The Joy and Science of Compost

I turn my face up to the sun, feel its solid heat. Wiggle my toes deeper into the lush grass and the warm soil beneath. June is an exciting month north of the 49th parallel. Spring’s cool fingers are finally loosening their tenacious grip.

In the garden I’m seeding herbs, transplanting potted tomatoes and looking forward to fragrant late summer harvests. All I see at the moment are fragile young shoots and leaves, but they promise to burst into action during June’s longer, warmer days. With that explosive growth in mind, this is a great time to think about providing plants with the nutrients they need to thrive over the summer.  

Plant health is a reflection of soil health. Healthy soil is rich in organic matter, which contains nutrients like nitrogen, phosphorus and potassium as well as beneficial bacteria and fungi. Organic matter also contains carbon compounds that contribute to good soil structure, so soil has better water retention during the summer and, paradoxically, better drainage when it’s wet. Basically, organics make for healthier soil all around, which makes for more productive, resilient plants.

A common and effective way to improve soil health is by adding compost. Compost contains organic matter and millions of microorganisms which break that organic matter down into nutrients that are available to plants. “Finished” compost - which has been completely broken down and contains the most available nutrients - is dark brown, crumbly, and smells sweet and earthy. Unfinished compost smells sour and may contain recognizable scraps of whatever went into the compost pile; adding unfinished compost actually uses up valuable nitrogen in the soil, because those hardworking microorganisms use nitrogen in their decomposition process.

The ideal time to add compost is either in the spring before planting, or in the fall in anticipation of the next season. I like to add a 1 to 2” thick layer and work it into the soil before planting, or mix a scoop of compost into each hole when I transplant from pots. If I don’t get to it before planting, I’ll put a layer of compost on top of the soil like mulch; it will incorporate into the soil over time. “Hot” (nitrogen-rich) compost can burn plants, so when I use the mulch technique I keep it about 6” back from their stems.

My favourite technique for a mid-season soil pick-me-up is making compost tea, which is exactly what it sounds like: compost steeped in water and applied as a liquid. In this case, the focus is on extracting the beneficial bacteria and fungi in the compost. An internet search of “compost tea” will turn up numerous recipes; some involve aerating the tea with a fish tank bubbler, others include specific additives such as molasses or kelp meal. Personally, I like a simple approach: fill a five-gallon bucket with rainwater (chlorinated water will kill our microorganism friends), add a big scoop of finished compost, and stir your witches brew twice a day for one week. Strain out the solids and you’ll be left with a deep brown, microorganism-rich liquid which can be poured around the roots of your plants to inoculate the soil, or diluted and applied to the leaves with a spray bottle as a foliar feed. I’ve worked with farmers who swear by the foliar feed technique as a way to boost plants’ immune systems against mildew and disease; I prefer the simplicity of the soil drench method. Either way, it’s the garden equivalent of taking a probiotic supplement - your plants will thank you.