Want to grow vegetables but have limited outdoor space or no “dirt” of your own? Like the ease of growing in pots versus in the ground? Sounds like container gardening is made for you. Here are some helpful tips for successful gardening in pots.
What to Plant
Peppers, squash, greens, potatoes, basil are among the many plants that grow well in containers – check this Planttalk Colorado publication for details and inspiration. When purchasing plants or seeds, look for cultivars described as compact, dwarf, patio or bush. Determinate tomato varieties work well but I also have great success with ‘Sun Gold’, a sweet, prolific indeterminate cherry tomato. (Determinate varieties tend to ripen all at once while and grow on bushier plants, while indeterminate ripen over a longer period and tend to be larger plants.)
Where and When to Plant
Generally, vegetables and herbs need 6-8 hours of sun a day. Placing your container on a strong dolly with wheels allows you to move the plant to find the ideal space. A dolly also helps you quickly shelter your plants from Colorado’s wicked summer hailstorms.
Warm season vegetables such as tomatoes should be planted when evening low temperatures are consistently above 55 degrees. Don’t rush things – in Denver, this generally means late May, even though Mother’s Day weekend is touted as the kickoff to the gardening season.
What Container to Use
The larger the plant, the larger the root system. Salad greens successfully grow in pots that are 6-12” deep and at least 18” wide, while a tomato needs at least a depth and width of 14-16″ or more. Larger pots are less prone to drying out rapidly and because they hold more growing medium, the plant receives more nutrients and has plenty of room for root development. Generously sized, heavy containers anchor large plants in the wind and will help avoid tipping and broken branches.
Plastic, glazed or unglazed clay pots or wood whiskey barrels are popular choices. Unglazed clay pots can require more frequent watering, especially in the hottest part of the season. No matter what your container is made of, it must have good drainage holes.
Don’t forget to add support for vining or large plants – stake, cage or trellis your plant just as you would if it was in the ground. These plant aides are easiest to add before the plant needs it. Wrestling a metal cage over a sprawling plant is not fun and may not be successful. I’ve tried.
Soil and Fertilizer
Use potting media specifically for containers and/or vegetables, often labeled soilless. “Soilless” potting soil sounds like an oxymoron, doesn’t it? Just like traditional potting soils, it can contain peat moss for nutrients, vermiculite for water retention and perlite to aide in air movement around the roots. The mixture will weigh less and is good to use in heavy containers.
Container veggies grow vigorously and therefore require lots of nutrients. Some mixtures contain time release fertilizers, which help plants get off to a good start, but will not feed plants for the entire season. Excellent information on using soluble and time-release supplements in our region can be found here.
Penn State Extension noted that time release fertilizers release nutrients faster in warm weather; a pellet fertilizer labeled to last 4-5 months will only last 2 months if the temperatures are above 85 degrees.
According to Colorado State University, “Organic fertilizers such as fish emulsion or blood meal can also be used if desired but may be available too slowly for actively growing plants or may develop sour aromas that attract pets and pests.”
I’ve always added gravel or broken clay shards to the bottom of pots for drainage. Turns out, it’s not necessary or even advisable. Studies by Washington State University and others found that a layer of inorganic material drives excess moisture up to the roots rather than helping with drainage. Excess moisture suffocates roots and reduces oxygen flow. So, this year, I’m simply covering the drainage holes with pieces of metal screen to keep soil from leeching out. Paper coffee filters can do the trick too.
When to Water
There is no one-size-fits-all answer to this often-asked question. A best practice is to check plants daily, ideally in the morning. Poke your finger into the soil, if it is starting to dry out at your first knuckle, water at the soil line till water flows out the bottom of the pot. Consider factors such as temperature, wind, reflective heat from surrounding hard surfaces, and as mentioned earlier, the type of container used. In the heat of the summer, you will likely water every day, possibly twice.
Do not allow vegetables to dry out completely – they may not forgive you! Results of underwatering can include deformed fruit, poor growth, disease or even loss of the plant.
So there you have it, a round up of solid research-based advice for container gardening. Growing edible plants in pots is rewarding and can yield excellent results. It’s a reliable method for experienced and beginning gardeners alike. If you’ve never given it a try, its a fun summer activity which can provide plenty of healthy, tasty rewards.
Written by Linda McDonnell, Denver County Master Gardener