I recently started thinking about what I'm going to plant in my garden this spring — it's a nice mental escape from the current dreary New England weather — and as I've been researching different flowers and vegetables, I keep seeing references to "ideal soil quality." For example, the growing guides in Almanac always say things like, "Dahlias thrive in rich, well-drained soil. The pH level of your soil should be 6.5-7.0, slightly acidic."
It makes sense that soil has a pH, but it's never been something I took into consideration as I planted my garden. I've always considered soil quality to be "advanced gardener stuff" — after all, my plants grow just fine — but seeing repeated mentions of it has piqued my curiosity. As a result, I started reading about soil quality, plant pH, and soil testing, and eventually, even reached out to Vanessa Dawson, a gardening expert and CEO of Arber, an organic, non-toxic plant wellness company, for expert insights on soil quality and why it matters. Here's what I learned.
Does soil quality really matter?
Have you ever seen pictures of big, beautiful, flourishing plants and thought to yourself, "Why don't mine look like that?" If so, there's a good chance soil quality has something to do with it. Dawson explains that healthy soil yields healthy plants, and even if your plants are doing OK, chances are they could be better if you improved the soil.
"Soil provides a massive diversity of microbes, nutrients, and bacteria that plants are dependent on," explains Dawson. "When plants send out roots, they expect to find this complex microbiology that they can work with interdependently, both feeding the soil sugars and attracting then absorbing the necessary compounds they need through their roots." If they don't find the nutrients they need, plants won't grow as large and likely won't put out as many flowers or vegetables as they could.
What does "bad" soil quality look like?
Naturally, my next question was, "So how do I know if my soil is bad?!" Dawson explained that there are several factors to look at, including the appearance of the soil, how it absorbs water, and whether there are insects present.
"Soil that is light brown versus dark and black is often void of microbial diversity," she explains. "There should be a variety of different microorganisms in your soil. If you dig up a scoop, you should see worms and bugs and beetles — all beneficial insects helping to aerate and feed the soil keeping its microbiome thriving." She also noted that soil should absorb and hold water easily and that plants should be deep in color with long, spread-out root systems.
If you still aren't sure your soil is healthy, there are testing services that will give you a more concrete answer. "You can always send a sample of your soil to be tested," says Dawson. "Most state universities provide excellent and affordable soil testing services through a cooperative extension service."
What's the deal with soil PH?
There's also the matter of soil pH, a measure of how acidic or alkaline it is. "Soil pH runs on a scale from 0 to 14, with 7 being a neutral pH — over 7 is alkaline and under 7 is acidic," says Dawson. "Most plants and beneficial microorganisms prefer a pH between 6 and 7.5." The pH of soil affects how well plants can absorb nutrients, and while your plants won't die if the soil pH is a little off, they again might not get as big or put out as many blooms. Soil testing services will tell you the pH of your soil, but there are also soil pH test kits and soil pH meters that you can use at home.
If you discover that your soil pH is outside the optimal range, there are various additives you can use to get it back on track, but be warned: it's not a one-and-done task. "If you want to adjust pH organically, it needs to be done over time — it won't be an overnight fix," says Dawson. "Mulch, coffee grounds, and compost are all great ways to make your soil more acidic over time. Adding a dilution of baking soda and or crushed eggshells are two natural and gentle ways to make soil more alkaline over time." There are also commercial additives that will adjust the pH of soil — garden lime will increase the pH, making it more alkaline, while a soil acidifier will decrease the pH.
How to improve the quality of soil in your garden
If you've determined that your soil could use a little love, organic matter — aka some kind of decomposing plant and/or animal matter — is going to be your best friend. The OSU Extension Service explains that organic matter will help improve soil structure, water retention and pore space, all while adding key nutrients that plants need to thrive. The most common types of organic matter used in gardening are compost, animal manure, and mulch, but you can also use things like leaves and grass clippings from your yard.
To incorporate organic matter into your garden beds, you'll want to start by digging into the soil with a shovel or cultivator, turning the dirt over and breaking up large clumps to relieve any compaction. You can then add one or two inches of organic matter, whether it's aged manure or compost, and mix it into the top layer of the soil using your garden tool. Ideally, this should be done on a yearly basis, typically in the fall, as this will give the organic matter time to break down in the off-season. However, you can also do it in the spring a few weeks before you plant — bagged compost is best for this application, as it's already broken down. For more detail on this process, OSU has a comprehensive guide on improving garden soil with organic matter.
If it's going to be overly expensive or labor-intensive to modify your existing soil, another option is to build raised beds, which you can then fill with better growing material. "If you want to purchase additional soil, focus on organic products," says Dawson. "Look for products oriented towards professional growers, as the quality will be higher, and always look for a soil that contains a mixture of compost."
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