Why a Balcony Makes a Surprisingly Good Herb Garden

Herbs are among the most generous plants you can grow in a confined space. They are mostly shallow-rooted, they cope with being crowded, and the more you pick them, the more they produce. A balcony with four to six hours of sun can easily supply mint for summer drinks, basil for pasta, and rosemary for roast potatoes.

What you cannot do is treat a collection of pots as though it were a small patch of garden. Pots dry out far faster than soil in the ground, their nutrients wash away with every watering, and on a balcony they are exposed to wind that strips moisture from leaves and compost alike. Get those three things right and the rest is straightforward.

Choosing the Right Containers

Size is the single biggest factor in how forgiving a pot will be. Small pots look charming and fail quickly. As a rule, give each herb a container at least 20cm across and 20cm deep, and go larger for anything woody.

• Rosemary, sage and thyme: 30cm pots or bigger. They build substantial root systems and resent being cramped.
• Basil, parsley and coriander: 20–25cm is plenty, but they drink fast, so bigger means less frantic watering.
• Mint: always its own pot, 25–30cm wide. It spreads by underground runners and will smother anything sharing its compost.

Make sure every pot has drainage holes and keep them clear — do not cover them with a layer of crocks, which simply raises the waterlogged zone. Terracotta looks lovely but dries out quickly, plastic is light and cheap but can blow over in a gust, and glazed ceramic holds moisture well but adds weight. Whichever you choose, stand pots on feet or stones so water can escape freely.

Grouping pots together creates a microclimate, shelters foliage from wind, and makes watering quicker. If your balcony is exposed, weight the base of lighter pots with a few stones or a brick.

Compost, Drainage and Feeding

Use a peat-free multipurpose compost for most herbs, but adjust it to suit the plant. Mediterranean herbs — rosemary, thyme, oregano and sage — hate sitting in wet compost, so mix in roughly a quarter horticultural grit or perlite by volume. Basil prefers something richer; a loam-based compost or a handful of worm castings mixed through will keep it lush.

Never use garden soil in pots. It compacts, drains badly and brings in pests. Add slow-release granules at planting time, then top up the top two or three centimetres of compost each spring, or repot into fresh compost every other year.

Feeding needs a light touch. From April to September, give a liquid seaweed or tomato feed every fortnight — basil and mint appreciate it. Rosemary and thyme need far less; overfeeding them produces soft, sappy growth with much less flavour.

Watering: The Habit That Decides Everything

More herbs are killed by inconsistent watering than by anything else. In high summer, a small pot on a sunny, breezy balcony may need water every day, and occasionally twice. Check by pushing a finger two centimetres into the compost, or simply by lifting the pot — a light pot is a dry pot.

Water thoroughly until it runs out of the drainage holes, ideally in the morning or early evening. Rainwater is ideal if you can collect it, though tap water is perfectly acceptable. Saucers are useful during heatwaves, but empty them an hour later; standing in water will rot rosemary and thyme within weeks. Mint is the exception and is happy in consistently damp compost.

If you are away often, self-watering pots or a simple drip system will save you a great deal of guilt.

Light, Position and Problem Solving

A south or west-facing balcony with six or more hours of sun suits basil, rosemary, thyme and oregano. East-facing spots are ideal for parsley, chives and mint, which prefer a little shelter from the fiercest midday sun. Even a north-facing balcony can produce chives, parsley and chervil, just more slowly.

Turn pots a quarter turn each week so plants grow evenly rather than leaning towards the light. Watch for aphids and whitefly on the undersides of leaves; a firm jet of water usually deals with a light infestation, and a diluted soap spray handles the rest.

Keeping the Harvest Coming

Pick little and often, and never strip more than a third of a plant at once. Pinch out the growing tips of basil above a pair of leaves to encourage bushy growth, and remove flower buds as soon as they appear — once basil or coriander bolts, the leaves turn bitter. Cut mint back hard to about 5cm to keep fresh, tender growth coming.

Sow small batches of basil, coriander and parsley every three to four weeks through spring and summer for a continuous supply, and buy rosemary, thyme and sage as young plants in spring; looked after well, they will last for years. In winter, cut back watering, stop feeding, move pots against a sheltered wall and raise them onto feet. Mint will die back and return reliably in spring.