Container Vegetable Gardening 101
By Chris Colby
Freshly harvested garden vegetables — you can’t beat ’em. You might think you need a good garden spot to grow them, but you don’t; you can grow delicious vegetables in containers almost anywhere. For people who live in the city, or even in an apartment with a deck, a container garden can supply fresh vegetables during gardening season. And even if you do have that garden plot, you can expand the variety of plants you are growing by establishing an additional container garden.
I have a full-size, in-ground garden, but it gets a bit of shade in the afternoon. The sunniest spot on my property is my driveway, so I’ve used container gardening to grow a lot of veggies that do best in full sun. These include tomatoes, peppers, corn, pole beans, squash, hops, and all sorts of herbs — basil, coriander, mint, etc.
Pick perfect containers
When planning an in-ground garden, you first decide on the layout. With a container garden, you can worry about that later, since the containers are movable. As the growing season progresses, you can arrange them to account for changes in the patterns of sun and shade, or if one plant begins to shade another.
Your first step when planting a container garden is to decide what you’re going to grow, and then select appropriately sized containers. With the right-sized container, you can grow almost any common garden vegetable. Root vegetables or tubers can be more difficult, as they require containers large enough to hold both the vegetable and the roots. Likewise, large cucurbits like pumpkins and watermelons produce vines that root at every node, and growing full-sized pumpkins or melons in containers is difficult. However, the vast majority of common garden veggies are easy to grow and will turn out great.
Choose the right container
From the standpoint of plant health, the best solution is to select a container large enough so the roots just barely reach the sides and bottom when the plant reaches maturity. However, for most vegetables, this would require large containers and limit the amount of plants you could grow in a given area. In practice, you can grow vegetables in containers that restrict root growth somewhat, as long as you pay attention to watering and fertilization.
For upright plants or trellised plants, you can get some idea of how much space their roots require by reading seed catalogs and noting the recommended row spacing for the plants. Take the distance between seeds or transplants in a row and divide by two to yield the diameter of a container that should be a good compromise between crowding the roots and taking up too much space — and potting mix, soil, fertilizer, compost, etc. — in your container garden.
The depth of the container should be roughly equal to the diameter. For example, many garden guides suggest spacing tomatoes 4 feet apart in a row. This would suggest that a 2-foot-diameter planter would be adequate. I have grown tomatoes multiple times in 22-inch-diameter pots (just shy of 2 feet), and the plants have grown large and healthy. For sprawling plants, you may need to experiment to find an appropriately sized container. In addition, plants that produce large or a large number of fruits will need more space for roots than, say, herbs, which can grow in comparatively small pots. If you have the space — and the budget — for containers, it’s better to err on the side of larger containers.
In past years, I planted my veggies in small containers, then “up potted” the best growing individuals into larger containers as they grew. This requires the purchase of more planters, a greater expenditure of time, and entails the possibility of damaging the plants when you move them to a larger pot. These days, I plant everything in the container it will grow in. This also allows me to move the containers around to experiment with my container garden layout before the plants get too big.
Nurseries and big box stores sell all sorts of planters — from clay, to plastic, to wood. Used wine barrels are also frequently sold as decorative planters. The plastic planters are by far the cheapest, but be aware that the plastic will become brittle and break down after a few years in the sun. Once they crack, you can usually get one more year of service out of them by sealing the crack with duct tape.
If the containers don’t need to look nice, you can use 55-gallon drums, old buckets, or other household containers as planters. Just be sure the container did not previously contain anything toxic, or that the container itself is not made of or has not been treated with anything toxic. Also, you will need to drill drainage holes in the bottom of any potential planter.
Some plants grow best on a trellis. If you plan to trellis any of your vegetable plants, install the trellis at the same time you plant. Tomatoes and peppers can be trained to a single stake inserted into the container, or a cage can be installed around them. Many veggies — like pole beans and cucumbers — will grow onto a simple trellis placed next to or over the containers. If you guide the first vines onto the trellis and tie them in place, you’ll be able to keep their growth orderly.
Drainage is key
If you follow the sizing advice above, the roots of your plants are going to be constrained. They will grow to the edge and bottom of the container, and then bunch up. The matrix they grow in needs the best drainage possible, which will allow you to water and “feed” the plant efficiently.
Fill each container with good-quality potting mix or another soil-like medium with excellent drainage. Actual soil — even rich garden soil — is usually not a good choice unless your containers are large and only minimally restrict the root systems. Also, soil is heavier than potting mix and makes a container more difficult to move.
Fill the containers to the top with potting mix, and then add a little bit more so there is a slight hill on top. Take a board or ruler to push the top layer off, leaving a level surface. This will give the plant roots as much volume to grow into as possible, given the container. Shake the container to get the potting mix to settle, but don’t forcibly compact it. The first few times you water, the potting mix may compact a bit. Also, as the season progresses, a small amount of potting mix will wash out of the container through the drain holes. Don’t add more potting mix; the level of the “soil” slightly below the lip of the container will help you when watering.
Do not line the bottom of the pot with gravel or small rocks. Many people believe this helps with drainage when, in fact, it impedes it. An uninterrupted volume of potting mix is like a sponge. If you set a sponge on level soil, the water from it would gradually be transferred to the ground. However, if you placed a layer of gravel between the sponge and the ground, the water would cling to the sponge.
Compost is good food for plants, but too much in a container slows drainage. If you use compost in your containers, make compost tea and use it to “feed” the plants.
Most commercial potting mix these days contains time-release fertilizer. You are better off using a mix that does not contain such fertilizer. Your goal in growing a container vegetable is to supply it with enough nutrients so the plant is healthy, but not cause it to grow excessively vigorously, and thus require an even larger root system to support. If you do get potting mix with fertilizer, run several gallons of water through the mix to wash away the initial load of highly soluble material. Collect this runoff to water your lawn or garden.
Soak the mix
When it’s time to water, soak the container so every bit of the potting mix is wet. You’ll know this has occurred when water begins seeping from the drainage holes. Immediately after watering, every root hair in the pot should have access to water. Don’t water again until the top 1/2 to 1 inch of potting mix has dried out. Potting soil changes from black to dull gray when it dries, so this is easy to spot. And, of course, keep an eye on the plants for signs of water stress, including leaf rolling and wilting. When you water again, completely soak the container.
If you don’t soak the container each time you water, the bottom of the potting mix can dry out and stress the roots, further limiting their ability to absorb water and nutrients. Your containers will receive sporadic and light rains occasionally, but even if the plants look healthy during these times, you may need to water them deeply every once in awhile to ensure all the potting mix is damp.
Potting mix has excellent drainage qualities — no need to worry about “overwatering” if you follow a pattern of soaking the container, then letting it almost dry out.
Growing veggies in containers cramps the root system, and the volume of water and nutrients they are absorbing is reduced. Compensate for this by fertilizing the plants. The best way is to regularly add diluted mixtures of water-soluble plant fertilizer. Use “regular” liquid or granular plant fertilizer, or organic fertilizers like compost tea, seaweed extract or fish hydrolysate.
Mix up some plant fertilizer to a fraction of the strength recommended by the manufacturer, but use it more frequently than recommended. In other words, spread the addition of the fertilizer out over time. For example, if the mixing instructions are to use 1 cup of fertilizer once a month, try adding 1/4 cup every week, or 1/2 cup every two weeks. You’ll end up feeding the plant the same amount, just not in big, infrequent doses. Give the plant just as much as it needs as it goes along. Make notes to refer back to in future years, and you’ll find what works best in your situation.
Make the diluted fertilizer solution and soak the container. You can coordinate “feeding” with your watering schedule and take care of both at the same time. Ideally, you’ll want every bit of the potting mix to be wet with the solution, so all the roots can take in nutrients evenly. It helps to have a large watering can and mix up the fertilizer solution in portions, or use big buckets in which to mix the diluted fertilizer solution.
If you mix up a concentrated blend of fertilizer and add it only on top, the nutrients will reside in the top layers of the container while the bottom roots are in a low nutrient environment. If the solution is too concentrated, it can even “burn” upper roots.
Do not over-fertilize. You’re already cramping the roots, so don’t compound the problem by adding too much nitrogen and growing a monster plant. Add just enough fertilizer to keep the plant healthy; an easy way to tell a plant’s health is by leaf color.
If you overfeed a plant, or add an overly concentrated solution, water again until that liquid exits the pot. This flushes most of the unused fertilizer (if any) from the pot. You can wait until the next day to do this, unless you’ve really overdone it.
If you fertilize on a schedule, examine plants before each fertilizer addition. If the leaves are healthy and green, limit the fertilizer you give the plant or skip the “feeding.” You don’t gain anything by stimulating the plants to grow excessively.
If the aboveground growth of your plant becomes too much for the root system to handle, it helps to prune the plant. If you grow tomatoes, you can remove the suckers at a minimum. If the plant grows too large, you can also prune secondary stems.
Vining plants, including melons, can be pruned down to only the main vine, if needed. Remove the smallest secondary or tertiary vines if the plant wilts every day. If it doesn’t perk up in the few days after pruning, prune the next largest set of vines.
For plants that grow out of a container and onto a trellis, pruning excessive vine growth ensures that all the leaves get sun.
Tie it all together
The smaller the containers, relative to what’s best for the plant, the more work it will be to keep it watered and fed properly. Save a lot of headaches by starting with the biggest containers you have room for and filling them with straight potting mix.
Properly tended, a container garden can yield a bounty of vegetables comparable to what an in-ground garden with the same number of plants would deliver.
There’s more to know.Avoid These Container Gardening Mistakes for greater success.
Chris Colby is an avid gardener who lives in Bastrop, Texas, with his wife and cats. His academic background is in biology, but his main interest is in brewing beer.
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