Wool for the Soil
Updated: 5 days ago
Wool helps solve two big challenges for Wyoming farmers and gardeners - soils that don’t hold enough water, and soils that are low in organic carbon.
What makes wool so special?
Wool holds 3-4 times its weight in water - just what you need when you are growing food in the desert. Not only does wool hold water in the soil and reduce watering frequency (especially in small containers), it also absorbs water from the atmosphere thanks to something called polar-peptide bonds. That's better than cloud seeding!
Wool is made of a fibrous protein called keratin. Compared to most other organic fertilizers, including compost and manure, wool is very high in nitrogen, potassium, and sulfur. At 7-9% nitrogen, it provides twice the nitrogen as chicken manure (3-5%) and almost as much nitrogen as blood meal (12%). Most compost is less than 2% nitrogen.
Perhaps most importantly, wool is loaded with active carbon (>35%). More than compost, and more than most organic fertilizers. Active carbon is the driver of the soil system. It provides the energy for soil microbes, and is the base for stable organic matter in the soil. Wyoming soils are very hungry for organic carbon!
Wool feeds keratin-degrading microorganisms. This means that wool helps support bacteria and fungi in your soil that eat specific plant pathogens like the one that causes damping off in seedlings, black rot in potatoes, and root rot of sugar beets. These same beneficial microbes also produce plant growth promoting hormones as they decompose the wool.
How to use wool
While there is some variability based on the source of wool, the approximate “fertilizer value” is 9-0-5. Notice that it does not contain any phosphorus. This means you may need to add other sources of phosphorus to your soil like bone meal or manure compost.
Raw fleece can be used as a surface mulch, buried in raised beds, placed in the bottom of transplant holes, or mixed into potting soil for flower pots and hanging baskets. There is even some evidence that wool on the surface of the soil deters slugs, snails, and some insect pests.
Raw pellets work best incorporated into the soil or placed with seeds and transplants. While wool does not need to be pelletized, the pellets are easier to handle and mix with soil. The heat and pressure of the pelletizing process also seems to kill any seeds that might be in the fleece.
Wool decomposes slowly over several months to years, depending on the soil type and microbial activity. If adding into raised beds, or incorporating into your garden soil, or using as a layer in sheet mulching, it is best to add in the fall. In the spring, put wool in transplant holes, in row with the seeds, and use it as a mulch.
Wool can be added to the soil anytime, but for best results, add wool in the fall to allow time for microbial decomposition.
Start with ~ 1/2 of a cup of wool pellets per gallon of soil for house plants and flower pots. This will help hold water and provide nutrients.
Place a few pellets or a bit of raw fleece around the roots when transplanting, or in the trench with seeds when planting.
Incorporate pellets into garden soil and raised beds at a rate of ~ 1lb per 30 square feet.
Use wool as a mid-layer in sheet mulching.
Too much of a good thing
Healthy soil needs plenty of food, water, and air. Too much wool makes for soggy soil which means not enough air, and unhealthy plants. This is easy to do in small containers, especially if you do not adjust your watering frequency to account for the wool.
A thick layer of fleece as mulch on top of the soil in an area that is watered frequently with an overhead sprinkler can also cause problems with overly saturated soil. This is more likely to happen in clay soil than sandy soil.
Field research
In a farm trial in Ohio, tomato and sweet pepper beds mulched with wool yielded 64% and 67% more than beds mulched with hay.
In a University Vermont research trial, average fruit size for tomatoes was significantly larger using wool pellets compared to the standard (equivalent) fertilizer rate. Broccoli plants treated with wool pellets grew more vigorously and were ready for harvest 3 days earlier than the control group.
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