How to care for your rhubarb in early spring

Carol Savonen
Special to the Statesman Journal
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Rhubarb grow in early spring. But don't eat the leaves. They are poisonous. If you get a flowering stalk, cut it off.

Question: I just noticed that one of my rhubarb plants is sending up a flowering stalk. Does this hurt the plant? Should I cut it off. Does it mean the plant will die? What, if anything, should I do?

Answer: Rhubarb flowering stalks should be promptly pulled and discarded if you want to keep the plant in good production. The flower stalks take a lot of energy to produce, thereby they reduce plant vigor and next year's production.

Flower-stalk formation in rhubarb can be caused by drought, not enough fertility and extreme heat. Older plants (especially older than about five years) tend set flowering stalks more than young ones.

Discourage flower formation with regular water (once a week) in the summer; good fertility (with compost or ferilizer); and mulching around the base to keep soil cool and moist.

For the highest yields of rhubarb stems, fertilize your plants three times per year. Apply 2 to 3 inches of composted manure, compost or ½ cup of an all-purpose garden fertilizer, such as 10-10-10, around each plant in early spring (now). Once growth starts to occur, apply fertilizer again. And then, in the fall, mulch your plants with 6 inches of compost or composted manure and leaves.

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Rhubarb plants produce well for several years, if they are divided every three to five years. Rhubarb suffers from relatively few pests. With good sanitation, soil aeration and crop rotation, diseases can be largely avoided.

The best time to dig and divide large, old rhubarb plants is in early spring or late summer. Do it soon or wait until September. When you split up the plant, make sure there is at least one strong bud. Plant your new plant in full sun to partial shade in deeply worked rich soil with plenty of organic matter. Throw in some high-nitrogen fertilizer when planting. Two plants is probably enough for most households. After planting, water slowly and deeply, if needed. Mulch with compost or other organic materials.

If you have new plants, refrain from harvesting your rhubarb the first year after planting. Each plant needs time to build up food reserves in the root to produce thick, robust stems.

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Starting the second year, harvest the older leaf stalks by grasping them at the lower end, close to the main part of the plant. Pull down and to one side so the stalk snaps off clean. Never harvest all the leaf stalks off a plant — it depletes the plant's food reserves.

Only the stalks of rhubarb are edible. Rhubarb leaves contain oxalic acid and other harmful compounds, which cause severe damage to your mouth and digestive system if eaten. It  can cause illness or death if eaten in large amounts. Remove the leaves from the stalks immediately after harvest. The leaves can be composted as the calcium oxalate breaks down in the composting process.

Late June, it is best to stop harvesting rhubarb stems and let the plant just grow, make lots of leaf area and store food for next year. The leaf stalks become mealy by mid-summer anyway, not that good for eating, in my opinion.

Here’s a trick for getting harvestable rhubarb extra early each year. Cover mature plants with clear plastic in the early spring, before the crown starts to grow. As growth starts, cut ¼-inch diameter ventilation holes in the plastic. As leaves get larger, cut the plastic to allow the leaves to grow free.

Harvested rhubarb stalks can be kept in the refrigerator for two to three weeks or frozen for longer storage. This tart vegetable, often eaten as a fruit, contains vitamin C and can be used in pies, as a stewed fruit or in sauces for meats or poultry. If cooked with sweeter fruits such as strawberries or apples, rhubarb requires less sweetening. Unlike many vegetables (yes, it is a vegetable, not a fruit in the botanical sense), you can dice and freeze rhubarb stems raw without peeling or blanching.

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