Free and Low-Cost Ways to Feed Your Garden Without Buying Fertiliser

Fresh or recently buried banana peels don't release potassium quickly. Studies on fruit peel decomposition show that meaningful nutrient release into surrounding soil can take many weeks to months depending on soil temperature and microbial activity. Dropping whole peels beside plant stems can also attract pests. A better approach: add peels to your compost bin where they break down fully alongside other materials, contributing a modest potassium share to balanced compost.

The idea that coffee grounds are broadly beneficial is widespread but misleading. Research from Oregon State University Extension found that high applications of coffee grounds can suppress plant growth rather than encourage it. Grounds compact when wet, reducing soil aeration, and their pH effect — while real — is modest and variable. In soil that is already sufficiently acidic, adding grounds can push pH too low for most vegetables. Use them sparingly and mix them into compost rather than applying them directly as a top dressing.

Compost tea — made by steeping compost in water, sometimes with an aerator — has been promoted as a way to multiply compost's benefits into a liquid spray. However, independent reviews of the research, including assessments by university extension services, generally conclude that benefits are inconsistent. The microbial populations vary widely depending on compost quality, water chemistry, and brew time. Pathogen risk is also a consideration if the base compost was not fully cured. Solid compost applied directly to the soil remains more reliable and predictable than its steeped liquid derivative.

Wood ash is genuinely useful in specific situations — particularly in acidic soils (pH below 6.0) that need liming. It contains calcium carbonate, potassium, and trace minerals. But because it is alkaline, even moderate applications to neutral or already-alkaline soil can push pH above the range most vegetables tolerate, locking out nutrients like iron and manganese. Always soil-test before applying, use it sparingly (no more than about 20 lbs per 1,000 sq ft annually is a commonly cited guideline), and never use ash from treated or painted wood, which can introduce toxins.

Epsom salt has become a popular home garden remedy, often recommended for tomatoes and peppers. However, the Washington State University Extension and other land-grant university programs have noted that most garden soils already have sufficient magnesium, and adding more does not improve yields or plant health. In fact, excess magnesium can compete with calcium uptake, potentially worsening plant health. If you suspect a magnesium deficiency — typically visible as yellowing between leaf veins on older leaves — a soil test will confirm it before you treat.