Best Rhubarb Fertilizer: When and How to Apply

Rhubarb requires consistent nutrients to develop the thick, flavorful stalks prized by gardeners. Providing the right nourishment encourages vigorous growth and supports the plant’s overall health, ensuring a productive rhubarb patch for years to come.

Best Types of Fertilizer for Rhubarb

Rhubarb is a “heavy feeder,” meaning it consumes a significant amount of nutrients from the soil to produce its large leaves and stalks. To support this growth, a balanced fertilizer is effective. Formulations with an equal ratio of nitrogen (N), phosphorus (P), and potassium (K), such as a 10-10-10 blend, provide a wide range of necessary nutrients. Phosphorus is beneficial for establishing strong, healthy root systems, which are the foundation of a long-lived plant.

Many gardeners prefer organic options for rhubarb, as they improve soil structure while providing nutrients. Well-rotted manure and garden compost are excellent choices that enhance soil moisture retention and add beneficial microorganisms. A one- to two-inch layer of compost or one to two shovels of aged manure per plant can supply a steady release of nutrients.

As an alternative to organic matter, synthetic granular fertilizers are also effective. These products offer a controlled and readily available source of nutrients. A balanced formula is a reliable choice. Some gardeners also supplement with specific nutrients like blood meal for nitrogen or bone meal for phosphorus if a soil test indicates a particular deficiency.

Rhubarb Fertilization Schedule

The primary time for fertilizing rhubarb is in early spring, just as new growth begins to emerge, providing the energy needed for a robust crop of stalks. For newly planted rhubarb, it is best to wait until the second year to begin fertilizing, especially if the soil was amended with compost at planting time.

A second, lighter feeding can be beneficial after the main harvest season has concluded. This application helps the plant recover and store energy in its roots for the following year’s growth. Avoid applying nitrogen-heavy fertilizers after the end of June. Late-season nitrogen can stimulate new, tender growth that may not harden off before winter, potentially damaging the plant.

Applying organic matter in the autumn is another effective strategy. Spreading a layer of compost or well-rotted manure around the base of the plants in the fall allows it to break down over the winter. This process enriches the soil, ensuring a nutrient-rich environment for the plant when it breaks dormancy in the spring.

How to Apply Rhubarb Fertilizer

The most common application method is side-dressing, which involves spreading fertilizer on the soil surface around the plant. Keep all fertilizers, including compost, several inches away from the crown and stalks. This prevents fertilizer burn and reduces the risk of rot.

For granular fertilizers like a 10-10-10 blend, use one-half cup to one cup per plant, distributed in a circle around its base. If you are using compost or aged manure, a one- to two-inch layer is sufficient. These amounts can be adjusted based on the size and vigor of your plant.

After spreading the fertilizer, gently work it into the top inch or two of soil with a hand rake. This makes the nutrients more accessible to the plant’s root system. Following the application, water the area thoroughly to dissolve the fertilizer and carry the nutrients down to the roots.

Signs of Improper Fertilization

Observing your rhubarb plant’s growth provides clues about its nutritional status. Over-fertilization, particularly with excess nitrogen, results in thin, spindly stalks and overly large leaves. While the plant may look leafy, stalk production will be poor.

Conversely, under-fertilized plants show signs of nutrient deficiency, such as stunted growth with weak or thin stalks. The leaves may also appear pale green or yellow, indicating a lack of nutrients to support healthy development. If you notice these signs, a soil test can help identify specific deficiencies.