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Big Ideas for Small Spaces: Tips for Successful Container Vegetables

Peppers and tomatoes growing in containers. Photo: Julie Weisenhorn
Don't have space for a garden? You can still grow vegetables and herbs in containers! Here, we give several key tips for successfully growing container vegetables this season:

1) Peruse seed catalogs and garden centers to find varieties well-suited for containers

Some varieties do better in containers than others. In general, a good container variety will have a bush-like shape rather than a climbing habit, and will remain fairly compact. 

For tomatoes, choose "determinate" varieties rather than "indeterminate". Determinate varieties will keep a bush-like shape, and will ripen all at once, whereas indeterminate varieties will keep growing upwards and require additional staking or trellising

Some seed catalogs indicate which varieties do well in containers, and others are less specific. Look for terms like "compact", "determinate", or "does well in containers." University of Illinois also has a list of varieties well suited to containers.

Some seed catalogs indicate which varieties are well suited to containers; online catalogs may have filters for this. Image: Johnny's online catalog.

If you're buying transplants rather than starting your own seeds, most garden store employees will be able to recommend a good variety for containers.

2) Choose your potting soil wisely

Healthy plants start with healthy soil. Soil straight from your yard or garden beds will not perform well in a pot. A pot is a unique environment; soil in containers needs to be able to both drain well and hold on to some moisture. Remember that your pots need to have holes in the bottom for drainage. Without holes, you risk over watering and creating an anaerobic (oxygen deprived) soil environment. 

When selecting potting soil, you have a couple of options:

The easiest option by far, but perhaps the most expensive, is to purchase potting mix from your local garden or hardware store. These mixes often do not contain any soil at all, and are rather mixes of materials like bark, vermiculite, peat, coconut coir, sand, and other materials. Different mixes are better suited to different plants. 

For example, succulents and herbs tend to do better in mixes that drain water more readily (usually due to more sand and perlite). Annual vegetables do well with a little more moisture retention, so these soils may contain more coir, bark, or peat. Read the description on the bag to choose the mix that will work best for your needs.

You can also take soil from your garden, but you'll need to amend it. Soil from the garden tends to be heavier and will not drain as readily. Adding materials like vermiculite can help to aerate the soil and promote better drainage. Unfortunately, every soil is a bit different, so there's not a universal recipe for this. One option could be to use 1/3 to 1/2 soil from your garden and 1/2 to 2/3 potting mix. One disadvantage of soil from the garden is that it's more likely to contain insects, weed seeds, and diseases.

Over the years, the organic materials in your potting mix will break down, and the plants in your pots will absorb the nutrients in the mix. After a year or two, you'll need to use new potting mix, or amend it with more organic material and nutrients.

3) Choose a container large enough for the full-sized plants

Some vegetable plants grow to be quite large. As they grow, they need nutrients, water, and sufficient space for their roots to expand in the soil or potting media. Therefore, be sure to use pots that are big enough for the size your plants will grow to.

A 3-gallon pot containing a medley of herbs. 
Photo: Julie Weisenhorn.
Some signs that your plant is too big for its pot include:
  • soil drying out frequently 
  • stunted growth 
  • lack of productivity
  • discolored leaves (lack of nutrient uptake)
While a single basil plant may survive all season in a one-gallon pot, things like cucumbers, tomatoes, eggplants, and peppers will do much better in larger containers. Here are some examples of minimum container sizes for popular vegetables:

1-gallon containers: basil, 2-3 peas, spinach lettuce, 1 head of cabbage

2-gallon containers: beets, short carrots, "patio" type hot peppers, cucumbers, "patio" sized cherry tomatoes

3-5 gallon containers: Standard sized tomatoes, bell peppers, eggplant, potatoes, longer carrots, miniature herb gardens

Experts do not always agree about the minimum container sizes for each vegetable type, so it is safer to be conservative and reach for a larger size when in doubt. 

For instance: This article from University of Illinois Extension recommends planting 2-3 green bean seeds in a 1-gallon container, while this article from Texas A&M University recommends a minimum of 2-gallons for green beans.

If the container you originally planted in becomes too small, and your plant starts showing signs of stress like discolored leaves and stunted growth, it is alright to transplant it to a larger container during the season. 

4) Make sure that the pot has drainage holes

It is easy to make the mistake of potting up plants in a pot that lacks drainage holes in the bottom. Without drainage, the water has nowhere to go, and the soil will become saturated over time.

Saturated soil can kill or drastically stress plants, because it impedes the roots from taking up the nutrients they need from the soil. Find a container with holes in the bottom, or drill your own holes. 

5) Place the containers in a spot with direct sun for most of the day

While semi-shaded areas can be suitable for herbs and ornamental plants, most vegetable plants require more sun. Find a spot that has full, direct sunlight for at least eight hours or more.

Container peppers and tomatoes in direct sunlight. 
Photo: Julie Weisenhorn
Why full sun? For many types of "vegetables" we grow, the part we eat is actually the fruiting body of the plant. For instance, when we eat peppers, cucumbers, eggplants, and tomatoes we are technically eating the fruits of the plants.

It takes a lot of sunlight, nutrients, and photosynthesis for vegetable plants to produce and ripen these fruits.

If the container is placed in an area that is shaded for half the day or more, the plant will likely have difficulty ripening fruit.

Example: A patio on the south-facing side of a building has direct sunlight for a much longer portion of the day than a patio on the north, west, or east-facing sides of a building, assuming there are no trees shading it.

If placing your containers on the south side of your building is not an option, or you have a tree that shades your patio for more than half of the day, then it will be best to choose a type of vegetable that does not produce fruits, like lettuce, spinach, peas, or carrots. However, never choose an area that is totally shaded.

6) Water regularly, but not too much

Check your containers daily, and water only if needed. To determine if you need to water, stick your finger in the potting media about an inch deep. If the potting mix feels moist or wet, you do not need to water yet. If it feels dry at an inch deep, it is time to water.

Apply water just until the water accumulates above the soil, and then let it drain down. If it takes a very long time to drain down, the pot may be over-watered. If the pot is extremely dry, i.e. if the plants have wilted, or if it feels oddly light when you pick it up, then more water will be needed.

Very small plants do not take up water at the same rate as larger plants, so newly planted seedlings may not need to be watered as frequently.

Why is over-watering a bad thing? To a beginning gardener, it may seem that more water is better, but that is not the case. Most plants that we grow, including vegetable plants, can die or become very badly injured when sitting in standing water.

As described above, too much standing water makes it difficult for the roots to take up the nutrients they need. In some cases, it can cause the roots to rot altogether. Standing water can also lead to plant diseases like powdery mildew and botrytis.

We hope that you have found these tips to be helpful, and you feel prepared to go out and start a container garden this spring! Happy gardening.

Authors: Annie Klodd and Natalie Hoidal, UMN Extension Educators for Fruit and Vegetable Production
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