Container gardening: grow more in pots

The single biggest mistake in container gardening is using too small a pot. Everything else — feeding, watering, positioning — is much easier to get right once the container is big enough to hold the crop it's growing.

Choosing containers: size, drainage and material

Container size is the most critical variable. Larger containers hold more compost, which holds more moisture and nutrients, and gives roots more room to grow. The result is a plant that needs less watering, less feeding, and suffers less stress. General guidance on minimum sizes:

• Salad leaves, radishes, herbs, spring onions: any container at least 15 cm deep. Window boxes, recycled tins, old colanders — all work fine for these shallow-rooted crops.
• Tomatoes, peppers, chillies, aubergines: a minimum of a 30–40 cm pot, or a standard-size grow bag (typically around 30–35 litres). Bigger is better — a 50-litre pot gives significantly more consistent results.
• Dwarf French beans, chard, spinach, courgettes: 25–30 cm minimum depth and width; courgettes prefer larger still (40+ cm).
• Potatoes: deep containers of at least 40–50 cm, or purpose-made potato bags — you need room to earth up the stems as they grow, which is where the tubers form.
• Strawberries: strawberry planters with multiple pockets work, or standard 25–30 cm pots with three to four plants.

Drainage is non-negotiable. Every container must have drainage holes at the bottom. Roots sitting in waterlogged compost rot, and no amount of good care will save a plant with a waterlogged root system. If you like a decorative pot without holes, use it as an outer sleeve and keep the plant in a plain functional pot inside it — just remember to empty any water that collects at the bottom.

On materials: terracotta is beautiful and breathes well, which is good for plant roots — but it also loses water quickly and is heavy. Plastic retains moisture better and is lightweight, making it practical for balconies with weight limits. Fabric pots (fabric grow bags) are increasingly popular — they air-prune roots naturally, preventing root circling, and can be folded away in winter. Upcycled containers — old wooden crates lined with hessian, half-barrels, metal buckets with holes drilled in — work well and cost nothing beyond drilling a few drainage holes.

The right compost mix

Garden soil is not suitable for containers — it compacts into an almost solid mass, drains poorly and frequently introduces weeds, pests and diseases. Use a purpose-made compost, and choose peat-free: peat-free composts have improved considerably and are the sustainable choice.

A good general-purpose peat-free multipurpose compost is suitable for most container crops. For vegetables, look for one with added slow-release fertiliser, or plan to start supplementary feeding after six to eight weeks (when the initial nutrient charge runs out). For improving drainage and preventing compaction, mixing in a proportion of grit, perlite or composted bark — roughly one part in four or five — makes a meaningful difference, especially in containers that will be used for more than one season.

For tomatoes, peppers and other heavy-feeding crops, a specialist tomato or vegetable compost gives a better start. You can also use homemade garden compost mixed with bought compost to reduce cost and boost organic matter — see our composting at home guide for how to make your own.

Watering: pots dry out fast

Containers dry out much faster than open ground, because there is a limited volume of compost, no connection to sub-surface moisture, and the pot itself (especially terracotta) can lose water through its walls. In warm weather with a large plant in full growth, a pot may need watering daily — sometimes twice a day.

The most reliable way to check: push a finger 2–3 cm into the compost surface. If it feels dry, water. If it still feels moist, leave it. Overwatering is a problem too — compost that never dries slightly at the surface can become waterlogged and deprive roots of oxygen.

When you water, water thoroughly — until water runs freely from the drainage holes. Light surface watering encourages roots to stay near the surface where they dry out most quickly. A thorough soaking draws roots deeper into the compost where moisture is more stable.

Strategies to reduce watering frequency:

• Self-watering containers have a reservoir at the base that the compost draws from as needed. Effective for salads, herbs and other shallow-rooted crops.
• Grouping pots together creates a localised humid microclimate and reduces how fast the compost dries out. It also makes watering a set of pots in one go much more practical.
• Mulching the surface — a layer of gravel, bark chips or compost over the top of the pot — slows evaporation significantly.
• Positioning pots out of hot afternoon sun in summer reduces the rate at which they dry out without sacrificing too much overall sunlight.
• Drip irrigation systems can be set up for a collection of containers and run from a timer — a genuinely practical option if you have many pots or travel regularly.

For a broader look at saving water in the garden, see our water-wise gardening guide.

Feeding container crops

The compost in a container contains a finite quantity of nutrients. Once those are used — typically within six to eight weeks of planting — the plant has no way to access more unless you supply them. This is one of the main differences between container growing and open ground: you must feed regularly.

• Liquid feeds are the most controllable option. Applied weekly or fortnightly with watering, they give you precise control over what the plant receives. Use a balanced liquid feed early in the season for leafy growth, and switch to a high-potassium feed (such as a tomato feed) once flowering and fruiting begins. Tomato liquid feed works well for all fruiting crops — tomatoes, peppers, courgettes, strawberries.
• Slow-release granule fertilisers can be mixed into the compost at planting or top-dressed onto the surface. They release nutrients gradually over several months, reducing the need for frequent liquid feeding. They work well as a base layer, with liquid feeding on top during peak growth.
• Homemade liquid feeds: comfrey liquid (made by steeping comfrey leaves in water) is high in potassium and an excellent home-produced feed for fruiting crops. Nettle liquid feed is higher in nitrogen, better for leafy crops early in the season.

Best crops for containers

Most vegetables can be grown in containers given the right size pot — but some are particularly suited and reliable:

• Tomatoes: one of the best container crops, especially cherry varieties like 'Tumbling Tom' (which trails), 'Maskotka' or 'Sweet Million'. Bush varieties need less support and less pruning than cordon types.
• Chillies and peppers: thrive in containers, especially in a sunny, sheltered spot or on a windowsill. Pot them up in a good compost and they're highly productive relative to space.
• Salad leaves and spinach: fast-growing, shallow-rooted and ideal for window boxes or small pots on windowsills. Sow successionally — a new small pot every few weeks — for a continuous harvest.
• Herbs: mint (which should always be confined to a pot to prevent it spreading), basil, parsley, chives, thyme, rosemary — all do well in containers and are useful in the kitchen.
• Dwarf French beans: compact enough for a 25–30 cm pot, productive, and easy. Sow directly into the pot in late spring.
• Strawberries: excellent in strawberry planters, hanging baskets or standard pots. Runners are free; one initial purchase can provide plants for years.
• Potatoes: grow early ('new potato') varieties in deep containers or fabric potato bags. Harvest is clean and easy — tip out the whole pot rather than digging.
• Courgettes: productive in a large (40+ litre) container, but they do need consistent watering and feeding and take up significant space.

Positioning and sun

Most vegetable crops need a minimum of six hours of direct sunlight a day. A sheltered, south-facing wall (north-facing in the Southern Hemisphere) is the best spot for fruiting crops — tomatoes, peppers, courgettes — which need the most warmth. Leafy crops and herbs tolerate partial shade and can go in less sunny spots.

Avoid placing pots in positions exposed to strong prevailing wind. Wind increases moisture loss from both the pot and the plant, and can physically damage stems and flowers. A fence, wall or hedge providing shelter on the windward side makes a meaningful difference to both growth and watering needs.

One of the real advantages of containers is movability. Early in the season, bring pots under cover or against the house on cold nights to protect from frost. Later, move them to track the sun. Move tender plants — chillies, basil — indoors in autumn to extend the harvest season.

Overwintering pots

Outdoor containers face specific risks in winter that in-ground plants do not:

• Frost cracking terracotta: if water in the compost freezes and expands, it can crack terracotta and ceramic pots. Move valuable pots into a shed or garage for winter, or wrap them with hessian or bubble wrap if they must stay outside.
• Root damage in small pots: the roots of hardy plants can still freeze solid in a small container even when the soil around the same plant in the ground would not. Grouping pots together, insulating with straw or fleece, or moving them under shelter protects roots.
• Overwintering herbs: rosemary, thyme and sage survive frost in the ground but are more vulnerable in pots — move them to a sheltered spot or unheated greenhouse if hard frosts are expected. Mint dies back to the roots in winter and returns in spring; leave it in its pot.
• Emptying annual pots: once tender crops like tomatoes and basil are finished, empty the pot, compost the old plant material, and store the compost separately for mixing into next year's planting (see below).

Refreshing compost yearly

Compost that has grown a crop through a full season is nutritionally depleted and often physically degraded — it becomes compacted, loses its open structure, and may contain pest eggs or fungal spores from the previous crop. Starting with fresh or refreshed compost each year gives the new crop the best possible start.

Used compost is not wasted. Spread it as a mulch on garden beds, mix it into new compost at up to a third of the total volume, or add it to a compost heap to break down further. For large containers — a 50-litre pot of tomato compost — topping up with fresh compost and adding a slow-release fertiliser is a practical middle ground if buying entirely fresh each year is not practical.

How to plant up a container

1. Choose the right size container. For the crop you're growing, err on the side of larger. Check that drainage holes are clear; add them if not.
2. Add a layer of crocks or grit to the base. Broken pot shards, coarse gravel or a piece of mesh over the drainage holes prevent compost from washing out while keeping drainage clear.
3. Mix your compost. Combine peat-free multipurpose compost with a small amount of perlite or grit for drainage. Add a slow-release fertiliser if not already included in the compost.
4. Fill to within 3 cm of the rim. Firm gently but don't compact. Leave the watering reservoir gap at the top.
5. Plant at the right depth and water in thoroughly. For transplants, plant at the same level as they were in the original pot (or deeper for tomatoes, which form roots along buried stems). Water until it flows freely from the base.
6. Position in the right spot. Fruiting crops in the sunniest, most sheltered location; leafy crops can tolerate partial shade.
7. Begin a feeding regime after six to eight weeks. Once the initial compost nutrients are used up, switch to a weekly liquid feed appropriate to the crop.

Container gardening checklist

• Container large enough for the crop — bigger is almost always better.
• Drainage holes clear and functioning.
• Good peat-free compost mixed with grit or perlite for drainage.
• Slow-release fertiliser added at planting.
• Plants watered in thoroughly after planting.
• Positioned in adequate sunlight for the crop.
• Daily watering checks in warm weather; watered thoroughly when needed.
• Liquid feeding started after six to eight weeks and continued throughout the season.
• Plan in place for overwintering pots that stay outside.
• Compost refreshed or replaced at the start of each new season.