Rheum rhabarbarum

Rhubarb is an herbaceous, cool-weather perennial vegetable that grows from short, thick rhizomes. It produces large, triangular-shaped poisonous leaves, edible stalks and small flowers. The red-green stalks, which are similar to celery in texture, have a tart taste and are used in pies, preserves, and sauces.

The leaves contain the toxic substance oxalic acid, a nephrotoxic which is damaging to the kidneys and may be fatal in large amounts but generally causes shortness of breath, burning sensations in the mouth and throat, coughing, wheezing, laryngitis, and edema. If the leaves have been ingested do not induce vomiting but call the Poison Control Hotline. Oxalic acid will migrate from the leaves to the stalks of plants that have been exposed to freezing conditions, therefore those stalks should not be consumed.

Rhubarb has a wide range of acceptable pH, from 5.0-6.8 which makes it well-suited for a Connecticut garden. Have a soil test done through the UConn Soil & Nutrient Analysis Lab and follow the recommendations a year before planting if possible. Amending the soil with aged manure or well-rotted compost will increase plant production.

Rhubarb should be planted in an area with full sun or light shade where it will be out of the way, at one end or side of the garden, as it will remain productive for 5 or more years. They should be planted in an area with good drainage or in raised beds.

Rhubarb roots may be planted or divided in the early spring while they are still dormant. Dig up roots that are more than 5 years old to divide them. The appearance of seedstalks or flowers is a sign that the plant needs division. Cut each root into 4-8 pieces ensuring that each section has a new bud and at least 2” of root. Newly divided plants should be put into the ground as soon as possible. The crown bud should be 2” below the surface of the soil. Plants should be spaced 3-4’ apart in rows that are also 3-4’ apart. Remove flower stalks the first year.

Starting rhubarb from seed is not recommended as all cultivars are hybrids and the resulting plant will not be true to the mother plant.

Rhubarb is fairly drought tolerant as plants can store water in their fibrous root systems which run 12-18” below the surface. During extended periods of hot dry weather plants should be watered deeply so that the soil is damp to a minimum depth of 3-6”. Mulch will suppress weeds and retain water but do not cover the crowns.

Rhubarb requires little to no fertilizer although ¾ of a cup of a balanced fertilizer (10-10-10) applied once a year in a ring outside of the stalks will benefit production

Harvesting of rhubarb generally starts in mid-June. Do not harvest rhubarb stalks until the second year when stalks may be harvested for 1-2 weeks. After that, the full harvest period is 8-10 weeks. Pull the leafstalks off at the base by using a twisting motion and trim and discard the leaves. Wash the stalks well before using. Freshly harvested stalks can be refrigerated for a few days.

Fungal Leaf Spots
Fungal leaf spots is more of an aesthetic issue as they affect the leaves only. Avoid wetting foliage if possible by watering early in the day so aboveground plant parts will dry as quickly as possible. Do not crowd plants by spacing them to allow air circulation. Eliminate weeds around plants and garden area. Remove and destroy or discard affected plant parts. Rake and dispose of all fallen or diseased leaves and stalks at the end of the season.

Phytophthora crown rot 
This can be a problem in poorly drained soils.

Botrytis
Botrytis fungus causes leaf, stalk, and crown rot. This disease is common in areas where rhubarb plants do not receive proper air circulation and high humidity is present. Eliminate rotting material near the plants and apply a fungicide at 7 day intervals as soon as you notice the disease. Young plants and transplants tend to be more susceptible to diseases.

Rhubarb curculio
Rhubarb curculio, Lixus concavus, is a snout beetle that bores into the stalks, crowns, and roots of rhubarb plants. Feeding injury appears as notches on the stalks and leaf edges. The adult overwinters in debris near the rhubarb plants. They appear in mid-May to lay eggs in punctures that they make in the stalks of rhubarb as well as the alternate hosts of dock, thistle, and sunflower. The eggs laid in the rhubarb stalks get squeezed by the growing tissues and do not hatch. The removal of the alternate hosts from the area during July will reduce the populations. Adults can be hand-picked and destroyed.

Lesser pests include Spider Mites and Stem Borers.