Choose the pot for the size the plant will reach, not the size of the seedling. Leafy greens and herbs manage in modest pots, fruiting vegetables need considerably more, and a dwarf fruit tree needs a very large one. A bigger pot also dries out more slowly, which matters most in an Australian summer.

The one exception is moving a plant up. Go one size at a time, so the roots can reach all the mix.

How big should the pot be for each type of plant?

The most useful published figures come from University of Illinois Extension, which lists minimum top diameters for common crops. They are in inches, so the metric conversions below are approximate. These are minimums for the crop itself, not a promise of a big harvest, and heat and watering in your climate can push you towards larger.

Sources: University of Illinois Extension for the crop sizes, and Organic Gardener for citrus.

If a plant’s label gives a mature height and spread, use that as your starting point. Where two sources disagree, go larger rather than smaller.

Why do small pots dry out so fast in summer?

The RHS notes that large containers dry out more slowly than small ones, and that shallow containers dry out quickly. A small volume of mix holds little water and warms through quickly.

In subtropical and tropical Australia, a pot on a hot balcony wall can need water daily from late spring. In temperate zones the same pot may only struggle during heatwaves. In arid regions, plan for larger pots from the start. The RHS says containers may need watering up to twice a day in hot weather, and the same applies to a small pot in an Australian heatwave.

Signs the pot is too small for the plant:

• The mix is dry again within a day of a thorough watering.
• Water runs straight out of the base without wetting the mix.
• Growth stalls or leaves wilt in the afternoon even though you watered that morning.

A bigger pot gives you a larger water reserve and a more stable root temperature. It is often a better fix than watering more often.

Does pot material make a difference?

Yes, mostly through water loss and heat. The table summarises what the sources say, plus clearly labelled editorial notes.

The University of Illinois Extension container materials page warns that dark containers exposed to intense summer sun can get hot, damaging roots and drying the mix quickly. In Australia, a dark pot against a north or west-facing wall is the classic problem. Pale colours, shade on the pot (not the foliage), or grouping pots so they shade each other all help.

Do pots need drainage holes?

Yes. The RHS states it is essential to have drainage holes in the base of a container. Without them, water collects and roots can rot.

A few practical points:

• Lift pots onto feet or bricks so the holes do not sit in a puddle. This also protects balcony floors.
• Empty saucers after watering, especially after rain.
• A magazine source (Organic Gardener) suggests that for large pots, one base hole may not be enough. Extra holes can be added in the sides, using a masonry or ceramic bit for terracotta and ceramic, or the pot can simply be raised.
• Avoid decorative outer pots with no holes unless the plant sits in a nursery pot inside and you empty the outer one.

How do you pot up without drowning the roots?

Move up in steps. The RHS advice is that the ideal pot is only slightly larger than the rootball, because an oversized pot holds excess compost that stays wet and can cause root rot.

1. Check the roots. If they circle the pot or push out of the holes, it is time.
2. Pick a pot only a little wider and deeper than the current one.
3. Loosen tight roots gently before planting.
4. Use fresh potting mix, not garden soil.
5. Water in well and keep the pot out of the hottest sun for a few days.

For timing, the RHS repotting advice says spring is a good time for most plants, early to midsummer works for many, and it is best to avoid autumn or winter when growth slows. Those are UK seasons. In the tropics and subtropics, growth runs for much of the year, but avoiding repotting in a heatwave is sensible. In cool and highland areas, repot as growth starts in spring.

An exception: for fast annuals such as lettuce, size the pot correctly from the start rather than potting up.

What about weight on a balcony?

A large pot full of wet mix is heavy, and a row of them adds up. This article gives no load figures because they depend on the structure. Before filling a balcony with big containers, ask the building owner, strata manager or landlord what is allowed. If you rent, you may need permission anyway.

Lighter plastic is easier to move than terracotta, as the RHS notes. You can also spread the load by using several mid-sized pots rather than one very large one, and keep heavy pots near walls rather than the outer edge. Both are editorial suggestions, not engineering advice. For layout ideas, see the complete guide to balcony gardening in Australia.

Common mistakes

• Buying a pot to suit the seedling, then watering daily all summer.
• Jumping from a small pot to a very large one.
• Putting a dark pot in full afternoon sun.
• Using a pot with no holes.
• Underestimating weight on a balcony.
• Choosing too small a pot for screening plants. If you want tall plants for privacy, see how pots can work as a living screen.

Quick checklist

• Look up the mature size of the plant.
• Pick the pot size from the table, going larger in hot, windy or sunny spots.
• Check drainage holes.
• Choose a pale or shaded pot for hot positions.
• Ask about weight limits.
• Pot up one size at a time.

For crop choices that suit these pots, read growing vegetables in containers.