Comfrey (Symphytum officinale) is prized by gardeners for its ability to function as a dynamic nutrient accumulator. Its deep taproot system, which can extend several feet into the soil, allows the plant to draw up micronutrients often unavailable to shallow-rooted food crops. The leaves are particularly rich in potassium (K), which supports flowering and fruiting, along with nitrogen (N) and phosphorus (P). This unique biochemical composition makes comfrey an excellent, sustainable resource for creating potent, homemade plant fertilizers.
Preparing Comfrey Leaves for Processing
Proper harvesting maximizes the nutrient density of the foliage. The best time to cut the leaves is just before the plant begins to flower, as nutrient concentration is at its peak during this pre-bloom stage. Select the larger, mature lower leaves, leaving the smaller central growth to allow the plant to quickly regrow. Harvesting requires sharp shears or a knife, and wearing gloves is recommended because the leaves and stems have small, irritating hairs.
Once harvested, the processing method determines the next step. For concentrated liquid feed, the leaves must first be reduced by allowing them to wilt slightly in the sun for a few hours. This wilting removes excess water content, making packing the leaves into a container for fermentation more efficient. Use non-metal containers during all preparation and processing stages to prevent chemical reactions that could degrade nutrient quality.
Making Concentrated Liquid Feed
The concentrated liquid feed, often called comfrey “tea,” is produced through anaerobic decomposition that extracts soluble nutrients. Tightly pack the wilted comfrey leaves into a sealable container (e.g., a bucket or barrel), leaving minimal air pockets. Compress the material heavily, perhaps using a weight, to ensure maximum compaction and initiate breakdown.
As the leaves break down without oxygen, they release a dark, viscous, nutrient-rich liquid that collects at the bottom. This potent concentrate is notably pungent, requiring the container to be placed in a well-ventilated area away from living spaces. Containers equipped with a spigot near the base are useful for draining the accumulated liquid without disturbing the decomposing leaf mass.
Decomposition typically takes four to six weeks, depending on ambient temperature; warmer conditions accelerate the breakdown. Once the liquid has accumulated and the leaf material has reduced in volume, strain the concentrate through a fine mesh to remove solid matter. The resulting liquid is highly concentrated and stable for storage, providing a powerful, soluble boost of potassium and other minerals.
Creating Slow-Release Mulch
An alternative, less labor-intensive method uses the leaves as a solid, slow-release fertilizer directly in the garden. This “chop-and-drop” technique requires no fermentation or complex processing. Freshly harvested or slightly wilted leaves are laid on the soil surface around target plants, especially heavy feeders like tomatoes, squash, or potatoes.
As the leaves decompose aerobically on the soil, they slowly release nitrogen, phosphorus, and potassium into the topsoil layer. This natural breakdown provides a steady supply of nutrients over several weeks, which is gentler than a liquid feed application. The layer of leaves also acts as an effective weed barrier, suppressing weed growth and helping the soil retain consistent moisture levels.
Proper Application and Dilution
The concentrated liquid feed requires significant dilution before application to prevent damage to plant roots and foliage. A standard dilution rate is one part concentrate mixed with ten to fifteen parts of clean water. Applying the undiluted concentrate, which is rich in salts, can cause fertilizer burn, especially in young or tender plants.
This diluted feed is best used as a supplemental fertilizer during active growth, particularly when fruit or flower development is beginning, due to its high potassium content. When utilizing the slow-release mulch, apply the leaves in a layer two to three inches thick around the base of the plant, ensuring the material does not directly touch the stem. Replenish this mulch layer every four to six weeks as the older material breaks down and integrates into the soil.