Growing Rhubarb is considered a vegetable in most of the world. However, in 1947, a New York judge ruled that rhubarb is a fruit, thereby lowering taxes.
Growing Rhubarb in the U.S. began in the 1820’s when it was first imported to Maine and Massachusetts. Early settlers took plants with them as Americans migrated West.
In the Middle Ages, rhubarb was grown in China and was more expensive than spices like cinnamon because it had to be (they thought) imported from China – which at that time was a good thing!
Laura Ingalls Wilder, in her book “The First Four Years,” refers to growing rhubarb as growing “pie plant.” Rhubarb pie is still a favorite of many people, including myself!
WHEN TO PLANT RHUBARB
If you’re starting rhubarb from seed, plant the seeds about 6 weeks before the last frost. Do note, though, if you plant from seeds rather than root stock, you’ll wait at least 2 years (1 additional year) to harvest your rhubarb roots.
If you’re planting from root stock or crowns, plant or divide the roots/crowns in early spring while the plants are still dormant. This is the favored method for planting rhubarb, particularly in the Northern climates.
Rhubarb, once planted in Northern climates like where we live, will thrive in the cooler spring temperatures. It begins growing once soil temps reach a little over 40°F.
You can also plant roots/crowns before the ground freezes in the fall, provided you mulch over top of your plants with 8 to 12 inches of mulch.
Rhubarb generally does not do well in Southern U.S. climate zones due to not liking temperatures over 90°F. However, it can be grown during the cool season in some sub-tropical and tropical areas.
BEST PLANTING AREAS FOR RHUBARB
In the Northern areas, where rhubarb thrives best, rhubarb requires at least 8 hours of sunlight daily to flourish. In Southern climates, some afternoon shade is preferable, but does create more spindly stalks.
As with most plants, rhubarb doesn’t really like soggy soil. Make sure the area you plant it in has well-draining soil with lots of organic matter in it.
PREPARING THE SOIL
The ideal pH level for growing rhubarb is about 5.5 to 6.5.
Rhubarb needs a good amount of nutrients to grow well. The best organic methods will include mixing lots of compost or composted manure into an area at least 12 inches deep and 3 feet in diameter. Mix in about 6 inches of compost/composted manure.
CHOOSING THE RIGHT VARIETIES FOR YOUR AREA
Many rhubarb plants, if grown in good soil with adequate sunlight, have a mature diameter of 5 to 6 feet. Happily, one plant is usually enough for most families.
Some of the new varieties of rhubarb have red to crimson stalks that are sweeter than some of the older varieties. Check with your favorite seed supplier for their advice on which varieties will fit your tastes best.
Check with your county extension office to see if there are any common diseases that afflict rhubarb in your area. If there are, they will be able to recommend resistant varieties.
One reason rhubarb does better in cooler climates is that it needs the ground temperature to drop below 40°F for at least a week to break dormancy and stimulate the rhubarb leaves to grow.
GETTING STARTED INDOORS
If you’re planting rhubarb seeds, soak the seeds for a few hours in water or a compost tea before planting in a good quality, sterile potting soil; the seedlings will take 2 to 3 weeks to come up.
Don’t use ordinary garden soil as it may have fungus, weeds, bacteria, or other things that can hamper your plants.
Plant the seeds about a ¼ to ½ inch below the surface of the soil. Plant 2 to 3 seeds per section or pot. Once 4 true leaves have formed, cut off the weaker plants.
TRANSPLANTING RHUBARB OUTDOORS
Most rhubarb is sold as dormant roots or crowns. Purchasing them this way from your local garden center or favorite mail order seed company will take a full year off getting to your first harvest.
If you planted seeds, though, you’ll need to “harden off” your plants off for at least a week before planting out in the garden. You’ll do this when the plants are 4 to 6 weeks old and are about 3 to 4 inches tall.
This simply entails moving your plants outdoors during the day and back inside at night for increasing lengths of time throughout the week.
Ideal temperatures at this point should be about 50° to 55°F at night and 70° to 75°F during the daytime.
If you’re planting crowns or roots, place them 1 to 2 inches below the surface of the soil. If you’ve purchased potted plants, plant them at about the surface level of the soil.
Give the plants at least 36 to 48 inches between the plants and at least 72 inches between your rows if you are planting a lot of rhubarb.
PLANTING SEEDS IN YOUR GARDEN
Except for Southern climate zones, planting seeds directly in your garden is not recommended, but if you live in the South, you can plant rhubarb in rows 72 inches apart.
Plant the seeds every 3 to 4 inches, then once the plants have reached 3 to 4 inches in height, thin them out to at least 36 inches apart as they’ll grow quite large in the next couple years.
If you’re planting crowns or roots, plant them 36 to 48 inches apart. Cover the roots 1 to 2 inches deep, but don’t cover the crowns.
BEST PRACTICES FOR GETTING A GOOD RHUBARB CROP
Here are a few tips to getting the best rhubarb crop from your garden.
During the first year, remove any flower stalks when they grow from your plant. This will give your plant more energy to put into the roots which will grow a stronger plant in subsequent years.
You’ll see flower stalks growing out from your plant as the weather warms into the summertime. Your plants may resume growth in the fall when the weather cools.
When the frost begins in the fall, the heavier frosts will usually kill the rhubarb plant that’s above ground. This is the time to fertilize for next year’s crop.
DIVIDING RHUBARB FOR BETTER YIELDS
As rhubarb gets older – around 8 to 10 years – the plants often become root-bound. There becomes such a mass of roots that the rhubarb plant yield often decreases.
This is the time to divide the rhubarb plants to help them regain their vigor. This is pretty much like replanting new root stock, so follow the procedures outlined above.
When you divide these plants, you can typically cut the old crown into 4 to 8 pieces. Just make sure each section has one strong bud.
Cut the roots into four to eight pieces. Each piece must have at least one strong bud.
Some gardeners will do this procedure after 5 years to keep their plants “fresh.”
This past gardening season we tested a liquid organic leaf spray fertilizer called Organic Garden Miracle™. We sprayed most of our garden plants with OGM™. The sprayed veggies were more robust than the unsprayed plants, and the flavor was superior as well – sweeter and juicier. You may want to give OGM™ a try on your rhubarb. We’re pretty impressed.
MULCHING & WEEDING
It’s always a good idea to mulch growing rhubarb with straw or grass clippings or chopped leaves to keep the weeds down and the soil moist.
In the fall, after the plant has been killed by the frost, it’s also a good idea to cover the crown with 6 to 12 inches of clean straw (no weed seeds) if you live in an area that gets prolonged cold spells.
Although we’ve never lost any of our rhubarb plants from cold spells (and we get some good ones in our area), it’s still good insurance.
Black plastic mulch isn’t considered a good idea for rhubarb as it likes cooler soil temps.
Once your rhubarb plant gets past the first year, it usually doesn’t get much competition from weeds, and especially if you mulch around your plants. In the first year or two, just hand pull any competing weeds.
RHUBARB WATERING REQUIREMENTS
As rhubarb is susceptible to crown rot, drip irrigation is your best option, about 12 to 18 inches from the crown.
If you don’t have any drip systems available, water early in the day so the plants can dry out by afternoon.
If you’ve added mulch around your growing rhubarb plants, watering an inch of water every 7 to 10 days should be sufficient to keep them producing juicy stalks.
Overwatering rhubarb can be quite harmful. We’ll discuss fungal diseases below.
COMPANION PLANTING AND ROTATION CONSIDERATIONS
Rhubarb grows well with brassica family members which include broccoli, kale, cabbage, and cauliflower.
While I haven’t personally witnessed this, some have said that rhubarb protects legumes (beans, peas, etc.) against the black fly.
Other sources state that rhubarb helps deter spider mites from columbine flowers…again, I haven’t tried this as we don’t have any columbines on our property.
Several gardening authorities claim that making a tea from boiled fresh rhubarb leaves will kill aphids and that the oxalic acid in the leaves will also prevent blackspot on roses.
Make sure if you have rhubarb that there are no dockweed plants in the area as it attracts a bug called the Rhubarb Curculio, a yellowish beetle that bores into rhubarb.
When you divide your rhubarb, make sure to plant the new roots into new areas so as to give the previous soil a rest.
WHEN TO HARVEST RHUBARB
Make sure you don’t harvest rhubarb stalks from your plant in the first year you plant it, and the first 2 years if you planted from seed.
In the late spring you can begin to selectively harvest rhubarb stalks. Depending on the variety, your stalks will be from 12 to 24 inches in length (up to the leaf).
If the stalks get too large, they can get stringy and tough. You’ll have to get a feel for the variety you’ve planted.
Redder varieties are usually sweeter and more flavorful than green varieties which are generally just plain sour.
Don’t harvest more than a third of the stalks or the plant won’t grow well. Wait until the leaves on a stalk smooth out; this is an indicator that a stalk is mature.
When you harvest the stalks, don’t cut them off with a knife as this may promote crown rot. Rather, use a slow, firm, twisting motion to pop the stalks away from their roots.
Once you’ve plucked a stalk, trim the leaves of immediately to prevent the stalk from wilting as quickly.
One myth we’ll dispel; rhubarb does NOT become toxic in the late summer. That’s an old wives tale.
If a seed stalk pops up from your plant, pull it out so it doesn’t affect your plant’s productivity.
Fresh rhubarb can be stored, wrapped in plastic, for up to 3 weeks.
You can also slice your stalks up and freeze them fresh for usage at a later date.
While we’ve never done it, I am told that rhubarb preserves are delicious. Can’t back that one up.
I can tell you, though, that rhubarb pie is a perennial favorite in the springtime with our family.
PREVENTATIVE AND NATURAL SOLUTIONS TO COMMON PESTS
The rhubarb curculio is the only real pest that afflicts rhubarb plants.
It is a yellowish to grayish-brown snouted beetle that ranges in size from ½ to ¾ inch long and bores its way into the stalks and crowns.
The best prevention is to keep dock weeds out of your garden as it is a host for these beetles. Also, keep grassy weeds under control around your rhubarb plants as well.
If you have a bad infestation, your best defense is to pull up your plants after the beetles have laid their eggs and burn or destroy the plants and start over. I’ve not seen any infestation of that magnitude.
Various root fungi can invade your rhubarb if it’s planted in poorly draining soil. Most root fungi can be avoided by simply either creating well-drained soil with organic matter and sand or planting it in an area that already drains well.
Planting in raised beds can sometimes help alleviate the poor drainage issue.
There are viruses that can attack your rhubarb plants, causing them to grow poorly. The only treatment we know of is to start over with resistant varieties. Check with your local county extension before you plant to see if there are viruses that affect rhubarb in your area. They can also recommend resistant varieties.
Various Leaf Spot diseases are common to rhubarb.
One of the most common leaf spot diseases is called Ascochyta leaf spot, and starts as a light green or yellowish spot on your rhubarb plant leaves which morph into white spots with red borders. The centers will often fall out, leaving holes in the leaves.
Ramularia leaf spots are another common disease. It starts as small red spots that develop a white or tan center and a purplish border.
Overwatering is key to promoting leaf spots, as is overhead watering late in the day. Water early in the day so the leaves dry out completely by afternoon.
Overcrowding plants can also encourage leaf spots, as can grassy weeds.
Remove these leaves in the fall and burn or dispose of them after the frost kills the plants. This will help your plants the following year.