Rhubarb is a long-lived perennial vegetable known for its heavy feeding habits. The plant produces material from early spring until summer, rapidly depleting the soil’s nutrient reserves. Proper and timely fertilization is fundamental for maximizing the yield of thick, tender stalks while ensuring the plant remains healthy for many seasons of harvest.
Rhubarb’s Primary Nutritional Requirements
Rhubarb’s nutritional demand focuses primarily on Nitrogen (N), which supports the development of the large leaves and succulent stalks that are harvested. A consistent supply of nitrogen fuels the rapid cell division and expansion necessary for vigorous above-ground growth each spring. Insufficient nitrogen results in thin, spindly stalks and reduced overall yield.
The plant also requires Phosphorus (P) for the development of a robust and deep root system, which is necessary to anchor the large crowns and support the perennial nature of the plant. Potassium (K) plays an important role in overall plant vigor, disease resistance, and regulating water and nutrient movement. Rhubarb thrives in a slightly acidic to neutral soil environment, ideally between pH 6.0 and 7.0, which ensures major nutrients are readily available for efficient absorption.
The Best Organic Soil Amendments
Organic amendments are beneficial for rhubarb because they release nutrients slowly, providing a steady food source while also significantly improving soil structure and water retention. Well-rotted manure (cow, horse, or chicken) is often the best organic feed, as it is rich in nitrogen and organic matter. Avoid fresh manure, which can burn the plant’s roots due to its high salt content and rapid nitrogen release.
High-quality compost also works well, providing a balanced mix of micronutrients and organic material that supports beneficial soil microorganisms. These materials function as a slow-release fertilizer, feeding the plant throughout the growing season as they break down. Apply a generous layer of one to two inches of aged manure or compost around the base of the plant in early spring, just before new growth begins.
Applying these organic feeds as a top dressing or side dressing helps avoid disturbing the shallow crown and roots of the established plant. A second, lighter application can be beneficial immediately after the final harvest of the season to replenish the nutrients used during the main production period. For a rapid nitrogen boost, organic supplements like alfalfa meal or blood meal can be side-dressed in the early spring to quickly stimulate leaf and stalk growth.
Choosing and Applying Synthetic Feeds
For gardeners preferring a quick, targeted application, synthetic granular fertilizers offer a straightforward way to meet rhubarb’s high nutrient demands. The most recommended synthetic formulations are those that are balanced, such as a 10-10-10 NPK ratio, or slightly nitrogen-heavy. A balanced blend ensures that while nitrogen is the focus for stalk production, the plant still receives adequate phosphorus and potassium for root health and overall vigor.
A typical application rate for an established rhubarb plant is about one-half to one cup of a 10-10-10 granular fertilizer per plant. This fertilizer should be applied in a circle around the plant, extending out to the drip line of the foliage, but avoid placing the granules directly onto the plant’s crown. Direct contact with the crown can cause chemical burn and damage the perennial growth point.
The timing of application is crucial for maximizing the benefit of synthetic feeds. The first feeding should occur in early spring, as soon as the ground is workable and before the new stalks begin to emerge. A second application can be made immediately after the final harvest, typically in mid-to-late summer, to help the plant store energy and nutrients in its crown for the following year’s growth. Over-fertilization, especially with high-nitrogen synthetic products later in the season, should be avoided, as this can encourage soft, weak growth that is more susceptible to winter damage.