forced rhubarb in the cold cellar under the stairs.
The rhubarb will grow when it is placed somewhere warm. Remember, you’re simply tricking the plant—making it think spring has arrived.
In a previous house, I put the rhubarb in a dark cold cellar under the stairs.
In my current house, I put the rhubarb in my furnace room.
Taking Care of Forced Rhubarb
Care is simple: Just water the soil as it starts to get dry. It should be moist, not wet.
Don’t feed the plant. It is using energy stored in the thick, fleshy roots.
Supplies to Force Rhubarb Indoors
A container to pot up the dormant rhubarb root
Potting soil
Candle (optional!)
Harvesting Forced Rhubarb
Harvest stalks when long enough to use. How big they get will depend on how much root you dug out, and how much energy was stored in that root.
Repeat a few times.
You’ll find that the longer you leave the forced rhubarb root to produce stalks in the dark, the skinnier and skinnier the stalks become. That’s because as the plant continues to send up stalks in the dark, it’s using up its stored energy.
(I find I get about three harvests before stem size gets too skinny to make it worthwhile harvesting.)
When you find the stalks are very skinny and no longer worth harvesting, you can move the plant to the light to just let it grow. Or, if you don’t have space, put it back into your cold-storage space until spring.
Grow a Container Vegetable Garden
And get an early harvest of crops that usually take too long!
Force Rhubarb Outdoors
By the time spring arrives, your winter-forced rhubarb root will be done producing rhubarb.
But you can also force some of your in-ground rhubarb plants. Again, it’s a combination of darkness and extra heat that gives you long, tender stalks.
You do this spring forcing right in the patch, without disturbing the plant.
Here’s what to do:
A rhubarb forcer, a purpose-made terracotta pot with a removeable lid for forcing rhubarb.
As you see buds start to swell on the crown, cover a part of the patch with a large inverted pot or garbage can. (To exclude the light and get nice, pink stalks, cover the drainage holes of the pot to keep out light)
You can insulate the sides of pots with leaves or straw if you want to speed up the process by making it warmer inside
Pick once the stalks reach the top of the pot
Give the roots you forced “time off” over the summer to recharge – don’t pick from them
There are also purpose-made terracotta rhubarb forcing pots. They’re beautiful, but I’ve never seen them for sale here in Ontario. And I suspect that if I found them, they’d cost and arm and a leg.
Supplies to Force Rhubarb Outdoors
Healthy, established rhubarb plant
Large pot
Tape to cover holes in the pot
Straw or leaves to insulate the outside of the pot
Rhubarb Forcing FAQ
What if my indoor forcing area has some light in it?
If there is enough light, you will not get the elongated, bright red stalks. Instead the plant will produce more compact stalks with some green chlorophyll in them. Not the end of the world…but you can get green stalks all summer. So create a dark space using a curtain or tarp.
Why are my forced rhubarb stalks smaller than the ones I see at the grocery store?
Commercial growers will often let rhubarb plants grow two or three years without harvesting any stalks before using the root for forcing. That means the root has a lot of stored up energy. In a small home garden, where the gardener is forcing roots that have been harvested from, there won’t be as much stored energy.
What should I do with the rhubarb plant after forcing?
Commercial growers often discard roots that they’ve forced. But you can plant the spent rhubarb root in your garden or share it with a neighbour. But don’t harvest from it for a couple years – allow the plant to recover and store energy.
I just planted my rhubarb. Can I force it?
No. There won’t be enough stored energy in the root to give you good results…and if it’s a small plant, you might kill it. Commercial growers often grow plants in the field without harvesting anything for two or three years to allow the plants to store up energy before forcing.
What about bugs?
Because the potted roots were harvested in cold temperatures, and then stored somewhere cold, don’t worry about bugs.
What’s a rhubarb stick?
Some people refer to rhubarb stalks as “sticks.”
More on Rhubarb
Ontario Farmer Brian French forces 10,000 square feet of rhubarb over the winter.
Hear how he forces rhubarb, and find out his rhubarb-growing tips.
Want More Ideas?
Guide to Blanching in the Vegetable Garden
How to Blanch Celery, Cauliflower, and Other Vegetables. Blanching in the garden refers to covering up part of all of a plant to exclude light.
By Steven Biggs
How to Blanch Celery, Cauliflower, and Other Vegetables
One word, two meanings!
For many people, blanching vegetables means a quick dip in boiling water before freezing them. This type of blanching slows down or stops the enzymes that cause colour and flavour loss.
But there’s another type of blanching, and it’s something that we do right in the garden.
Blanching in the garden refers to covering up part of all of a plant to exclude light. Without light, it grows differently.
The result is a milder tasting and more tender crop.
Keep reading to find out what crops you can blanch—and how to do it.
Common Crops
These are crops that are commonly blanched in the garden. You can grow them without blanching, but blanching improves the quality.
Asparagus
Cardoon
Cauliflower
Celery
Endive and Escarole
Leek
Rhubarb
Different Ways to Blanch
Soil hilled up along a row of leek plants.
Depending on what you’re growing, and how you want to grow it, there are a few ways to blanch vegetables in the garden.
Remember, blanching just means excluding sunlight. Here are some ways to do it:
Cover the plant (e.g. inverted pots)
Hill the plant with soil
Wrap something around the plant (e.g. cardboard or newspaper)
How Long?
The plants are blanched for a few days to weeks before harvest – not the entire life of the plant.
Crop Blanching Tips
Asparagus
If you’ve ever seen white asparagus, these are spears that have been blanched by hilling with soil. It’s a delicacy in Europe, less common in North America.
Cardoon
Blanching cardoon plants by wrapping them in fabric.
I’ve heard of people growing cardoon in a trench…but it’s a pretty big plant needing a pretty big trench. Instead, wrap mature plants 2-3 weeks before harvest, leaving the top of the older leaves exposed, but the base covered. The idea is that the inner leaves are white and tender. Some people use cardboard, but I think the most elegant cardoon blanching I’ve seen was burlap coffee sacks.
Cauliflower
With cauliflower we blanch the head. White-headed cauliflower is blanched to keep it bright white. It is still edible if you don’t blanch it…but can develop a yellow or green tinge, and get a stronger flavour.
Blanching cauliflower by tying together leaves to cover the head.
As the developing heads begin to expand, tie leaves around them to keep out the light. Don’t wrap the leaves too tightly over the small head as it will need space to expand. I’ve heard of people using paper bags, but if there are leaves there, it’s easier and less wasteful.
There are also “self-blanching” types of cauliflower, with leaves that naturally grow around the developing head. Some of these varieties still benefit from additional wrapping.
Celery
With celery we blanch stalks for 2-3 weeks leading up to harvest, keeping the leaves at the top exposed. Blanching helps reduce bitterness and lighten the stalk colour.
Blanching celery with waxed milk cartons that have the top and bottom cut out.
As with cauliflower, there are also “self-blanching” celery types. These have a lighter colour and milder flavour.
Hilling soil around the stalks is one way to blanch celery. Grow celery in a trench, and then gradually fill in the trench with soil leading up to harvest. If you use soil, first wrap the stalks with newspaper, so you don’t get lots of soil between the stalks.
You can also blanch celery by tying paper around the stalks, covering with waxed cardboard milk cartons or tall narrow tins that have both ends removed, or surround the stalks with boards.
Blanching celery plants with boards.
Grow a Container Vegetable Garden
And get an early harvest of crops that usually take too long!
Endive and Escarole
A board propped up over a row of endive or escarole is an easy way to blanch it.
Many people grow endive and escarole for the bitter taste. But you can blanch them to reduce the bitterness. Cover entire plants for a week before harvesting.
For individual plants, cover with a clay pot or a paper bag. For a whole row of plants, place a board over the row.
Leek
The base of leek plants can be blanched to give tender white flesh. In late summer, hill the base of the plant with soil, or wrap to exclude light. As with celery, leeks can also be grown in a trench that is gradually filled in as the plant gets taller.
Rhubarb
Blanch rhubarb by cover up plants with an inverted bushel basket as they begin to grow in spring.
When rhubarb is blanched it produces tender, elongated stalks that have a bright pink-red colour.
To blanch rhubarb, put an inverted bushel basket over the plant in the spring, as it begins to grow.
Why Not Blanche a Weed!
While a weed for many, dandelions are a kitchen staple for others. Our springtime menu includes dandelion frittata or a mixed salad with dandelion leaf pieces.
But dandelion, like its kin in the chicory clan, can be very bitter. The solution is to blanch dandelion. Simply cover with an inverted clay pot or a board – and you’ll be rewarded with tender, translucent, and mild-tasting leaves.
Blanching Challenges
Blanch dandelion by covering with an inverted pot or a board.
Blanching is easy to do. The biggest challenge is remembering to do it in time.
Another challenge is lightweight covers that blow away on windy days. If you use terracotta pots, they’re heavy enough to stay in place. But plastic coverings can blow away. The solution is to weigh them down with a brick or rock.
Top Blanching Tip
Put a note on your calendar to remind you to blanch your crops ahead of time.
Garden Blanching FAQ
Is Blanching Optional?
You don’t have to blanch these vegetables to eat them. But blanching gives a milder tasting, more tender, and more attractive vegetable.
What is “Self-Blanching?”
Some varieties don’t need help from gardeners with blanching. For example, with cauliflower, self-blanching varieties have leaves that grow to cover the head. Self-blanching celery has stalks with a mild flavour that don’t require blanching.
Why Grow Varieties that are not Self-Blanching?
You might be wondering why bother growing varieties that need blanching when self-blanching varieties are available. As you choose varieties, self-blanching is one trait to consider, along with other things such as having different harvest windows, price, and availability.
Looking for More Ideas?
Gardening Courses
Grow Vegetables in Straw Bales
Straw bale vegetable gardening is an easy way to create more growing space.
By Steven Biggs
Make More Growing Space with Straw Bale Gardens
I started straw bale gardening to solve a problem.
The problem? We needed more growing space for my daughter Emma’s 100-plus tomato varieties.
We have a big yard for the city. But there’s a black walnut tree that makes much of the yard unsuited to growing tomatoes.
(That’s because black walnuts give off a compound that kills the tomato plants…and a number of other plants too.)
With a long and ugly driveway that could fit a couple of school buses, Emma and I began to imagine a tomato plantation on the driveway.
In this post I’ll talk about how to use straw bales to make gardens on paved areas or over soil that’s not great for gardening.
Straw Bale Driveway Garden
Straw bales are an easy way to create a near-instant garden on paved surfaces and areas with poor soil. That’s because the straw bale is both the growing medium and the container.
Here’s how it works: As the straw bale decomposes, it creates an ideal growing medium that is well aerated and holds lots of moisture. It’s like a big sponge. It’s perfect for plant roots – better than many garden and container soils.
In short, you’re composting a bale of straw, and growing your vegetable plants in it at the same time.
Straw Bale Gardening: Top Tip
Our straw bale driveway garden
The most important thing to remember is that bales should be “conditioned” before you grow in them.
Conditioning means kick starting the microbial action. And you know when it’s working because as the microbes start to break down the straw, the temperature inside the bale goes up. We don’t plant in it yet…it might be too warm for our plants.
As the temperature comes down, your bale is ready to plant. Some people use a thermometer. I stick in my finger. It’s not an exact thing.
I allow 3-4 weeks for this conditioning process. It might be less if you’re somewhere warmer than me.
Since the bales in our driveway garden are for heat-loving tomato plants that we put out in late May, we start conditioning the bales late-April to make sure they’re ready for the planting date. I just work back four weeks from my planting date.
Straw Bale Garden Setup
Emma conditioning the newly arrived straw bales.
Before your bales become heavy from watering them, it’s a good time to think about how you want to arrange them. There’s no right or wrong, it depends on your situation:
If you’re planning to use a long soaker hose, you might want them in a long line.
If you’re gardening with kids, arranging them in a square makes for a nice hidoute once the plants get bigger
If you’re watering with a hose, arrange the bales so you can easily move amongst the bales with the hose
How to Orient Straw Bales
Once you know how you want to arrange the bales, think about how you’re orienting them. You can place them so that the loops of twine are on the top and bottom – or the twine is at the sides. Both ways of orienting the bales are fine.
But here’s how I do it: When positioned so that the twine is at the sides, the straw within is mainly oriented vertically. Bales positioned this way absorb more water, so it’s less likely to run off of the side of the bale.
How to Condition Straw Bales
To condition the bales – which just means getting the microbes working – we need 2 things:
Water
Nitrogen
In this picture the bales are oriented with the twine at the top and bottom of the bales. We now prefer to have the twine at the side for easier water penetration.
Place a nitrogen source on top of the bales and water well. The goal is for the water to soak into the bale and move some of the nitrogen into the bale. Use a low pressure and volume so that water doesn’t flow over the sides of the bale (and take the nitrogen with it).
More on the nitrogen source: When you’re looking at the numbers in the fertilizer formulation, you want the first number, the nitrogen, to be higher than the others. For example, blood meal is 12-0-0. That’s what I usually use.
Other years I’ve also used a high-nitrogen organic fertilizer derived from guano, and a lawn fertilizer.
Here’s how I condition straw bales with blood meal:
I water well every day for the first week.
Starting on the first day, and again every other day, I put a 2 cups of blood meal on the bale BEFORE watering (so the water moves some of the blood meal into the bale).
I give 3 applications of blood meal.
As we get into week 2, the bale should be warming up nicely inside!
After 2 weeks, fertilize the bales with a balanced, all-purpose fertilizer.
During this conditioning process, the temperature can go up to about 50°C (120°F), and then it drops. You can plant in the straw bales once the temperature has dropped below about 26°C (80°F)
Grow a Container Vegetable Garden
And get an early harvest of crops that usually take too long!
Straw-bale Garden Plant Layout
Plant densely to make the best use of space in your straw bale garden.
Wondering about plant spacing in a straw-bale garden? Because a well-managed straw bale garden provides plants lots of moisture and an excellent growing medium, you can plant densely.
We aim for two or three tomato plants per bale. Around those tomatoes we sow bush beans and leafy greens.
Something else to think about with straw bales is that you can plant into the side of the bale too. We’ve grown dwarf tomato plants out the side of bales, while at the top are normal determinate and indeterminate varieties.
How to Support Plants in Straw Bale Gardens
Because there is a paved surface below, and because the bales decompose and start to collapse over the summer, regular staking is not an option.
Here’s what I do instead of staking:
Use 3-4 stakes positioned over the bale to create a self-supporting tee-pee.
Put the bales next to a fence and grow vining crops up the fence.
Looking for tomato-staking ideas? Find out how to stake and support tomato plants.
Straw Bale Garden Planting and Care
How to Plant in Straw Bales
When I show pictures of straw bale gardens to groups, I’m asked where the soil is. There doesn’t have to be soil, because the straw is the growing medium.
When transplanting, use a trowel to pry an opening into the bale. Then place the transplant into the opening, and close up the opening. Be sure to cover the transplant roots with straw so they remain moist.
With large seeds like beans, we just insert them right into the bale. Again, no soil necessary.
When direct seeding smaller seeds onto a straw bale, a thin layer of soil is helpful. We add about an inch of soil over the top of the bale if we’re seeding leafy greens. Use a potting soil or good garden soil that won’t cake with frequent watering.
Straw Bale Garden Fertilizer and Water
Once your bales are conditioned and planted, feed with a balanced, all-purpose feed and keep them well watered. Because the inside of the bale remains well aerated, excess water is not likely to harm the plants. But excess water will wash away nutrients.
If there are not many bales in your garden, hand watering might be fine.
For larger gardens, drip irrigation or a soaker hose works well. Position the soaker hose to sprays downwards, into the bale.
Grasses and Mushrooms on Straw Bales
It’s normal to get mushrooms growing on straw bales. It means you’ve created good growing condtions.
Don’t be surprised to see little grass-like plants and mushrooms growing on the bales. These are good – it means you’ve created good growing conditions.
The grasses are any residual grain within the bale that germinates and grows. They won’t out-compete your crops. Just pull them off.
Straw Bale FAQ
What do you do with Straw Bales After Harvest?
After a year of growing I use the straw to mulch gardens, on pathways, and in my compost pile.
How Many Years do Straw Bales Last?
I’ve sometimes used bales a second year. How fast a bale decomposes varies with your weather conditions. Friends in warmer areas report that one year is the maximum for them.
What if the Twine Breaks?
Broken bales? No problem. In this straw bale garden the tall sections are tomato cages filled with loose straw from broken bales.
If possible, tie it back together; or use a new, longer piece of twine to tie together the bale. If that doesn’t work, you can pack straw into a cage or pot instead.
As you carry the straw bales, try to do it in such a way that the twine does not slide off the side of the bale.
Do Straw Bales Leave Marks?
Yes. Straw bales can darken paved surfaces.
I don’t recommend using them on wood because it creates conditions that could speed up the decay of the wood.
One year I had them against a board fence, and it resulted in dark marks on the fence – so I now position the bales a couple of inches away from the fence.
What About Hay Bales?
Hay bales can also make an excellent growing medium, but there are a couple of reasons they’re not used as frequently as straw bales:
Hay often includes lots of grass seed – not something you want to introduce to your garden
Hay is often more expensive than straw
What are the Best Plants for the Straw-Bale Gardening method?
You can grow a wide range of vegetable crops in straw bales.
Heat-loving crops benefit from the warm root zone in the bales
Root crops develop very well in the well-aerated growing medium
Leafy greens grow well and can be planted underneath other crops such as tomatoes
Cascading plants such as nasturtiums (for edible flowers!) can drape down over the side of the bales
Where can I Buy Straw Bales?
Straw bales are fun for kids.
I used to bring home loads of bales in my minivan. And my family hated all the prickly little bits of straw it left everywhere. So now I just get straw delivered.
To find a farmer, use an online classified advertising website.
And if you have kids: Get straw bales earlier than you need them – for your kids. Straw bales are like giant, biodegradable Lego blocks.
Don’t Straw Bales attract Rats?
The mention of straw has some people wondering whether straw bale gardens will be overrun with rats.
It’s a good question. Not in my experience.
The thing to remember with rats and mice is that they’re looking for food, shelter, and water.
A bale on a paved surface doesn’t give them burrowing room. Doesn’t give them water. Doesn’t give them much food.
What’s more likely to attract rats is bird baths, bird feeders, leaving out pet food, and improperly stored garbage. (On that note, gardening itself, and growing plants with seeds and fruit that are food for rodents, attracts rats.) Remember too, that they’re already abundant in many areas – just not out and about at times that we see them.
More Vegetable Garden Techniques
How to Grow Kohlrabi
How to grow kohlrabi.
By Steven Biggs
Growing Kohlrabi in Home Gardens
THREE CHEERS for one of the most photogenic veggies out there.
To my kids, kohlrabi looked like flying saucers. When I look at kohlrabi from the right angle I see a person having a bad hair day.
Whatever your imagination paints it as, it’s both attractive and unusual, making it a nice fit for an ornamental edible garden.
It’s also easy to grow, quick to mature, and versatile in the kitchen.
If you haven’t tasted it before, I’d describe the flavour as a cross between a mild apple and mild turnip. Let’s call it turnip light!
In this post I’ll talk about how to grow kohlrabi and how to fit it into your garden.
It Starts as a Rosette
Kohlrabi is a member of the cabbage clan. It has an edible stem that fattens up right above the soil level. Before the stem plumps up, though, the plant is a rosette of leaves. As the stem thickens, the symmetry of that rosette remains, with leaves projecting out from the bulb-like stem.
Top Tip for Kohlrabi Success
Here’s the key to your kohlrabi success: Fast, uninterrupted growth.
To get that type of growth, grow the plant in well-fed soil, with cool temperatures and consistent moisture.
Site
Kohlrabi is an easy-to-grow vegetable that is versatile in the kitchen.
Like its cabbage cousins, kohlrabi grows best in soil with lots of organic matter
A spot with full sun is best (although I’ve had decent results growing kohlrabi in partial shade)
Grow Kohlrabi from Seed
Kohlrabi is easy to grow from seed, indoors or outdoors. I don’t usually bother starting them indoors in the spring, but it’s an option if you want the earliest possible harvest. If you start them indoors, there’s no need for a heat mat.
Sow seeds approximately 5 mm (1/4”) deep
Outdoors: Start sowing about 1 month before the last spring frost
Indoors: Start kohlrabi transplants about 1 month before you plant to move them to the garden
Here are a couple of ways to get a longer kohlrabi harvest:
Start additional seeds every 2-3 weeks
Grow more than one variety, choosing varieties that take different amounts of time to mature
A young kohlrabi plant, before the stem has started to fatten up.
Note: While kohlrabi plants are tolerant of cold weather, a hard freeze can cause young plants to bolt – to jump right to the flowering stage. That would mean no thick edible stem. So there’s a limit to how early you can plant them out.
Kohlrabi as a Summer Succession Crop
When kohlrabi is a succession crop, I like to pre-start seedlings indoors (or outdoors, in another part of the garden). That way, I have transplants ready to go once the desired space opens up.
While I rarely start spring kohlrabi indoors in the spring, I find it’s the best way for me to grow kohlrabi for summer succession because:
It allows me to have a tighter succession...with larger plants ready as soon as the space is open
The hot, dry summer weather that I get here is not ideal for outdoor seeding
Note: Depending on growing conditions in your area – and how much attention you give your garden over the summer – kohlrabi might or might not be a suitable summer succession crop. Dry conditions can cause erratic growth and give a woody texture with a strong, bitter flavour.
Grow a Container Vegetable Garden
And get an early harvest of crops that usually take too long!
Spacing
Thin kohlrabi plants to give a spacing of approximately 10-15 cm (4-6”) apart.
With direct-seeded kohlrabi, I usually plant them more densely than recommended. Then I thin out the row as the stems begin to fatten, enjoying an early harvest of young kohlrabi.
Kohlrabi leaves are edible, so if I thin out any plants before the stems enlarge, I can still add the leaves to a salad!
Planting more densely is also cheap insurance against losses and poor germination.
If you’re aiming to grow larger kohlrabi, increase the spacing a bit – and look for a variety know for size.
Sow the seeds approximately 5 cm (2“) apart
Thin to 10 – 15 cm (4-6”) apart
Space rows 30cm (12”) apart
If you’re aiming to grow larger kohlrabi, increase the spacing a bit – and look for a variety know for size.
Challenges
I find the early crop is not bothered much by pests. But later sowings and summer-succession transplants are growing when there are more pest pressures in the garden. That means young seedlings can be vulnerable to flea beetles, cabbage worm, and cabbage looper. An easy solution is to cover young plants with a floating row cover.
Where possible, rotate crops to minimize pest and disease pressures. That means it’s best not to plant kohlrabi where you’ve had you’ve had related crops (broccoli, cauliflower, collards, kale, turnip, rutabaga, cabbage, bok choy, Brussels sprouts, and mustards) in last 4 years.
Harvest and Storage
Kohlrabi usually take a couple of months to mature. Pick when they’re anywhere between the size of a golf ball and a tennis balls. Remember: smaller will be more tender.
Kohlrabi is frost hardy, so there is no rush to harvest it in the fall.
In the Kitchen
Kohlrabi is versatile in the kitchen.
You can eat kohlrabi raw or cooked. Either way, peel it first, because the skin can be tough. I prefer to use a paring knife (sometimes a potato peeler gets stuck on the spots where the leaf joined the stem.)
Here are some ways I’ve enjoyed serving kohlrabi:
Sliced, on a veggie platter
Grated, in slaws and salads
Poached (in white wine with butter is nice!)
Cut into ribbons, and added to a stir fry
Cubed and added to curries
Remember: The young leaves and leaf stalks are edible too!
Ornamental Vegetables for Fall
By Steven Biggs
Vegetable Crops That Look Great in the Fall
As I write this, it’s spring. But I’m picturing my fall garden.
I was just scouting out the spot where my Swiss chard will go this year.
I always fit in chard close to my kitchen window.
An Ornamental Edible
In the garden outside my kitchen window I weave together the ornamental and the edible. I especially treasure edible plants with ornamental appeal.
And that’s where chard fits in.
Swiss chard paints this part of my garden in yellows, reds, pink, and orange.
As cool, grey fall weather arrives, Swiss chard is a bright spot in a fading garden.
Summer-Long Production
Leafy greens like lettuce, spinach, and arugula come and go with summer heat.
They bolt
They get leathery
They get bitter
But Swiss chard sails through the heat with a prodigious output of tender leaves.
A Long-Lasting Edible
Swiss chard paints this part of my garden in yellows, reds, pink, and orange.
As cool, grey fall weather arrives, Swiss chard is a bright spot in a fading garden.
It shines.
When frost renders swathes of the garden a wilted green-brown, chard still shines. The bright leaves bow to the frost, then spring back up as sunshine warms them.
It perseveres until a hard freeze.
Put Chard Where You Can See it in the Fall
I’m picturing the spot where my chard will go, and making sure it’s somewhere I can enjoy looking at it from my kitchen window through the fall.
More Ornamental Vegetables for the Fall Garden
Cardoon is another ornamental vegetable that looks great in the fall. Find out more about cardoon.
Artichokes hold up nicely in fall weather. Find out how to grow artichoke.
Home Garden Soil Contamination
By Steven Biggs
Understanding the Risk of Soil Contamination Around Your Home
AFTER MOVING INTO MY WORLD WAR I-ERA HOUSE, I decided to find out if the paint-chip-studded soil next to the house was safe for growing edible crops.
Many pre-1991 paints contained lead, and those that are pre-1960s—particularly exterior paints—are thought to be the worst culprits.
Lead was also used as a gasoline additive into the 1990s. So urban areas with older buildings, where there have been years of car exhaust—and maybe even industrial emissions—tend to have higher soil lead levels than rural, agricultural areas.
With this in mind, I wanted to understand what, if any, risk lay hidden in my soil.
If you’ve wondered what, if anything, to check with the soil in your garden, keep reading for a practical way to approach soil contamination.
Conflicting Information
With an older house, I was worried about lead contamination from paint.
The more I delved into the question of urban soil contamination, the less clear the issue became.
I found a government fact sheet saying there was minimal risk to consuming veggies grown in soil with lead levels below 200 parts per million (ppm)
But one from another jurisdiction advising 300 ppm.
Both noted increased risk for children (think soil moving hand to mouth), in which case one gave a safe upper limit of 100 ppm.
I was left wondering whether I should go with 100, 200 or 300 ppm.
So I Got on the Phone
When I called Ontario’s Ministry of the Environment, I was told that contaminant levels in typical agricultural soil are often less than urban areas, but there should be no concern as long as the readings for my soil fell below the residential standards, as set out in the provincial Environmental Protection Act.
But…I should also keep in mind that a reading above that residential level isn’t necessarily unsafe.
Understanding soil contamination was starting to seem as fun as doing my tax return.
So, after scanning the Act, I added 45 ppm lead (for typical agricultural soil), 120 ppm lead (for residential standards), and a big question mark (for “isn’t necessarily unsafe”) to my growing list of values.
This was getting to be as much fun as preparing a tax return!
And just as filling in a tax return isn’t black and white—think of deciding what’s tax deductible and what’s not—I sensed balancing soil contamination and growing edibles had shades of grey, too.
So I set out to see how urban veggie growers can best tackle the question of soil contamination without being mired in conflicting numbers.
What Other Growers Do
Travis Kennedy, an agrologist involved in community garden projects, also raises produce at his Lactuca Micro Farm in Edmonton. “Pragmaculture,” he responds with a laugh, when I ask how he deals with possible soil contamination. His pragmatic approach to urban agriculture is to always use raised beds, bringing in soil he knows is safe, because he always assumes that there may be contamination.
Ward Teulon, also an agrologist, runs City Farm Boy in Vancouver, designing and building vegetable gardens. Teulon explains that sending backyard soil samples to a laboratory doesn’t always give a clear picture of what’s in the soil because urban soils are moved around a lot and are not uniform. He agrees, however, that interpreting results from expensive tests, which can cost hundreds of dollars, can be daunting. If there is a cause for concern, he believes money is better spent bringing in soil to make a raised bed. “Find out your property’s history,” he advises, because many urban soils are perfectly fine.
Luckily for me, my property’s history seems clear-cut, from agricultural to residential.
So, aside from the paint-chip-infested soil beside the house, I’m not worried. Gardeners who don’t know the history of their site could ask neighbours about past use and nearby properties, or check municipal records or archives.
Grow a Container Vegetable Garden
And get an early harvest of crops that usually take too long!
Asssessing the Risk
In 2014, Toronto Public Health created a plain-language guide to help gardeners understand the issues surrounding possible soil contamination and growing edibles.
Josephine Archbold, who helped write the Guide for Soil Testing in Urban Gardens, says it’s wrong to think only experts can figure out when to grow and when to worry.
The guide moves away from the notion that soil is either safe or unsafe—a black-and-white approach.
“I think we need to move beyond the concept of ‘safe’ and ‘not-safe’ cut-off levels that tell gardeners to either garden (100 per cent) or not garden at all (0 per cent),” she says. Instead, the guide is intended to help gardeners think about the risk of contamination for a site, and gives options to deal with the situation. Testing is expensive, and raised beds can be expensive, too, so the guide encourages taking such actions only when the risk of contamination makes them appropriate.
Three-Step Guide
Step 1
Former orchard land is among those sites considered medium concern because of the legacy of old metal-containing sprays.
In the three-step guide, the first step is to establish a level of concern by looking at former land use. With high-concern sites (e.g., former gas stations), contamination is very likely, so the guide recommends skipping expensive tests and using risk-minimizing measures such as raised beds, container gardening, or cultivating fruit and nut trees—for which contaminant uptake isn’t a concern. Nor is soil testing recommended for low-risk sites (e.g., long-term residential areas).
There are medium-concern situations (e.g., hydro corridors and former commercial land) where testing is recommended, but even then, if gardens are smaller than 170 square feet (16 sq. m), raised beds are suggested because the cost of raised beds for such a surface area is likely less than testing. Surprisingly, former orchard land is among those sites considered medium concern because of the legacy of old metal-containing sprays.
After investigating the history of the garden site, another part of establishing a level of concern is physically inspecting soil: dig in a few random spots to see if there are unusual stains or odours, and note old equipment, tanks and debris that might provide clues to dumping. Dumping, burning, smells and staining can make for a high-concern site.
Step 2
When it comes to step two, testing the soil, the guide lists common contaminants, including some metals (such as lead, arsenic and cadmium), along with PAHs (polycyclic aromatic hydrocarbons), which Archbold explains are compounds that indicate past industrial activity. “Our soil screening values are specifically for urban gardening,” she says.
Create Your Own Unique Edible Landscape
That fits for your yard, and your style!
Step 3
The third step is to take actions to reduce risk. In keeping with the guide’s approach, the screening values don’t tell gardeners to either garden or not garden. The values help guide the actions of gardeners. For example, if test results or site history present a medium concern, suggested tactics are lowering the level of contaminants by adding clean soil and organic matter. Archbold says adding organic matter makes many contaminants less mobile.
Another example of how to reduce risk is reducing soil dust by covering soil with a mulch, peeling root vegetables before eating and avoiding crops more likely to accumulate contaminants (cabbage family, beets and spinach).
Suspect Contamination?
If you suspect contamination and opt for testing instead of raised beds, containers, or fruit and nut trees, the guide gives pointers about how to find an accredited lab in your area. When collecting soil samples, there are some important steps to follow—and the guide gives instructions for this as well.
As for the strip beside my house, I will plant a fruit tree. I still don’t know how many parts per million lead are in the soil there, but because the site inspection (namely, digging and seeing all those paint chips) points to a possibility of contamination, my guess is that lead levels could be on the high side. It’s a very small space, so I’ve ruled out expensive testing.
I’ve also ruled out a raised bed because I don’t want to redirect water into my neighbour’s yard. So, a fruit tree seems to me to be the most practical approach—and is an acceptable shade of grey for me.
Originally published in Garden Making Magazine, Spring 2014
