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

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.

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.”