April 6, 2016

Soil shepherding


This is the United Nations Year of Soils, so let’s talk about how we can treat soil better… and why. We’re learning a lot very quickly, and best practices are changing month by month. To till, or not to till? When, or even IF, to fertilize? What kind of mulch to use, if any? These are all important questions.

Cristina da Silva is a horticulturist and soil enthusiast, which has led her to start #groundchat, a tweetchat on soil-related topics on Twitter (Fridays at 2 p.m.) and to blog at therealgardener.com. When asked about tilling soil, she says, “Generally I would say tilling is a bad idea. Tilling breaks down soil structure. There are, however, times that tilling is appropriate. For example, surface soil crusting, or breaking up a hardpan. Do it once, and then start adding compost, mulch and/or growing ground covers to cover bare soil.”

So, tilling or turning of soil should now be a rarity. The whole soil micro-ecosystem is incredibly important to plant health. When we use cultivators or rototillers, we kill millions of beneficial bacteria and chop up the mycorrhizal fungi which help plants absorb water. These microbes enhance soil structure and health. They also have a role in making nutrients available to be easily taken up by plant roots. The better alternative to tilling is to mulch with organic matter such as composted pine mulch, and let the worms and insects work it into the soil naturally. It’s easier! In addition, not turning soil reduces erosion, which protects our waterways.

Build the soil naturally
We think a lot about fertilizing lawns and gardens, but if over-applied or done at the wrong time of year, this can contaminate runoff and pollute our rivers and lakes. Adding composted pine mulch is a better alternative since it provides all nutrients, not just nitrogen, phosphorous and potassium. Compost also increases fungal and bacterial populations. Promoting bacterial growth through composting actually releases the phosphorous that already exists in the soil, and there’s plenty of it.

Composted mulch (where pine bark or chipped hardwood is mixed with leaves and then turned to kick-start the breakdown process) or even just compost, is better than wood chip or bark mulch since it feeds the soil and the creatures that live in it. There is still debate about whether straight wood chips or bark used as mulch deprive the soil of nitrogen, since the bacteria that break down organic matter need nitrogen to survive, and wood is mostly carbon. Recent studies suggest that this is true only in the zone of interface between the mulch and soil, which suggests we should only be concerned in annual beds or vegetable gardens. Alternatively, just to be safe, simply mulch up leaves in the fall and spread them directly on the garden. 

Work with soil, not against it
Finally, old gardening text books usually start with a chapter on amending soil. This was recommended so we could plant whatever we wanted. Modern wisdom revolves around planting the right plants for your existing soil type. If you feel challenged by sandy, clay or even wet soil, there are amazing plant lists (easily found online) for each of those situations. Many plants love clay. For example, roses, coneflowers and ornamental grasses thrive in it. For sandy soil, go to any beach to see what does well naturally. Use Mother Nature as a guide. She’s been doing it longer than we have. Working with existing soil takes a bit of learning, but saves work.

When asked, “What’s the most important thing landscapers don’t know about soil that they really should?” Cristina replied, “I suspect many gardeners and landscapers are confused about soil texture and soil structure. You can’t change soil texture, but you can improve the structure of any soil. Yes, that includes clay. Don’t add sand. Just add compost. And it takes three years before you start to see any noticeable changes. The wait is totally worth it!”

The question, “What is the most exciting thing we’ve learned about soil?” was put to da Silva. She replied, “Land heals! That’s the most exciting thing I’ve learned about soil. We have the tools and techniques to make it work. Landscapers interested in remediating soil should pick up Leila Darwish’s Earth Repair. The book has a number of grassroots bioremediation techniques to heal soil.” 

When customers approach us for landscaping, the first request is “low maintenance.” The methods to protect soil mentioned here are less work than the old ways we’ve been taught. Protecting the soil protects our watersheds, helps plant health and even preserves our food security. It’s been said that it takes 100 years for nature to make an inch of soil, so it’s worth looking after. Once, we took it for granted, but we are finally waking up to how to work with soil. Learn all about which plants like your soil, and the soil on your customers’ properties. Now, go have fun in the garden. Yes, it’s a job, but it can still be fun.