Why We’re Not Fans of Amending Soil

There are many garden practices that are so widely believed and preached that they become de facto blanket statements for what makes a successful garden no matter where you live. From fertilizing to mulching to soil amendments, it may be that you’re doing too much when you don’t have to do hardly anything.

Let’s take amending soil. There’s this idea that there is only one good garden bed — one composed of loose, crumbly, earthy-smelling black gold. When we’re talking ornamental gardening nothing could be further from the truth (however, vegetable gardens do usually require a “perfect” bed). Even if you stop to think critically about where you find this information, you should start hearing some alarm bells. It’s companies, businesses, and products that need you to buy more. Hardware stores get truckloads of bagged topsoil and amendments each spring and stack them up in the parking lots enticing you. Landscapers increase their bottom line by offering additional improvements in the form of soil conditioners, top soil, wood mulch, fertilizer, etc. But most often you don’t need all of that. Here’s why amending soil isn’t as big of a deal as you think.

1) The perfect or ideal soil is the soil you have right now.Unless your land is poisoned or there are drainage issues undermining a structure, amending soil is often an expensive and back-breaking practice for homeowners (soil tests can tell you a lot, by the way). There are a plethora of plants from around the world — and of course lots of native plants, too — that will thrive in sandy, gravelly, rocky, loamy, mushy, or clay soils. In fact, by plethora we mean hundreds available to you right now in the nursery trade. A garden designer or landscaper worth their salt will know these plants and be able to match them to you site. And amended garden areas aren’t usually that big or deep; what does a plant think when it hits the native soil beyond its perfect little princess zone? “Uh, no thanks, I’ll just stay right here.” In the case of perennials this may inhibit their drought tolerance, and for large trees it will increase their likelihood of falling over in a windstorm because they didn’t root out far enough to anchor in.

2) Matching plants to site often means less maintenance and less plant death over time. The goal in any thriving garden is to have healthy plants. Traditional landscaping says that to do this you need to enrich the soil, add fertilizer, and apply lots of wood mulch. Now, there’s nothing bad about a one-time topdressing of compost (an inch) and a layer of mulch (usually an inch or two is plenty, especially for clay soils). These additions will naturally improve soil over time from the top down. But plant roots do that, too. Take native prairie grasses, which lose up to 1/3 of their roots every year. Those dead roots amend soil naturally as they break down and soil organisms digest them, while opening pathways of air and water. The plants that do the best are the plants that evolved to thrive in your site conditions — from sun to drainage to soil.

3) Matching plants to one another. There’s more to know about plants than the soil, light, and moisture levels they evolved in. There’s also the art of designing plant communities. A plant community is one with balance where plants naturally support and even compete with another over time to create a healthy and ecologically-sound landscape. Simply put, when we match plants to one another we increase the plant’s ability to be healthy. For example, planting taprooted plants among fibrous-rooted plants means no one is competing for resources at the same level. Or using behaved clumpers together (play nice, kids, and everyone will get a turn) or aggressive thugs together (butting heads means everyone keeps the other in check and no one wins out but they all work together for a common good — or how government is supposed to work).

4) Planting tightly means more soil building and less work long term. Our gardens are designed by planting material 12″ on center. Generally, we’ll use a base layer — a grass or sedge — that forms a living green mulch so you never have to use wood mulch again. Then we build the garden layers. First, we’ll add some spreading groundcovers like wild geranium or purple poppy mallow to fill in the gaps. Second, we’ll build up to the intermediate layer by using plants that get 2-4′ tall. Often, this second layer will compose plants of various foliage types, and we’ll use some plants with thicker foliage to help shade the soil, which contributes to out competing weeds and conserving moisture (plus it looks good to us and wildlife using the space). Finally, plants are left standing all winter; they’ll gather wind-blown leaves which will fertilize and build soil naturally from the top down like compost. And in spring, when the plants are cut down, they are placed back on the garden bed to provide the nutrients plants need while acting as a temporary mulch.

All of these practices — from matching plants to the soil and site and to one another, layering of the root zone and top growth, and leaving spring cuttings in place — is all the the soil amending you’ll ever need to do. And the only thing it will cost you is the price of plants, which you were in for anyway, and rethinking traditional high-maintenance practices. Do you see prairies and woodlands bring soil amendments, fertilizers, and wood mulch in bags and dump trucks? What can we learn from nature about creating resilient and sustainable landscapes that look pretty to us and wildlife?