Growing vegetables in containers: a South African quick-start guide

Every spring someone walks into the nursery with a punnet of tomato seedlings and a pot the size of a coffee mug, full of hope. We love the hope. We just want the tomatoes to happen too, and after years of growing our own on a Centurion stoep that bakes from November to February, we have learned exactly where container vegetables go right and where they quietly fail.

This is the short version of everything we tell people over the counter. It is written for South African conditions, which means Highveld frost in June and July, afternoon thunderstorms in summer, water restrictions when the dams drop, and a Cape climate that runs almost backwards to ours. If you want the full, long treatment read our growing food in pots guide afterwards. This one is for getting started this weekend.

Plant by our seasons, not by a Northern Hemisphere packet

Most seed packets sold here still carry planting months written for England or America, and following them is the fastest route to disappointment. In Gauteng, Mpumalanga and the Free State the warm-season crops go in from mid September once the last frost has passed, and that means tomatoes, peppers, brinjals, bush beans, baby marrows and cucumbers. They run until the first frosts of May or June. The RHS guide to growing tomatoes makes the point that matters everywhere: plant them out only once temperatures are reliably above 16 degrees, and give them the warmest, sunniest, most sheltered spot you have.

The cool season, from late March through to August, belongs to lettuce, spinach, Swiss chard, peas, beetroot, radishes, spring onions and coriander, which bolts to seed the moment it feels a hot day. In Cape Town and along the Garden Route the winter rains do most of the watering for these crops, and summer is the hard season, so many Cape gardeners grow their leafy greens through winter and rest the pots in January. Coastal KwaZulu-Natal barely has a cold season, so tomatoes can go in almost any month and the challenge is humidity, not frost. If you are unsure what to plant right now, the Garden Planner is built around these regional windows.

Count your sun hours honestly

Before buying anything, stand in the spot at nine, at noon and at three on a clear day and note whether it is in direct sun. Fruiting crops, and that means tomatoes, peppers, brinjals, beans and squash, need six or more hours of direct sun to set and ripen fruit. Illinois Extension's guidance on growing vegetables in containers puts full sun at a minimum of six hours, and we would say a Highveld tomato is happier with eight. Leafy greens and most herbs are content with four hours, and in the height of January they actually prefer some afternoon shade.

The nice thing about pots is that you can move the sun to the plant. A lettuce trough that sits on the east side of the house in summer, catching morning sun and escaping the afternoon, can be dragged into the open for winter. That flexibility is the single biggest advantage containers have over a vegetable bed.

Depth per crop, in centimetres

This is the number people get wrong most often. Leafy greens and herbs, so lettuce, rocket, spinach, basil, parsley and coriander, are shallow rooted and manage well in 20 cm of soil. Root vegetables need room to go down: carrots, beetroot, turnips and spring onions want 30 cm, and the RHS notes in its carrot growing guide that anything stony or compacted gives you forked, wonky roots, which is exactly what a shallow pot does too. Tomatoes, peppers, brinjals and bush beans want 40 cm or more, and a full-size tomato honestly does better in 50 cm.

Depth is also about water. A 20 cm pot on a north-facing wall in December can dry to dust between breakfast and supper. A 40 cm pot holds enough soil to carry the plant through the afternoon. This is why we steer vegetable growers toward troughs rather than a clutter of small pots. Something like our Curo Trough gives you a metre of consistent depth, room for three tomatoes with basil between, or a full salad bed, and the mass of concrete keeps the root zone cooler than thin plastic ever will.

Soil, and why the garden bed stays in the garden

Garden soil compacts in a pot, drains badly, and brings every weed seed and cutworm with it. Use a potting soil made for containers. Our Bark Outdoor Potting Soil is what we plant our own vegetables in, and for hungry crops like tomatoes we mix a third of Bark Compost into it before planting so there is something for the roots to find in the first month. Fill the pot to about 5 cm below the rim so you can water without it running off the top.

In anything deeper than about 60 cm a layer of Pot Filler in the base is worth it. It saves soil, improves drainage and stops the bottom of the pot turning into a sour, waterlogged layer that roots avoid anyway. Never let a vegetable pot sit in a full drip tray for more than an hour; empty it or lift the pot onto concrete pot feet so the hole drains freely.

Watering through Highveld heat and Cape summers

Water early, before eight if you can. Morning watering soaks in before the heat, gives leaves time to dry so fungal problems stay away, and means the plant faces the afternoon with a full tank. Water until it runs out the bottom, then leave it alone until the top 2 to 3 cm are dry again. In midsummer on the Highveld that is once a day for a 40 cm pot and twice for anything smaller. In a Cape summer with the south-easter blowing it can be more, and in winter here it might be once a week.

The RHS growing guide for lettuce is candid about what hot, dry weather does to it: the plant bolts, throws a flower stalk and turns bitter. Keep greens evenly moist and lightly shaded in summer and re-sow small batches every three weeks rather than one big planting. A 3 cm mulch of bark or straw on the soil surface cuts evaporation noticeably, which matters when water restrictions arrive, and grey water from the bath is fine on vegetables you cook.

Feeding, because watering washes food out

Every time water runs out of a drainage hole it carries dissolved nutrients with it, so a pot needs feeding in a way a bed does not. Mix a slow-release fertiliser into the potting soil at planting, then start a liquid feed every two weeks once plants are growing strongly. For leafy greens use something higher in nitrogen; for tomatoes and peppers switch to a feed with more potassium when flowers appear, or you get a lush green bush with nothing on it. Feed onto damp soil, never dry, or you scorch fine roots. Every fourth watering, water with plain water only to flush salts through.

Buy seedlings or sow seed?

For a first season, buy seedlings of tomatoes, peppers and brinjals, because they need a long warm run and seed sown in September in a pot loses six weeks. Sow lettuce, rocket, radishes, beans, beetroot and coriander directly into the trough, because they germinate fast and transplant badly. Harden new seedlings off for three or four days in light shade before they go into full sun, and plant in the late afternoon so the first night is gentle. Our article on when and how to plant seedlings covers spacing and settling in, and 5 easy herbs to grow in pots is the natural companion, because a trough of tomatoes with basil and parsley at its feet is the most productive square metre most homes have.

Start with one deep trough in the sunniest spot you own, fill it with proper potting soil, and plant what the season allows. Get that right for one summer and the second trough will follow on its own. The pots we cast for edibles are grouped in one place, sized by depth so you can match them to the crops above, and you can find the right depth for your vegetables here.

Frequently asked questions

When should I plant tomatoes in pots in South Africa?

On the Highveld, plant tomato seedlings from mid September once frost has passed and night temperatures stay above about 16 degrees. In coastal KwaZulu-Natal they can go in most of the year, and in the Cape spring planting after the winter rains works best.

How deep should a pot be for vegetables?

Lettuce, spinach and herbs need 20 cm of soil, carrots and beetroot 30 cm, and tomatoes, peppers and brinjals 40 cm or more. Deeper pots also stay moist far longer in summer heat.

How many hours of sun do vegetables in containers need?

Fruiting crops like tomatoes, peppers and beans need at least six hours of direct sun and prefer eight. Leafy greens and most herbs manage on four hours and appreciate afternoon shade in midsummer.

Can I use garden soil in vegetable pots?

No. Garden soil compacts, drains poorly and brings weeds and pests into the pot. Use a bark-based potting soil made for containers and mix in compost for hungry crops like tomatoes.

How often should I water vegetables in pots?

In Highveld midsummer, once a day for a 40 cm pot and twice for smaller ones, early in the morning, until water runs out the bottom. Let the top 2 to 3 cm dry before watering again, and expect once a week or less in winter.