Rhubarb is a hardy perennial vegetable prized for its tart stalks. As a heavy feeder, it requires significant nutrients to sustain its vigorous, leafy growth. Providing the right nutrition is important for maximizing the thickness and quantity of the harvested stalks. Understanding when to feed your rhubarb is as important as knowing what to feed it, directly impacting its productivity and longevity.
The Critical Timing for Established Rhubarb
The most important time to feed established rhubarb is in the very early spring, just as the ground begins to thaw or new growth emerges. This initial application powers the plant’s aggressive growth cycle, supporting the production of large leaves and thick stalks for harvest. Timing this feeding before the plant actively starts growing ensures the nutrients are immediately available when the plant breaks dormancy.
A second, lighter feeding is beneficial after the main harvest period, typically concluding by late June or early July. The continuous removal of stalks depletes the plant’s energy and nutrient reserves in the soil. This mid-summer application helps the rhubarb replenish energy, rebuild its crown, and store carbohydrates, preparing it for winter dormancy.
It is important to cease all fertilization entirely after mid-summer, generally by the end of July at the latest. Applying nitrogen-heavy fertilizer too late encourages a flush of tender, new growth. This soft tissue is highly susceptible to damage from the first frost, which can weaken the plant crown before winter sets in.
Nutrient Needs and Recommended Fertilizers
Rhubarb is primarily a nitrogen-heavy feeder because the harvested portion is the leaf stalk (petiole), a vegetative part of the plant. Nitrogen (N) supports this lush growth, promoting large leaves and robust, thick stalks. While nitrogen is the main focus, a balanced approach ensures the plant has strong roots and overall vigor.
Many gardeners rely on organic soil amendments, such as well-rotted manure or compost, which are excellent choices for rhubarb beds. These materials provide a slow, steady release of nutrients over the season, which is beneficial for a perennial. Furthermore, organic matter dramatically improves soil structure, helping the dense rhubarb roots access air and moisture efficiently.
For gardeners preferring a synthetic option, a balanced fertilizer with an N-P-K ratio like 10-10-10 or 13-13-13 is recommended. This balanced formulation supplies equal parts of nitrogen, phosphorus, and potassium, supporting leaf growth, root strength, and overall plant health. Adjust fertilizer amounts based on the plant’s vigor, increasing the application if stalks are thin or spindly.
Initial Feeding and Soil Amendment Techniques
Fertilizing newly planted rhubarb crowns follows a different schedule than established plants. It is recommended to avoid applying heavy fertilizer at planting time or throughout the entire first growing season. This delay allows the young crown to focus on establishing a deep, strong root system before supporting vigorous stalk production.
Before planting a new crown, the soil should be amended by mixing in a generous amount of compost or well-aged manure to a depth of at least 10 inches. This pre-planting preparation creates a nutrient-rich, well-drained environment that sustains the young plant through its establishment phase. A light application of bonemeal can also be incorporated at planting to support initial root development.
When applying fertilizer to an established plant, spread the material around the plant in a circle, following the drip line of the leaves. Avoid placing the fertilizer directly onto the crown, as this can cause burning and damage the growing points. The fertilizer should then be lightly worked into the top few inches of soil before being thoroughly watered in.
Annual maintenance should include applying a thick layer of organic mulch, such as straw or compost, around the plants. This mulch acts as a slow-release feeder as it breaks down, suppresses weed growth, and helps maintain consistent soil moisture. Checking the soil pH every few years ensures the rhubarb can efficiently absorb the nutrients provided.