Soil Proprietorship: The Plot Thickens
March 28, 2020
I’m making my own planting mix for backyard vegetables this year. What do you recommend?
- Carol B., Los Lunas
I’ve gotten variations on this question from several friends through the years, and have seen a huge increase in the number of questions about soil for backyard gardening on local Facebook groups in the past few weeks. My guess is that people are reluctant to plant directly into the ground because of three major reasons: 1). weed pressure, 2). accessibility, and 3). they’ve tried digging a few holes and the soil is so compacted they gave up.
If you don’t have accessibility concerns and you can stand to dig a garden plot a few inches deep, keep it relatively weed free by pulling weeds regularly, and plant directly into the soil, that may be your best bet. Containers and raised beds have benefits, but they also have some downfalls. For one, they tend to dry out much more quickly. Drainage is necessary, but containers can dry out so fast plants can wilt between waterings. They’re also more exposed to the elements, so the soil and roots can get much hotter in the summer (and colder in the winter) than they do in the ground. Consider painting pots white or a pale color to reflect more sunlight so they stay a little cooler.
Whether you’re planting in the ground or in containers, mulching on top with any fibrous organic material (straw, leaves, woodchips) will help in multiple ways. Three to four inches of mulch helps suppress weed germination and growth, holds moisture in the soil, keeps the rooting area cooler in summer (and warmer in winter), prevents water and wind erosion, and prevents surface crusting (which inhibits water penetration). Over time, mulching also provides much-needed nutrients that feed beneficial soil organisms, increases organic matter and improves soil texture, and eventually enhances the soil’s ability to store nutrients for plant root uptake. Of course, if you’re direct-seeding your garden beds or containers, adding a thick layer of mulch too soon can inhibit seed sprouting. You can either transplant seedlings and add mulch around them or scoot the mulch away in the spots where you’re planting seeds.
But back to the question of planting mix. To a large extent, it really depends on two things: what are you trying to grow and what kind of existing soil you have at home. Warning: If your yard is full of weeds, your soil is likely full of weed seeds too. And the soil under the mulch will keep that weed seed bank for many years to come.
I asked my farming friend, Dr. Willy Carleton, who grows chiles, sweet potatoes, and all sorts of other vegetables outside of Española, what advice he’d like to share. Willy stressed that soil texture is extremely important. Think “fluffy with good drainage.” If you shovel soil from your yard into containers or beds, the result may be anything but fluffy with good drainage. If your yard soil is sandier, the plants theoretically would stand a better chance because of better drainage.
I also reached out to longtime gardener and certified desert landscaper, Tsu Dho Nihm, for sharable tips: “Do not use cardboard as a weed blocker under a raised bed” because it restricts oxygen flow, which is harmful to beneficial organisms like earthworms. And “don’t put rocks in the bottom [of containers]. They don’t help with drainage. Don't worry about amending and fertilizing until you have tried growing some things and see how they do. Don't reach for a ‘fix’ until you are sure what the problem is. If you have a problem, check your watering practices first.” Tsu Dho Nihm’s blog Lazy Gardening offers great options for no-tool, cheap raised bed plans and frost shelters (which can double as shade shelters), among other local gardening topics. For more on the cardboard comment, visit The Garden Professor's. For more on why to skip putting rocks in the bottoms of pots, visit Desert Blooms and search “drainage” for my 2018 blog post about fungus gnats.
According to NMSU Extension Circular 457: Home Vegetable Gardening in New Mexico, one of the easiest ways to improve soils is to add organic matter, such as livestock manure. See Circular 457 for more info on how much organic matter to apply and when.
Other helpful NMSU Extension publications include Circular 687: Managing Organic Matter in Farm and Garden Soils, and Circular 694B: Soil Health—Importance, Assessment, and Management.
“Seed to Supper: A beginner’s guide to low-cost vegetable gardening” is an amazing new resource. First developed by the Oregon State University Extension Service in collaboration with the Oregon Food Bank, these materials were adapted by NMSU’s Cooperative Extension Service for gardening in New Mexico, and have just been released as a free, self-paced, online course through NMSU’s ICAN (Ideas for Cooking & Nutrition) program. Join me as I explore this resource and teaching format (which includes how-to videos) by visiting Seed to Supper. Here’s a sneak peek from a section on container gardening: “You can also make your own potting soil from equal parts sand or perlite, loamy garden soil, and peat moss or coconut pith. Depending on your circumstances, this may be cheaper for you.”
Whatever you decide to use for your gardening needs, take lots of pictures and let me know how it grows. I’d love to survey you all at the end of the season to see what worked and what didn’t.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!