Containers let you grow food where there is no ground to dig: on a balcony, a patio, a driveway, or a sunny doorstep. Most vegetables and herbs grow well in them. What changes is how little room the roots have. In a bed, roots can reach for water and nutrients well beyond the plant; in a pot, they have only what you give them.
The short answer
- Use a bigger pot than you think. Leafy greens manage in a gallon; full-size tomatoes want 5 gallons at least, and vining types 10 or more.
- Fill it with potting mix, not garden soil or topsoil. Soil packs down and drains badly in a pot.
- Make sure there are drainage holes, and skip the gravel layer. Gravel at the bottom keeps the mix wetter, not drier.
- Water more often than a garden bed, often daily in hot weather, until water runs out of the bottom.
- Feed little and often. Frequent watering washes nutrients out, so they need regular replacing.
How big a pot each crop needs
Pot size is the decision that matters most. A small pot dries out quickly and leaves roots little room, and the plant stays small and stressed. A larger pot holds more water, so it needs watering less often. Extension guides give slightly different minimums; these ranges cover them.
| Crop | Minimum container |
|---|---|
| Leaf lettuce, spinach, and other greens; radishes | ½ to 1 gallon per plant or small group, 6 to 8 inches deep |
| Small herbs such as basil, chives, and thyme | 1 to 5 gallons, depending on the herb |
| Large herbs such as rosemary and sage | 5 gallons or more |
| Peppers and eggplant | 2 to 5 gallons |
| Cherry and compact (determinate or "patio") tomatoes | 2 to 5 gallons |
| Standard tomatoes | 5 gallons |
| Vining (indeterminate) tomatoes | 10 gallons or more |
Anything that holds mix and drains can be a container: a plastic pot, a 5-gallon bucket with holes drilled in the bottom, a fabric grow bag, or a wooden box. A 5-gallon pot holds about two-thirds of a cubic foot, so a 2-cubic-foot bag of potting mix fills about three of them.
Use potting mix, not garden soil
Garden soil and bagged topsoil are too heavy for containers. In a pot they pack down, drain slowly, and leave roots short of air. Use a soilless potting mix, which is light and stays open after repeated watering.
Read the bag. "Potting mix" made for containers is not the same as "garden soil" or "raised bed soil" made to dig into the ground. Moving a houseplant up a size? See how to repot a houseplant.
Drainage holes, and why gravel backfires
Every container needs holes in the bottom. A pot without them fills with water like a bucket and drowns the roots. If a decorative pot has none, drill some, or grow the plant in a plain pot that sits inside it.
Do not add a layer of gravel, pebbles, or pot shards at the bottom. It feels like it should help drainage, but it does the opposite. Water does not move from a fine material like potting mix into a coarse one like gravel until the mix just above is saturated. The gravel raises the soggy zone, called a perched water table, higher into the root zone, and takes up space the roots could have used. Washington State University Extension calls it a myth that refuses to die. The vegetable garden guide explains the physics. To keep a hole from losing mix, cover it with a piece of screen or a coffee filter instead.
Watering: more often than you think
Containers dry out far faster than garden beds, because the root zone is so small. In hot, dry weather, a pot in full sun often needs water every day, and sometimes twice.
- Check before you water. Push a finger into the mix; if the top inch or so is dry, water. A pot that feels light when you tip it is dry too.
- Water until it drains. Keep going until water runs out of the bottom, so the whole root ball is wet, not just the surface.
- Empty saucers after watering, so the pot doesn't sit in water.
- A mix that has dried out completely can shed water down the sides of the pot. If water runs straight through, water again slowly, or stand the pot in a tray of water until the mix soaks it up.
The watering guide explains how to judge the root zone by feel and weight.
Feeding: little and often
Every time water drains out of a pot, it carries nutrients with it. Even a potting mix that starts with fertilizer in it will run short over a season of daily watering, so nutrients need replacing regularly.
- Slow-release fertilizer, coated granules mixed into the potting mix at planting, releases small amounts each time you water.
- Water-soluble fertilizer, mixed into the watering can, works quickly; for most containers, about every two weeks is enough.
Use the rate on the label. In a small volume of mix, too much fertilizer builds up as salts that burn roots and leaf edges, the same problem the yellow leaves guide describes for houseplants.
Crops and varieties that suit pots
Almost any vegetable can grow in a container big enough for it, but some suit pots far better than others.
- Easiest: leaf lettuce, spinach and other greens, radishes, green onions, and herbs such as basil, parsley, and chives.
- Good in larger pots: peppers, eggplant, bush beans, and tomatoes, especially determinate, "patio," or cherry varieties bred to stay compact.
- Hard work in pots: sprawling crops such as winter squash, pumpkins, and melons, and anything that needs a long root run.
Look for variety names or descriptions that say bush, compact, dwarf, or container.
Sun matters as much as size. Tomatoes, peppers, eggplant, and squash need six to eight hours of direct sun a day. Lettuce, spinach, and other cool-season greens manage with three to five, which makes them the best choice for a balcony that gets only morning or afternoon sun.
At the end of the season
Empty annual vegetables out of their pots in fall and add the old mix to the compost pile, or to a garden bed. Pots of perennial herbs or shrubs left outside face a hazard in-ground plants don't: their roots are above ground, with no soil around them to hold heat. The frost protection guide explains how to shelter them.
Sources and further reading
- University of Maryland Extension: Growing vegetables in containers and salad tables — container sizes, potting mix, and drainage.
- University of Illinois Extension: Growing vegetables in containers — sizes and suitable crops.
- Texas A&M AgriLife Extension: Vegetable gardening in containers (E-545) — container sizes by crop.
- Colorado State University Extension: Vegetable gardening in containers (CMG GardenNotes #724).
- Washington State University Extension: Container drainage (Linda Chalker-Scott) — why a gravel layer raises the perched water table.
- University of Minnesota Extension: Fertilizing and watering container plants — daily watering in hot weather and nutrient leaching.
- University of Illinois Extension: Container gardens — fertilizing — slow-release and soluble fertilizers.
- University of Maryland Extension: Maintaining container-grown vegetables.
- NC State Extension Gardener Handbook: Plants grown in containers — sun by crop type and herb container sizes.