Making Good Garden Soil

A garden is only going to be as good as its soil quality, which is why we gardeners are obsessed with building better soil. Many of us are not blessed with perfect soil where we have planted our gardens. We also do not have the luxury of an endless gardening budget, allowing us to bring in fine garden loam by the dump truck load. And even if we could afford that, trucks driving from miles away, compacting the soil when they unload the loam, and digging up the soil from prime agricultural land is not exactly the definition of “sustainable”.

Instead we choose the longer road to good soil that often comes with some combination of composting food waste, adding mulch material, using the occasional soil amendments and turning in loads of manure. In the case of my Portland garden, a steady supply of chicken manure-filled straw, dead leaves and composted food waste made a big difference over the last few years. Now that the chickens have moved south with me to Eugene though, the soil has been sitting without much attention and I worry it will decline over time.

In an ideal world, proper garden soil looks something like this: 25% air, 25% water, 45% soil and 5% organic matter. It feels spongy, has a rich brown color and smells like good earth. The air is important in the soil because it creates a space to retain water, offers a place for micro organisms to live in and provides them with needed oxygen. Water in soil feeds the micro organisms and makes itself available to plants when needed. A good soil ratio would be 40% sand and 40% silt, for drainage and stability, and 20% clay.

Vegetable gardeners can aim for higher than 5% micro organisms, but this is a good starting place for good garden soil. Micro organisms serve a very important purpose in the garden because of their mutually-beneficial relationship with plants. In this underground world, the bacteria and fungi that are called “micro organisms” collect valuable plant nutrients within the soil. Meanwhile, plants are collecting sugars through the process of photosynthesis. The micro organisms visit the plant roots and the two make a swap – the plant gives the micro organisms “food” in the form of sugars and the micro organisms give the plant nutrients collected from the soil. The stronger your community of micro organisms, the more your plants will thrive.

The simplest way to improve soil quality is to add organic matter to the soil. This can be in the form of fully broken down compost or organic materials that will be allowed to compost in place over time. Micro organisms are given something to munch on and the material creates air pockets and helps with water retention.

Knowing my soil in Portland needed some attention, I decided to make a call to the City of Portland to get a truckload of organic material in the form of free leaves. They delivered the load in a couple days and it took up the entire driveway! Like an insane woman, I decided it would be a really great idea to wrap up the end of the exhausting grad school term by spreading these leaves in one short day before flying to NYC. What was I thinking? I was so tired by the end that I could barely walk, but after eight hours of back-breaking work on a 17 degree day I was done.

The leaf layer sits anywhere from 6-12″ above the soil right now, looking like a big fluffy mess, but come Springtime it will sink to about 1/4 of its current size. Hard rains will help with the decomposition over the next few months and my fruit trees will be thanking me for the extra insulation from cold weather or blistering hot summer days. As it breaks down, it should make a clearer visual distinction between the pathways and planted areas.

If I had the means, I would certainly have loved to add a nice layer of manure in before those leaves, but alas budget and time doesn’t allow for that this year. Although the gardening season is over in the sense that we aren’t growing a lot right now, these are the days to build that soil!