Master gardening: How to replenish soil at the end of summer
Garden plants have depleted many of the soil nutrients by the end of summer, so we need to replenish them for our next plantings. Chemical fertilizers have environmental concerns so we usually use cover crops such as the legumes, clover, alfalfa, buckwheat or beans to fix nitrogen in the soil.
The mature crops are cut or killed and the old plants and decaying roots add nutrients and organic matter. Phosphates are provided by compost, greensand, rock phosphate or wood ashes. Other additives might be seaweed, fish emulsion, dried blood or bone meal. Ground eggshells or oyster shells can provide calcium, ward off slugs, and prevent blossom end rot in tomatoes. Dried grass clippings are a valuable addition as mulch around plants eliminating the bare soil that allows weeds to grow.
There are some deep rooted plants, often weeds and known as dynamic accumulators, that pull up nutrients from deep in the soil and store them in their leaves. We can use those leaves to add the nutrients to other plants. In a previous article, I mentioned that mullein grows in waste places where other plants cannot grow. It brings the nutrients to the surface allowing other plants to thrive; then wastes away leaving a fertile area behind. You may also have heard about plants that accumulate toxins like heavy metals. They are used to clean up contaminated waste sites.
There are many "dynamic accumulators," including dandelion, plantain, chickweed and stinging nettle. The most popular one is probably comfrey. Russian comfrey (symphytum uplandicum) is a European native sometimes referred to as "knitbone." The allantoins contained in comfrey cause cell growth, wound healing, and resolve a multitude of health problems, resulting in widespread use as an herbal remedy. However, it also contains alkaloids that were found to cause severe liver damage and cancer. The FDA has since banned the internal use of all comfrey products. It is not toxic to animals and is still used as fodder.
Originally a food plant and medicine, comfrey is now valued as a fertilizer as it adds nitrogen, magnesium, potassium, iron, calcium and selenium to our plants. It also provides organic matter because it contains little fiber and breaks down quickly.
The leaves provide more potassium than compost or manure. They can be added to compost to speed up the process or added directly to the plants as a mulch or into the planting hole. Add leaves to the potato trench for increased production. Leaves in the worm compost bin will yield more and larger worms. Leaves added to leaf mold in a bag will produce a good potting mix within a few months.
A liquid fertilizer can be made by placing fresh comfrey in a barrel and covering it with water. Cover it and your comfrey tea will be ready in a few weeks.
Comfrey is easy to grow in poor soil in a sunny location. Flowers are sterile so it does not self-seed, but it grows rapidly from root cuttings—so don't add them to your compost. Propagate by root division. Plants may be cut back to the ground monthly to harvest leaves.
Vi Stailey is a York County Master Gardener, a volunteer for Penn State Cooperative Extension. For more information, contact the Master Gardener office at 717-840-7408.