You may have seen some home-sourced fertilizers on social media — things like compost tea, banana peels, and coffee grounds — being touted as an inexpensive alternative to commercial fertilizers.
Homegrown New Hampshire host Emma Erler, lead horticulturist with Kirkwood Gardens, says they don’t hurt, but recommends putting your effort into starting a compost pile instead.
Compost Tea?
Erler says compost tea is touted as a miracle solution for disease control and fertilization.
Essentially, compost or manure is placed in a permeable bag and submerged in a bucket of water until the water turns black. This solution contains nutrients and anaerobic microbes.
Is it worth brewing up a big batch of compost tea? Scientific evidence suggests probably not.
It has been shown to reduce the incidence of some foliar diseases in the lab; in the field there’s not a lot of good evidence. The composition of compost tea is highly variable so it’s difficult to study.
Erler says rather than spend time and money leaching material out of compost, just use compost as part of an organic mulch layer. Organic mulch has been shown to suppress disease, and mulched landscapes are usually healthier and look tidy.
Coffee Grounds?
Coffee grounds can be beneficial to the soil because they contain carbon, nitrogen, and other compounds that feed soil organisms. They also make an excellent addition to compost.
But Erler says they do not consistently lower soil pH. If that’s what you’re trying to do, use elemental sulfur instead.
Crushed eggshells?
Crushed eggshells are said to prevent blossom end rot in tomatoes. Blossom end rot is a sign of calcium deficiency in fruits like tomatoes, peppers, and zucchini. The idea is that adding eggshells will increase calcium in the soil.
Erler says eggshells decompose very slowly, generally too slowly to be effective. If you need calcium right away, she says agricultural lime and gypsum are better choices.
Banana peels?
Bananas have a lot of potassium in them, and plants need a lot of potassium. But a fresh banana peel that you throw into the garden doesn't have potassium in a form that's readily available to plants. It has to be broken down first by soil microbes, and they need nitrogen to do that.
If you put a banana peel in the garden by your plant, it is robbing the soil of nitrogen as that banana peel breaks down, meaning there will be less nitrogen available for plants that are greening up.
Erler says you’re better off composting the banana peel and top-dressing your plants with that compost.
How to start a compost pile
Erler says a cold compost pile is easy to start and maintain.
A hot compost pile needs frequent tending and turning, with the perfect ratio of carbon and nitrogen that cause it to heat up enough to pasteurize or kill pathogens and weed seeds.
But the composting process happens regardless. Erler says the sun exposure, the moisture, and exactly what you added to that compost pile are factors that determine how quickly the organic material breaks down.
“If you just have a leaf pile it could take several years to produce compost, but with a mix of leaves and kitchen scraps and grass clippings, even with a cold pile, you might have some decent compost within just a season.”
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See you in the garden!
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
