A pot on a patio is a small, closed world. You decide how much root room a plant gets, what it grows in, and how often it drinks — and those three decisions explain most of what goes right or wrong in container growing. Choose a pot that is too small, fill it with heavy garden soil and water it in timid little dribs, and even a tough pelargonium will look tired by August. Get the basics roughly right, though, and container planting is remarkably forgiving.
None of it is complicated. It just helps to think about the pot before you fall for the plant.
Pot size: buy bigger than you think
The classic beginner's mistake is a pot that looks generous in the garden centre and turns out to be too small by July. Root volume is a buffer: the more compost a plant has around its roots, the more water and nutrients it can draw on between your visits with the watering can. A cramped pot dries out in an afternoon of sun and forces you to water twice a day in a heatwave.
As a rough guide:
- 20–25cm across: thyme, chives, parsley and most bedding plants
- 30–40cm: bush tomatoes, peppers, pelargoniums, flowering annuals
- 45cm and up: cordon tomatoes, courgettes, bay, blueberry, small shrubs
- 50cm or a half-barrel: compact trees and large shrubs, which will need repotting every few years
Depth matters as much as width. Carrots want a long tom; anything top-heavy needs enough weight in the base not to blow over. Where you can, plant straight into the pot the plant will finish in, because roots dislike being disturbed twice. One more practical point: a large pot full of damp compost is heavy. If it is going on a balcony, check it can take the load — your landlord or managing agent is the person to ask.
Drainage: the hole is doing the work
The most important feature of any container is a drainage hole. Without one, water collects at the bottom, roots sit in it, and the plant slowly suffocates.
You will still see advice about putting broken pots or a layer of gravel in the base "for drainage". It does not work: it simply raises the saturated layer closer to the roots. Use a free-draining compost and let the water leave through the bottom.
- One generous hole, or several smaller ones, kept clear of compost and roots
- Pot feet, tiles or battens to lift the pot off paving so it does not seal itself shut
- Saucers are fine for catching run-off, but empty them rather than leaving roots standing in water
- Check the holes in spring — they block easily as roots grow
- A pot with no holes is a cachepot: sit a nursery pot inside it and take that out to water
A piece of mesh or slate over the hole stops compost washing out. It will not improve drainage, and it is not meant to.
Compost: what to fill it with
Garden soil is not a potting compost. In a container it compacts, drains badly, dries into a brick and can bring weeds and pests with it. Buy compost instead, and choose it for the job.
Peat-free multipurpose suits most annuals, vegetables and herbs. Loam-based compost such as John Innes No. 2 is heavier and holds nutrients and moisture for longer, which makes it a better home for bay, rosemary and shrubs that will stay put. Ericaceous compost is essential for acid lovers: blueberries, camellias, rhododendrons, heathers and pieris.
For Mediterranean herbs and anything that sulks in wet compost, mix in grit or perlite. A simple blend that works for most pots:
- Three parts peat-free multipurpose compost
- One part horticultural grit or perlite
- Slow-release fertiliser at the rate on the packet
Use fresh compost for annuals each year. For perennials, scrape off the top few centimetres, replace it, and repot into a larger pot every couple of years. Old compost can harbour vine weevil grubs, so do not simply reuse it for the same plant.
Watering: thoroughly, then wait
Watering "little and often" is the cause of a great many container casualties. Small amounts only wet the top of the compost, so roots stay shallow — and shallow roots need watering more often, not less.
Do the opposite. Water slowly until it runs out of the drainage hole, then leave the pot alone until the top two or three centimetres of compost are dry. Push a finger in to check, or lift the pot: a well-watered one feels surprisingly heavy. In summer, most patio containers need this daily and sometimes twice; in spring and autumn, every few days; in winter, rarely — though evergreens in a sheltered spot may still want a drink in a mild, dry spell.
- Underwatered: compost shrunk away from the sides, water running straight down the gap, crisp brown leaf edges, drooping that has not recovered by evening
- Overwatered: yellowing lower leaves, soggy or sour-smelling compost, fungus gnats, and wilting despite wet compost — a sign the roots are rotting
Water in the morning if you can. If compost has dried out completely, it repels water, so soak the pot in a bucket for twenty minutes or water it in two or three slow passes. A gravel or bark mulch on the surface slows evaporation, and grouping pots together gives them a little shade.
Feeding: the nutrients run out
Compost feeds a plant for a few weeks, then it is down to you. Mix slow-release granules into the compost at planting for anything long-term, and use a liquid feed weekly through the growing season for tomatoes, peppers, courgettes and flowering annuals once buds appear. Herbs grown for their leaves need very little — too much feed gives soft, bland growth. Never feed a dry plant; water it first.
A first pot, step by step
Choose a pot at least a third larger than the one the plant came in, and larger still for anything permanent.
- Check the drainage hole and stand the pot on feet.
- Fill it a third full with compost and firm it gently.
- Sit the plant in so the top of its rootball is 2–3cm below the rim.
- Fill around it, firming as you go, and leave that gap for water.
- Water slowly until it runs out of the bottom.
- Top-dress with gravel and put it where you will see it.
After that the routine is simple: check daily in summer, water thoroughly when the surface is dry, feed weekly while things are growing, and empty the saucer. Do that and your pots will keep going long after most patios have given up.
Photo: kalcommodore / Pixabay
