If you are planning on growing rhubarb in your garden this year, you might be wondering how big they will get. That way, you can plan the number of plants and the amount of space you will need for your crop of rhubarb.
So, how big do rhubarb plants get? The stalks on a rhubarb plant are 2 to 3 feet (61 to 91 centimeters) tall. The plant itself is 2 to 3 feet (61 to 91 centimeters) wide, since the plant’s stalks and leaves can spread in all directions from the roots.
Of course, the quality of your rhubarb (if you get any at all!) depends on the care that you give your plants. Let’s take a closer look at rhubarb, including size, growing conditions, and time to maturity.
How Big Do Rhubarb Plants Get?
The stalks (that is, the edible part) of a rhubarb plant can grow 2 to 3 feet (61 to 91 centimeters) tall on a mature plant. A mature rhubarb plant can have a spread of 2 to 3 feet (61 to 91 centimeters) in all directions.
The leaves (the part of the plant that is toxic to humans) are very large – some of the largest that you will see in your garden. I have seen rhubarb leaves up to 1 foot long and wide, but I’m sure they can get larger than that!
How Long does it Take Rhubarb to Grow?
Rhubarb takes a long time to grow, so you must be patient to enjoy the stalks of this plant. It will take at least 1 year before you can harvest any stalks from a rhubarb plant – even longer if you grow them from seed!
If you buy rhubarb crowns and transplant them into your garden, you should not harvest any stalks in the first year of growth. In the second year, you can harvest a few. (Add a year to these time frames if growing rhubarb from seed.)
Rhubarb seeds will generally germinate in 2 to 3 weeks, given proper soil moisture and an ideal temperature of 70 to 80 degrees Fahrenheit (21 to 27 degrees Celsius).
How do You Know When to Harvest Rhubarb?
As mentioned above, you should not harvest rhubarb in the first year after planting, since the plant will need all of its energy to continue growth.
Usually, you harvest rhubarb from May to July in the 2nd year (if growing from crowns) or the 3rd year (if growing from seed).
For more information, check out this article on rhubarb from Johnny’s Selected Seeds.
When you harvest rhubarb, use a knife cleaned with alcohol to cut the stalks. Wipe the blade with alcohol between cuttings, to avoid spreading disease between plants. Cut off the leaves from the top of the stalks, since they contain oxalic acid, which is toxic to humans.
Also, remember not to harvest rhubarb after a frost or freeze. The leaves contain oxalic acid, which is toxic to humans. This toxin can move from leaves into stalks after a frost or freeze.
For more information, check out this article on rhubarb from the University of Minnesota Extension.
Finally, be sure to leave 6 stalks on the plant, so that it can absorb sunlight and continue to store energy for future growth.
Why Is My Rhubarb So Small (or Thin)?
Newly planted rhubarb will have small, thin stalks in the first year or two before the plant becomes well-established. Lack of water, nutrients, or sunlight can also cause small stalks.
For more information, check out this article on small rhubarb stalks from the Iowa State University Extension.
Also, keep in mind that older rhubarb plants may end up with smaller stalks if they become larger than the soil can support.
In that case, you can divide the rhubarb plant and transplant the parts to different areas in your garden. If you do divide your rhubarb, do it in early spring, before the plants begin to grow.
For more information, check out this article on dividing rhubarb from the Michigan State University Extension.
What do Rhubarb Plants Look Like?
Rhubarb grows close to the ground, with many stalks growing out from the root ball and crown. Rhubarb stalks are tall, with red or green coloring.
Each rhubarb stalk has one large leaf at the top. A rhubarb stalk and leaf looks similar to Swiss chard, but much taller and larger, with much rougher leaves.
Is Rhubarb Hard to Grow?
Rhubarb likes full sun, so be sure to plant them in an area where they get 8 or more hours of sunlight per day. Avoid planting rhubarb in a place where they will be completely shaded by a tree or tall neighboring plants (such as tomatoes).
Rhubarb is a perennial, and they can live for 10 to 15 years or longer with proper care. Remember to plant rhubarb somewhere it can stay for many years without being disturbed.
Rhubarb grows best in well-drained, loamy soil with a pH of 6.0 to 6.8 (slightly acidic). However, there are many other factors that affect rhubarb growth, including temperature, watering, fertilizing, and spacing. Let’s start with temperature.
Temperature for Rhubarb
Rhubarb seeds are often sown directly into the soil outdoors, 2 to 4 weeks before the last frost. You can find frost dates for your area on the Old Farmer’s Almanac website.
However, this may not be an option in a climate with a short growing season. In that case, you should start your rhubarb seeds indoors 8 weeks before transplanting them into the garden.
Another option is to buy rhubarb crowns. You can plant rhubarb crowns in early spring (as soon as the ground is workable, or no longer hard with frost). You can also plant in the fall after the crowns are dormant (4 to 6 weeks before the first fall frost).
For more information, check out this article on rhubarb from the Old Farmer’s Almanac.
The ideal (optimal) temperature for rhubarb seed germination is between 70 degrees Fahrenheit (21 degrees Celsius) and 80 degrees Fahrenheit (27 degrees Celsius).
Keep in mind that these temperatures refer to soil temperature, not air temperature. If you want to find out the soil temperature, use a probe-type thermometer to check.
If the thermometer reads a temperature that is too low, then you have some options. One option is to wait until the sun warms up the soil.
To speed up this process, clear away any debris, such as leaves or grass clippings, from the soil surface. Also make sure to choose a location for planting that gets plenty of sun, so that it can warm up the soil faster.
If you are worried about a short growing season, you can also use a cloche (a plastic or glass cover) to trap some heat and warm up the air and soil near your rhubarb seeds.
A cloche can be made from a plastic water bottle to retain warmth and humidity in the soil for seeds or seedlings as they grow.
According to the Oregon State University Extension, “rhubarb can withstand down to 35 F without damage. Rhubarb needs at least 500 hours of winter temperatures between 28°F and 40°F to properly form new leaf buds.”
Watering for Rhubarb
Water rhubarb deeply and less frequently – provide enough water to get the entire root ball wet.
Putting mulch on top of your soil will help to retain moisture, especially during periods of hot, dry weather. If you find that you have a problem with dry soil, check out my article on how to treat dry soil.
On the other hand, over watering your rhubarb plants (or any plants for that matter) can lead to root rot and eventual death. The best way to decide when to water is to feel the soil with your fingers.
If the soil feels dry 2 or 3 inches below the surface, then go ahead and water. For more information, check out my article on over watering your plants.
Try to water early in the morning, rather than at night, to allow water to soak into the soil before evaporating.
Fertilizing for Rhubarb
Once the ground freezes, cover rhubarb with 2-4 inches of compost. For more information, check out my article on making compost.
To fertilize your rhubarb plants, use ½ cup of 10-10-10 fertilizer around each plant in early spring, before growth starts. After 4-5 years, you can switch to nitrogen-only fertilizer for most soils.
For more information on fertilization, check out this article on rhubarb from the Iowa State University Extension.
Spacing for Rhubarb
When you plant rhubarb crowns, bury the roots so that the crown bud is 2 inches below surface of soil. Leave 3 to 4 feet between plants, with rows 3 to 4 feet apart.
For more information on spacing, check out this article on rhubarb from the University of Illinois Extension.
By now, you have a much better idea of how big rhubarb get. You also know a bit more about the care that is necessary to ensure a healthy crop of rhubarb in this year’s garden.
I hope you found this article helpful – if so, please share it with someone else who can use the information. If you have any questions or advice about rhubarb, please leave a comment below.