Rhubarb is a cool season, perennial plant that is very winter hardy and resistant to drought. Its crop is produced from crowns consisting of fleshy rhizomes and buds. Following a season of growth the rhubarb crown becomes dormant and temperatures below 40 °F / 5 °C are required to stimulate bud break and subsequent growth. The first shoots to appear in the spring are edible petioles and leaves. These emerge sequentially as long as temperatures remain cool (below 90 °F / 32 °C). As temperatures increase, top growth is suppressed, even appearing dormant in periods of extreme heat. With declining temperatures in later summer, foliage growth resumes.
Rhubarb tolerates most soils but grows best on fertile, well-drained soils that are high in organic matter. A clean planting site is essential for the cultivation of rhubarb since no herbicides are registered for use on rhubarb. Small areas of perennial weeds can quickly build up to serious proportions. To prevent this, all perennial weeds should be killed the year before planting. The fields should be cultivated in the spring and after cutting, and hand hoeing may also be necessary. Rhubarb is relatively free of insect and disease problems.
Rhubarb is rather tolerant of soil acidity but does best in slightly to moderately acid soil. The crop can tolerate soil pH as low as 5.0; however, maximum yields are attained at a pH of 6.0 to 6.8. Liberal quantities of fertilizer are needed. Rhubarb responds well to fertilizers. The quality of the crop harvested depends to a large extent on the care and fertilization received. Home gardeners should give each plant 1 cup (about 2 handful's) of 10-10-10 fertilizer each spring, applied in a circle around the plant when growth starts. Fertilize each year and cultivate shallowly as often as necessary to remove weeds.
Manure is an extremely valuable source of organic matter as it helps to conserve moisture, preserves the soil structure, and makes nutrients readily available. Manure should be applied before planting one to two shovels per plant for home gardeners. An application of composted manure or leaves is beneficial in late fall and early winter, but do not cover the crowns as this may promote rotting. Fresh manure should not be used as this will burn the tender rhubarb plants.
Rhubarb responds to good care and watering. Remove the flower stalks as they are seen. During the first year of planting, the stalks should not be picked, since food from the leaves is needed to nourish the roots for the next year's growth. One light picking may be taken during the year following planting if the plants are vigorous, and beginning the second year following planting, the entire plant may be harvested. When harvesting rhubarb, the first step is to cut the stalks at the soil line or simply pull them out individually. All of the stalks of a plant may be harvested at one time, or pulled out selectively over a 4-6 week period. After the stalks are cut, the leaves may be removed. For the home gardener, rhubarb will tolerate a fair amount of neglect and still thrive, they are very tough plants.
The rhubarb season runs from April to September. Refrain from harvesting rhubarb the first year after planting. Each plant needs time to build up food reserves in the root to produce thick, robust stems.
Established rhubarb plants can be coaxed into early outdoor production by covering plants with clear plastic in the early spring, before the crown starts to grow. As growth starts, cut 1/4 inch ventilation holes in the plastic. As leaves get larger, cut the plastic to keep the leaves free.
Rhubarb hit by a frost or freeze can still be eaten provided the stalks are still firm and upright. Leaf injury may be noticeable with some brown or black discoloration on the edges. If the stems appear soft and mushy, do not eat them. Severe cold injury may cause the oxalic acid crystals in the leaves to migrate to the stalks increasing the likelihood of poisoning problems. If in doubt about the safety of eating the stalks, don't. Cut those stalks off and compost them. Allow new stalks to develop before eating, or if it is the end of the growing season, try forcing some rhubarb indoors
Rhubarb needs cold to trigger spring growth. Rhubarb tolerates very cold (-20 F) very well. Collect the last few stalks after the first hard frost and throw them on the compost pile. Then spread a layer (2-3") or compost (or leaves or hay) to prevent winter winds from drying out your roots. You don't need to do much. Established clumps will have to be trimmed every 4 to 5 years or when the stalks get small and spindly or when the crown is visibly crowded. This will help the plant to keep growing nice thick stems. This is done by digging around and trimming the crown down to 4 or 5 buds. You can also use this opportunity to divide your plant into more plants. You may encounter is rot in the crowns from excessive water in the crown area. If so, destroy these plants.
Generally, harvesting begins in late May or early June, with an option of a second harvest made in late August. The stalks should be firm at harvest. If they are harvested too late they become pithy and tough. Harvesting should be delayed until the second year following planting to permit accumulation of root reserve. During the second year, a light harvest may be taken and normal harvests may begin in the third year. Stalks may be clean cut, taking the entire plant at the soil line or harvesting sequentially by pulling the stalks at the prime size over a period of 4-6 weeks. Do not remove more than 2/3 of the fully developed petiole from any plant at harvest. As stalks are cut, leaves are removed and left in the field or they can be composed.
Select petioles that are bright pink, crisp and free of disease or insect damage. Young, dark pink, smaller diameter petioles are sweeter and more tender than thick, long green ones, but this also depends and the particular variety of Rhubarb. Don't cut the Rhubarb stalks from the plant, but instead snap them off. They will come away quite easily and this is much better for the plant. I grab a stalk right down where it emerges from the ground, and use a sort of rocking, twisting motion. Visualize snapping away a single celery stalk from the bunch. If the stalk is grasped too high it snaps in two. At any given time, harvest less than 1/3 of the stalks from any one plant. Rhubarb may be harvested later but very few stalks should be taken from any one plant. Rhubarb, if not used immediately, can be stored by refrigeration, caning, freezing or drying. Cut all of the leaf away from the Rhubarb petiole and the petioles will keep well in the refrigerator for two to three weeks in sealed plastic bags.
Oxalates are contained in all parts of rhubarb plants, especially in the green leaves. There is some evidence that anthraquinone glycosides are also present and may be partly responsible. It is not clear as to the exact source of poisoning from rhubarb, possibly a result of both compounds. The stalks contain low levels of oxalates, so this does not cause problems. The basic tip is do not eat the leaves, only the stalks are edible.
Here is a photo of the rhubarb plant a friend shared with me from her garden. I planted it yesterday and I hope to get a harvest this year.
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| A view of the crown from above |
Two weeks after transplanting it looks like this:
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