Container Gardening 101: What You Need to Grow

August 7, 2021


The only difference between a gardening guru and a newbie gardener is the number of plants they’ve killed. This column is for beginners interested in growing something in a container for their patio or doorstep but who don’t quite know where to start. Or maybe they’ve tried a few times half-heartedly, and it didn’t end well.

Container gardening 101 includes the container type and size, drainage, soil selection, recommended plants, more drainage, placement, and irrigation.

What size of container is best? Generally, use large pots for large plants or combinations of small plants, and use smaller pots for individual small plants. Note that the smaller the pot, the more quickly you can expect it to dry out. And avoid using a large container with a single, tiny plant because that extra soil can be problematic—either it draws moisture away from the roots, drying the plant too quickly, or it holds moisture too long and can cause root decay.

The first thing to look for when shopping for pots is a decent drainage hole in the bottom or several smaller drainage holes. I do not recommend pots with attached saucers for beginners because it’s too hard to tell if water is draining well. Sometimes pots are sold without any holes at all. If so, you’ll need to drill your own. Five or six holes about 1/4 inch each is a good start. For bigger pots, more holes may be necessary.

Image of person drilling holes on a planter
Adequate drainage in a growing container is a much bigger deal than many new gardeners realize. Photo credit Marisa Thompson

Terracotta (unglazed clay) pots usually come with a single hole in the bottom, and that’s good because they’re trickier to drill. Let’s say you’ve selected a terracotta pot that’s 16 inches wide at the top—the size of a large pizza. Did you check the drainage situation? Good. Now let’s fill it with soil.

The most important thing about container soil is—you guessed it!—good drainage. As a beginner, resist the urge to pick a “moisture-retaining” type of soil. A basic potting soil mix will work great. Unfortunately, digging up soil from your own yard (or someone else’s) to use in containers is not a good idea. If it worked well, please believe that I’d be the first to encourage it. I’ve tried several times since I moved to New Mexico in 2004, in several different zip codes and for several reasons (I was trying to save money, I was in a hurry), but it was never successful. At least once I convinced myself that the sandy soil in my yard would be great in terms of drainage. As explained in a University of Illinois Extension resource on container gardening, “When choosing what to use to fill containers, never use garden soil by itself no matter how good it looks or how well things grow in it out in the garden. When put into a container both drainage and aeration are severely impeded, and the results are that plants grow poorly or not at all.” See Univ. of Illinois.

We’re finally at the point of picking plants for this 16-inch container. I like placing several smaller plants in a container together because it’s less noticeable if one or two die. For me, herbs are some of the easiest plants to grow, so let’s pick five or six if they’re available in 4-inch pots or smaller, or three or four if they’re in quart-sized containers. Basil, mint, culinary sage, oregano, rosemary, chives, and parsley are all great bets.

Even though it’s August, now is a great time to start a little herb garden. Many herbs are remarkably cold-hardy, which means they’ll either keep growing into the winter or they pop back up from the soil in the spring.

Image of a green spearmint plant
The spearmint in this photo is completely filling the purple pot it’s growing in. Photo credit Marisa Thompson

Using gravel at the bottom of a container to help with drainage is a myth. For more info, visit my Desert Blooms blog and search for the 2018 column titled, “Draining or Retaining? Fungus Gnats and Other Side Effects of Poor Drainage.” If your container is very big, it could be costly to fill it with packaged soil. We already learned that yard soil isn’t the answer, but you can use other materials to take up space so you use less store-bought soil. Packing peanuts work well. So do crumpled empty milk jugs. And I’ve also used another smaller pot placed upside-down inside the larger pot to take up extra space.

Back to our herbs. Moisten the soil in your pot before adding the plants, and pack it down a bit too. Don’t fill the pot all the way up to the edge with soil because you’ll want at least a 2-inch lip so you can water from the top without splashing soil out everywhere and making a mess. Plus, you’ll be digging little holes for the plants. Settle each herblet deep enough in the container so that the roots are barely covered by potting soil.

OK, we’re almost done. But don’t just set it and forget it. Pick a place outdoors that gets a few hours of direct sun (either morning or evening exposure) or several hours of dappled light (like under a tree). Water it well and check on it every day for the first week or so. As Bernalillo County Extension Agent and County Program Director John Garlisch says, “The best soil moisture meter is your finger.” Test the soil at least a few inches down and apply water when it feels dry. If it’s drying out very quickly between irrigations, try a cooler location without as much sun. In the hottest months, containers in my yard get watered deeply every three days or so, and they’re positioned strategically so that they get shade for most of the afternoon. During winter, I water them about once every four to six weeks. For photos of my patio plants and container gardens all over Albuquerque, visit the blog at the URL mentioned above.

And for more tips and ideas (and confessions), find a recording link to the recent Ready, Set, GROW! webinar titled Container Gardening. Ready, Set, GROW! is an ongoing gardening webinar series hosted by the NMSU Cooperative Extension Service. Upcoming topics include fall veggie garden planning, cover crops and fruits for the home gardener, healthy soils, and composting.


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: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!