Rhubarb, nicknamed pieplant, is a wonderfully old-fashioned veggie-garden regular that produces a reliable summer crop year after year. Once established, rhubarb plants will produce an edible harvest for at least 8 years, even up to 20.
But when should you plant rhubarb? Generally, you can plant rhubarb in spring or late in the fall. If you are growing rhubarb from seed, plant eight weeks after the last frost date. Plant rhubarb crowns when the ground is workable. In the fall plant once the rhubarb is dormant.
Planting Rhubarb in Different Climates
Rhubarb is a hardy plant that can withstand temperatures as low as 35°F (1.6°C). It thrives in most parts of North America.
Rhubarb crowns and the woody rhizomes don’t suffer any ill effects when left in very cold, dry soil for months, even if they are frozen.
In fact, rhubarb grows best in planting zones where the ground freezes in winter. But frost will cause the leaves and shoots to die back.
It needs at least 500 hours (about 3 weeks) of winter temperatures between 28 and 40°F (-2 and 4.4°C) to form new leaf buds.
It also needs temperatures of above 40°F (4.4°C) in spring to break dormancy and start growing. Because it’s a cool-season vegetable, it does best when the average winter temperature is below 40°F (4.4°C).
It needs summer temperatures that average less than 75°F (24°C) during the growing season.
According to the Oregon State University (OSU) Extension Service, spring low temperatures and cultivar genetics help the development of pink-to-red pigment in rhubarb stalks. Parts of Oregon are high-desert and very dry, so they recommend growing the plant where it gets late afternoon shade in summer.
This illustrates how different climates can affect specific practices that relate to growing rhubarb in your home garden.
According to the University of Minnesota Extension, rhubarb grows best in zone 4 where the annual extreme minimum temperature is -20 to -30°F (-28.9 to -34.3°C).
Nevertheless, rhubarb is grown successfully in USDA plant hardiness zones 3-8. The minimum temperature in these zones varies from -40°F (-40°C) to 10°F (-12.2°C).
Köppen climate classifications can be useful too. Although broad, these are as relevant as the plant hardiness zones.
Just remember that hardiness to cold weather isn’t the only factor that makes an impact on planting and growing vegetables. You need to find out about elements like humidity, rainfall (which the Kӧppen system does), and the average length of a typical growing season.
Also, if you grow rhubarb in warm climates, they probably won’t continue to reproduce year in and year out.
Köppen Climate Classifications
There are five main climate types originally defined by the German botanist-climatologist Wladimier Köppen. All except one (a dry climate) is defined by temperature, like the plant hardiness zones.
This is the warmest climate type and the temperature of the coolest month is at least 64.4°F (18°C). This equates with zone 13, which is much too hot for growing rhubarb.
There are also three subtypes defined by rainfall, although this won’t be a factor for rhubarb:
- No dry season
- Short dry season
- Winter dry season
A dry climate may be arid or semiarid, as well as warm or cold.
Rhubarb is relatively drought tolerant. If your climate is semiarid and warm, you can probably grow rhubarb successfully, especially if you irrigate regularly.
Like tropical climates, temperate climate types factor in dryness:
- No dry season
- Winter dry
- Summer dry
The temperature in the coldest month is between 64.4 and 26.6°F (18 and -3°C). In the hottest month it is at least 50°F (10°C).
This is not the ideal climate for growing rhubarb, but it does get cold enough in zone 9 areas.
Continental climates have the same dry differences as temperate climates, but with a fourth subtype. This indicates the warmth of summer or the coldness of winter.
Temperatures in continental climates vary a lot, and some colder areas are ideal for growing rhubarb.
This is the coldest type of climate and it is divided into tundra and snow/ice climates. The temperature is always below 50°F (10°C).
You can grow rhubarb in insulated growing tunnels, but not out in the open.
Choosing Rhubarb Seeds
Rhubarb can be propagated by dividing plants, from bare roots, or from seed. You can also buy established plants in pots from garden centers.
If you are planning to grow rhubarb from seeds, you’re going to need a lot of space.
Rhubarb is large and plants will grow to 2-3 feet (62-92 cm) tall. You will need to ensure plants are about 4 feet (122 cm) apart to avoid overcrowding.
There are some superb heirloom seeds available, but check quantities before you buy. Some packets have a manageable handful of seeds (5-8) while others have as many as 500!
You will also need patience. Even though your seeds may sprout in 5-10 days, you will need to wait until the third season before harvesting.
The recommended way to grow rhubarb is by subdivision of rhubarb crowns. You can buy crowns or divide the crowns of established plants that are between 5 or 6 years old.
When planting bare-root or rhubarb crowns you should wait until the second season before harvesting.
Different Rhubarb Varieties
Whether you are planting seeds, bare roots, or crowns, there are lots of choices.
According to the University of Maine Cooperative Extension, there are about 67 rhubarb species and many cultivated varieties. These include:
- Crimson Cherry
- Crimson Wine
- Crimson Red
- Canada Red
- Cherry Red
They warn that while many people choose rhubarb based on the color of leaf stalks, the color is not consistent year after year. There are also varieties with green stalks
Whichever variety you choose to grow, be aware that only the rhubarb stalks are edible. Rhubarb leaves are toxic because they contain high amounts of oxalic acid that can make you sick.
How to Plant Rhubarb Seeds
Your first step will be to choose a suitable site for your rhubarb to grow in.
It usually grows best in full sun in soil that drains well and is high in organic matter. But, if you live in a warm climate, make sure your plants get afternoon shade.
Light soils tend to produce a crop earlier but may not hold moisture. This means watering will be critical during the growing season.
The pH of the soil isn’t critical, but it prefers slightly acidic soil. If you have a pH test kit, aim for 6.0-7.0.
If your soil is clay, a raised bed is the answer.
Planting Rhubarb Seeds & Crowns
You can start the seeds indoors about 6 weeks before the last frost date. Otherwise, transplant or direct sow about 8 weeks after the last frost date.
The best soil temperature is 60-75°F (16-25°C).
If planting indoors, cover the seeds lightly with soil and give them heat from underneath to improve germination.
When planting directly into a garden bed, till or fork the soil to a depth of at least 61 cm/24 inches below the soil surface. This will let your plant grow and give the roots plenty of space to develop.
When planting bare-root plants or rhubarb crowns, make sure that the crown is level with the soil surface.
How to Water Rhubarb
Always water well after planting. Rhubarb thrives in moist soil, and so regular watering is also essential during the rhubarb growing season.
It is good practice to water every 7-10 days, especially in mid-summer when temperatures are high. Make sure the soil gets a good soak to at least one or so inches below the soil surface.
How to Grow Rhubarb
Rhubarb is a hardy perennial that will grow back each year in the same location. And if you’ve chosen the right spot for it, it’ll get bigger and bigger.
Even though it’s a low-maintenance plant, you’re going to need to subdivide it every 4-6 years after planting, in early spring. If you’ve got enough rhubarb plants to feed your family and friends, gift them with subdivided crowns.
How to Subdivide Rhubarb
Divide your large plants early in the spring before they get their first growth spurt.
Dig the whole clump of roots out of the ground and cut down between the buds on the rhubarb crown. Each new section should have at least 2-3 buds.
Replant the divided rhubarb crowns as soon as possible. Space them 3 feet (about 92 cm) apart.
The rhubarb harvest season lasts for about 8 weeks and the best time to harvest is from May to mid-July. The plant will become dormant in August and September.
But, there are a few golden rules to remember:
- Never harvest during the first year of growth
- Only harvest when the stalks are 12-18 inches long and at least ¾ inch (20 mm) in diameter
- Remove the flower stalks to prevent them from draining the strength of the plant
When you harvest rhubarb, pull the stalks and twist them. Discard all the toxic leaves.
After this, pull a few of the thicker sticks when long enough. Stop harvesting in early summer and allow plants to grow freely for the rest of the season.
Pests & Diseases
Rhubarb isn’t usually affected by pests or diseases, although it’s a good idea to watch out for aphids, slugs, and snails.
Rhubarb curculio, a very large snout-nosed beetle, can be a problem. It doesn’t feed on rhubarb like other pests, but bores into the stalks, roots, and crown to lay its eggs.
If you see black spots on your leaf or flower stalks, it could be this beetle, which is a species of weevil. Pick it off by hand.
Crown rot and leaf spot diseases can also be a problem.
How Long Does Rhubarb Take to Grow?
It generally takes 5-10 days for rhubarb seeds to germinate and 2-3 weeks for the seedlings to emerge out of the ground.
Even though they will grow to maturity quite quickly, you will have to wait until two years after planting before your first harvest. If you’ve grown your plants from seed, you will need to wait three years before harvesting rhubarb stalks.
Rhubarb is an easy plant to grow and it keeps on giving an edible bounty for years. It has minimal pest and disease problems and requires very little ongoing care.
It’s an old-fashioned tart-tasting plant though, and not to everyone’s taste.
Nevertheless, why not give it a try? It might even become a new family favorite!