Rhubarb

Asked June 9, 2015, 3:24 PM EDT

Client stopped in with rhubarb leaves. The leaves have brown spots on them and turn yellow. The stalks grow thin and die young. Client uses lake water for watering. What is wrong with the plant? What recommendations do you have?

Lake County South Dakota

1 Response

I don't have an answer for you, but will send an article on growing rhubarb and the person can see how their cultivation practices compare:

Planting and Care

Rhubarb is generally purchased as crowns or divisions, rather than propagated from seed. Purchase rhubarb crowns from a local nursery, garden center, or from seed catalogs. Plant the crowns as soon as possible so they don�t dry out. Rhubarb crowns are best planted in early spring when the roots are still dormant or plants are just beginning to leaf out. Rhubarb can also be planted in the fall after dormancy has set in.

Each plant will require approximately one square yard of space. Loosen the soil to a depth of 10 inches. For each plant, prepare the soil by adding 3 to 4 inches of compost or well-aged manure and a handful of fertilizer that is relatively high in phosphorus and potassium, such as 5-10-10.

Cover the crowns with no more than an inch or two of soil. Planting rhubarb crowns too deep will delay production. Press the soil firmly around the roots and water well. As soil and air temperatures begin to warm, new buds will push up through the soil.

Once the plants are up and growing, the addition of a 3- to 4-inch layer of clean straw, compost, or similar mulching material will help control weeds and conserve soil moisture for plant growth and development. Flower stalks should be removed as they appear, as they deplete reserves from the crown that supports vegetative growth.

Rhubarb, like most vegetables, requires regular irrigation during dry weather. Keep the soil moist but not soggy. Rhubarb requires annual applications of fertilizer for good growth and continued production. Fertilize each plant with a handful of a 5-10-10 fertilizer in the spring. A midsummer fertilizer application will also benefit these vigorous plants.

Harvest

In order for the plant to become well established, leafstalks should NOT be harvested the first year and only a few the second year. From the third year on, rhubarb is harvested in late May and throughout June in Ohio. Stop harvesting leafstalks when the plant begins to produce slender stalks, a sign that its reserves are low.

Never harvest more than one-third to one-half of the plant�s stalks, in order to preserve enough foliage to sustain the crown. The stalks are most flavorful when fairly young, so harvest them soon after the leaf expands. Harvest by grasping each leafstalk near the base and pulling it slightly to one side. Stalks can also be cut with a knife.

Fresh rhubarb can be stored for two to four weeks at 32-36 degrees F and 95% relative humidity. Store in perforated polyethylene bags in the refrigerator crisper drawer for best results.

After the last harvest in early July, the plants should be allowed to grow until killed by frost. After the tops are dead and the ground is frozen, the plants can be covered with 2 to 3 inches of straw mulch. Remove one-half of the mulch before growth starts in the spring.

Rhubarb leaves may be added to your compost pile. While the leaves contain oxalic acid, this rapidly decomposes in the compost pile and has no negative effect on the quality of the compost.

Frost Damage

If rhubarb is hit by a hard frost or freeze in late spring, it still can be eaten provided the stalks are firm and upright. Leaf injury would appear as brown or black discoloration along the margins. If the stems are soft and mushy, don�t eat them. Severe cold injury may cause the oxalic acid crystals in the leaves to move into the stalks, increasing the chance of poisoning. If in doubt about the safety of eating the stalks, don�t. Cut the damaged stalks off and compost them. Allow new stalks to develop for eating.

Pests

Pests are usually not a problem on rhubarb in the home garden. However, the rhubarb curculio, a rusty snout beetle about 3/4 inch long, can, on occasion, cause serious damage to the leafstalks. Curly dock is an alternate host for this insect, so dock plants nearby should be removed. Treat the base of curculio-infested rhubarb plants with a pesticide recommended by your OSU Extension county office or on the Ohioline website at http://ohioline.osu.edu.

Crown rot is a disease that can be a problem in commercial production, but it too is seldom seen in the home garden. Rhubarb crown rot is caused by Phytophthora species fungi. Symptoms include plants that fail to leaf out in the spring, or they may leaf out only to die abruptly. Upon digging the plants up, the roots and crowns are rotted. Fungicides have not been found to be effective in eliminating the problem. The best control is prevention, by planting purchased rhubarb crowns, rather than getting starts from a neighbor, and planting in well-drained soil. I hope this helps.