Rhubarb is a perennial plant often treated as a fruit in the kitchen, but it is botanically a vegetable valued for its tart stalks. While rhubarb is naturally hardy, providing it with proper care during the winter months directly supports its health and ensures a productive harvest the following spring. Preparing the plant for its dormant period is a simple process that addresses both protection from the elements and the potential for an earlier yield.
Essential Winter Preparation Before Dormancy
Winter preparation begins after the first hard frost causes the foliage to die back naturally. Once the leaves have withered, cut them back near the ground. Removing this material eliminates potential overwintering sites for pests and fungal spores that could harm the dormant crown.
After clearing the dead leaves, the area surrounding the plant should be thoroughly weeded to reduce competition for nutrients and moisture in the spring. A light layer of organic material, such as well-rotted manure or finished compost, can then be spread directly over the crown. This application replenishes soil nutrients used during the growing season and offers a mild, initial layer of insulation.
This basic layer of mulch should not be thick; its primary function is to feed the soil and offer minimal protection before the deepest cold sets in. The plant requires a period of cold dormancy, known as vernalization, to trigger robust growth when temperatures rise again.
Determining If Protective Covering Is Necessary
Rhubarb is remarkably cold-tolerant, capable of surviving in regions as cold as USDA Hardiness Zone 3. The crown, where new growth buds reside, is naturally insulated by the soil and root system. Gardeners in Zone 5 and warmer find that the routine mulching done during preparation is sufficient protection.
Heavy protective coverings are usually reserved for specific situations, such as newly planted crowns that have not established deep roots. They may also be needed in colder, borderline zones, or during periods of extreme cold when a deep freeze occurs without a natural insulating layer of snow.
In these instances, a thick layer of shredded leaves or straw can be piled over the crown to prevent the ground from freezing too deeply, which could damage the root structure. This heavy covering is purely for insulation against deep cold, distinct from the lighter organic mulch used for soil enrichment. Once the threat of severe, prolonged cold has passed, this material should be removed to prevent the crown from becoming too warm and rotting.
Using Covering Techniques for Early Harvest
A different reason for covering rhubarb is forcing, which stimulates the plant to produce tender stalks ahead of schedule. This technique relies on excluding light and trapping residual soil warmth to break dormancy early. Forcing should only be attempted after the plant has experienced sufficient chilling hours, usually after January, ensuring the dormancy cycle is complete.
The most effective materials for forcing are dark, opaque containers like specialized rhubarb forcing pots, large buckets, or barrels placed directly over the crown. These covers trap the slight warmth radiated by the soil and prevent light from reaching the emerging shoots.
The lack of light inhibits chlorophyll production, resulting in the desired pale, pinkish-red stalks that are notably sweeter and more tender than sun-grown rhubarb.
Forcing demands a significant energy expenditure from the plant. To maintain the long-term health of the rhubarb patch, this technique should not be performed on the same crown every year. Gardeners should rotate the forced crowns, allowing each plant to recover for at least one or two seasons before being subjected to early stimulation again. The stalks are typically ready for harvest six to eight weeks after covering, providing an early taste of spring.