Rhubarb is a hardy perennial vegetable that produces one of the first harvests of the growing season. The edible portion of the rhubarb plant is the petiole – or leaf stem (sometimes also called the stalk). The rhubarb harvest is used to make pies, jams, and desserts, often in combination with strawberries and lots of sugar! But, harvesting the petioles at the wrong time or in the wrong way can impact future plant growth. This article discusses when to harvest rhubarb for the best flavor and yields.
What is rhubarb?
Perennial plants native to Asia, rhubarb (Rheum x hybridum) is a member of the buckwheat family. Rhubarb plants make a bold statement in the garden, with large leaves and brightly colored stems. When mature, a rhubarb plant grows to a height and width of 3 feet. Each leaf can be between 12 and 18 inches wide. They are very ornamental plants, so don’t hesitate to plant rhubarb in perennial beds and borders, as well as in the vegetable garden or even in raised beds.
Rhubarb grows from fleshy roots called rhizomes that can live for many years. These underground rhizomes are thick and fibrous. Leaves emerge from the crowns of the plants early in the spring. Some varieties, like ‘Victoria’, produce a green stalk with red speckles, while other varieties, like ‘Canada Red’, ‘Valentine’, and ‘Crimson’, have classic cherry red leaf stems.
The edible leaf stems of rhubarb are fairly sour tasting (hence the addition of sugar to most recipes). The harvestable stems are thick and juicy and can grow 12 to 18 inches long.
Where can you grow rhubarb?
This veggie is an excellent choice for all cold climates. Rhubarb plants need winter temperatures to drop to at least 28 to 40° F for a minimum of 500 hours in order for the plant to break dormancy in the spring. The plants are extremely hardy, surviving temperatures down to -30°F. As long as the roots are not sitting in very wet soil, they will survive even the harshest winter without harm. When spring temperatures hit about 45°F, the plants come out of dormancy and growth begins.
The best planting sites for growing rhubarb contain rich, well-draining soil, amended with compost and free of weeds. Full sun is best. Less than 8 hours of sun per day results in weak stems and floppy plants. The more sun, the better.
Why knowing when to harvest rhubarb is so important
It’s important to note that rhubarb leaves are toxic to humans and other animals. The leaves contain a high concentration of oxalic acid that can make you sick. In large quantities, oxalic acid can be fatal due to its ability to bind to calcium ions in your blood which leads to kidney problems and even death if enough is consumed over a long period of time. But don’t let that stop you from enjoying rhubarb stalks! In the spring and summer, the thick stalks do not contain any oxalic acid. Harvesting rhubarb stalks during this time period is perfectly safe, as long as you cut off the leaves.
Later in the season, however, you’ll want to refrain from harvesting rhubarb so the plants can “recharge” and store up ample energy for the following year’s growth. Stick to harvesting in the spring and early summer, and you’ll be good to go.
When to harvest rhubarb for maximum flavor and yields
In addition to concerns about oxalic acid content, it’s important to know when to harvest rhubarb for the best flavor and to maintain optimum plant health. Prime harvesting season for rhubarb is in the early spring, when the stems are tender and juicy, and before they become tough and fibrous. The best time is a harvest window of about 8 weeks, beginning in May and continuing through June. You can also harvest an occasional handful of stems through July, but after that, do not make further harvests.
Harvest in the morning when the plants are well hydrated and not stressed by the heat of the afternoon. This results in juicy stems that stay fresher longer.
When to harvest rhubarb also depends on the age of the plant. For newly planted rhubarb plants, do not harvest during their first year of growth. In their second year, harvest only up to 4 stalks per plant. In their third year and beyond, harvest as many stalks as you’d like, as long as the plant always has at least 6 stalks remaining to fuel continued plant growth. If you harvest too heavily, plant performance will be affected and subsequent stalks will not be as thick.
The best way to harvest rhubarb
While many gardeners harvest rhubarb by cutting the petioles with a sharp knife or pruning shears, it’s much easier and better to harvest with a twist. Harvesting with a knife leaves stubs of rhubarb stalks behind. These stubs rot, and that rot can spread to the plant crowns, especially during wet springs. Instead of cutting, when rhubarb harvest time arrives, grasp a leaf stem at the very bottom, give it a small twist, and pull it sideways to remove the stalk at its base. This technique leaves no stub behind to rot. The sideways tug prevents injury to the rhizome and future developing buds. Each bud produces several stalks, so damaging it can impact future harvests.
Each mature plant should yield several dozen stalks per season. After the stalks are harvested, cut the leaves off completely and toss them onto the compost pile like you would any other plant debris. The composting process breaks down the oxalic acid found in them. Finished compost that contains rhubarb leaves is fine to add back to the garden.
When to stop harvesting rhubarb
While your focus may be on when to harvest rhubarb, it’s also important to understand when to stop harvesting rhubarb. To ensure ample rhubarb harvests next year, be sure to stop picking leaf stalks by the end of July. The remaining leaves will provide energy to fuel continued plant growth. In my own garden, I stop harvesting in late June because I find the flavor is superior in the spring. Once early July arrives, I find the stalks get tough and don’t taste as good, but it’s okay to harvest them as late as the end of July.
What to do when a rhubarb plant makes a flower stalk
Some gardeners worry when they spy a flower stalk developing from the center of their rhubarb plant. It’s nothing to worry about, but you do want to remove any flower stalks as soon as possible. For rhubarb plants, flower production saps energy from the plant. This prevents the leaf stems from reaching their maximum potential. The trick to growing long and broad stems is to cut off any flower stalks the moment you notice them. Do not wait for the flower stalk to fully develop or for the buds to open. As soon as you see the flower stalk growing up out of the center of the plant, use a sharp pair of pruners to cut it off at its base. You can’t stop the flowering from happening, but you can “nip it in the bud”.
Why isn’t my rhubarb plant producing more leaves?
If your rhubarb plant isn’t performing up to snuff, here are a few things that could be going wrong.
- Limited production may be the result of self-competition. If rhubarb becomes crowded and over-grown, it can suffer. Dig up and divide the crowns every five to eight years in the early spring.
- The crown may be planted too deeply. Rhizomes should only be 1 to 2 inches beneath the soil. Dig up and replant if necessary.
- Too much shade can also result in few stems or floppy, weak stems. Move the plant to sunnier conditions.
- Remove flower stalks asap. As mentioned above, letting the plant go to flower can weaken it and result in a poor harvest the following season.
- Petiole production is also negatively impacted by over-harvesting. Remember, a big part of knowing when to harvest rhubarb is also knowing when to stop harvesting.
What to do with rhubarb plants at the end of the season
When late fall arrives, your thoughts should shift from when to harvest rhubarb to how to prepare the plant for winter. The foliage of your rhubarb plant will be blackened by the first hard frost, but don’t worry. There’s nothing special you need to do to see the plant through the winter. Remember, this is an extremely hardy species that does not need supplemental mulch or even fertilizer to survive the winter with flying colors. Once the ground freezes, the roots will sit dormant until warm spring temperatures arrive again.
How to store harvested rhubarb
Knowing when to harvest rhubarb quickly turns into knowing what to do with all that rhubarb! There are many recipes for using this tart vegetable. Its flavor is unique, and among my favorites is this rhubarb muffin recipe and this rhubarb ice cream sauce recipe.
Harvested rhubarb stalks can be stored in a plastic freezer bag in the refrigerator for up to two weeks. I wrap the bottom end of the petioles with a very slightly damp paper towel to keep them plump and juicy.
More about when to harvest rhubarb, plus growing tips
- Rhubarb does not face many problems from pests, though Japanese beetles can occasionally damage the leaves. Not to worry, though, as the leaves are not something you’ll be harvesting anyway.
- Slugs can be a common problem as well. Here are some great ways to manage slugs organically.
- Rhubarb is a pretty self-sufficient plant. Provide nutrients via a complete organic granular fertilizer. There’s no need to dig it into the soil; simply sprinkle it around the plant in the autumn. The nitrogen and other nutrients found in it will be released slowly over time.
- Ensure your planting site has ample drainage, especially in the winter. Rhubarb crowns will rot if left in standing water during the winter months. Too much moisture in the cold season can spell death for this perennial vegetable.
With the right care and understanding of when to harvest rhubarb and how best to care for the plants, gardeners can enjoy decades of harvests. The easy nature and beautiful appearance of this plant make it a star of the spring (and summer!) garden.
For more advice on harvesting various vegetable crops, please visit the following articles:
- The best time to harvest beets
- When to harvest spinach
- Timing the tomatillo harvest
- When to pick carrots for maximum flavor
- How to harvest herbs
- Proper timing for garlic harvests