Growing Herbs in Small Pots Successfully

There is a particular disappointment that comes from a supermarket basil plant: three glorious weeks on the windowsill, then a yellowing, woody stump. The herb was never the problem. The pot was. Small containers hold very little compost, which means very little buffer between a plant and your mistakes, and herbs are quick to punish both drought and drowning. Get the drainage sharp and the watering rhythm tied to the weather, though, and a 15cm pot can keep cropping from late spring well into autumn.

Drainage is the whole foundation

Roots need air as much as they need water, and in a small pot the two compete for the same space. If water sits in the base, roots rot and the plant collapses seemingly overnight. So start with drainage and refuse to compromise on it.

• Choose a pot with at least three drainage holes, or drill extra ones. A single central hole in a wide pot leaves the outer compost permanently sodden.
• Skip the layer of gravel or broken crocks at the bottom. It raises the water table inside the pot rather than improving flow. A single piece of broken pot over the hole to stop compost washing out is plenty.
• Empty saucers after rain and never leave a pot standing in a puddle. If you use a saucer indoors, add a layer of grit so the base of the compost sits clear of any water.
• Terracotta breathes, wicking moisture through the walls and drying out faster. Plastic and glazed pots hold on to water for longer. Unglazed terracotta suits thyme and rosemary; plastic suits basil and mint.
• Raise pots onto feet or a couple of battens so air can move underneath. On a paved patio this alone prevents a great deal of trouble.

Right pot, right compost

As a rough rule, allow about one litre of compost per herb plant, and go a size up for anything vigorous. A 15–20cm pot suits a single basil or thyme plant comfortably; mint will fill a 25cm pot and ask for more by August. Overpotting is a real risk with small herbs, because a large volume of compost around a small root ball stays wet for too long.

For basil and mint, a good peat-free multi-purpose compost is fine, perhaps with a handful of perlite stirred through. For thyme, oregano, sage and rosemary, mix in 20–25 per cent horticultural grit by volume, and add a teaspoon of garden lime to the pot if your tap water is soft. Mediterranean herbs want lean, sharp, fast-draining conditions, and they sulk in rich, soggy compost.

Three herbs, three very different thirsts

Treating every pot the same is the most common mistake. Basil is a soft, fast-growing leaf machine that wants steady moisture, warmth and plenty of light. Let it dry out fully and it will bolt to flower and turn bitter within days. Water it when the surface just begins to feel dry, and keep it out of cold draughts — below about 10°C it stops growing altogether.

Mint is the thirstiest of the three and the least fussy about light. It will happily sit in semi-shade and drinks far more than you expect, especially in a terracotta pot on a sunny day. It also runs, so keep it in its own container rather than sharing. If you want a continuous supply, plant a few pots and rotate which one you pick from.

Thyme is the opposite creature entirely. It wants to dry out between waterings, hates having its feet wet, and prefers full sun and poor, gritty soil. Water it thoroughly, then leave it alone until the compost is dry a couple of centimetres down. A thyme that is watered like basil will be dead by midsummer, and it will look fine right up until it isn't.

Water to the weather, not the calendar

A timetable is worse than useless because it cannot see the sky. In a hot, breezy July, a small terracotta pot of mint may need water twice a day. In a cool, damp week in September, the same pot may need nothing at all. Judge each pot individually.

• Lift the pot. A dry pot is startlingly light. Learn the weight when wet and when dry and you will rarely get it wrong.
• Use a finger. Push a finger in up to the second knuckle. Water only if it feels dry at that depth, and for thyme, only if it feels dry a little deeper still.
• Water in the morning where you can. Plants drink through the day, and foliage that stays wet overnight invites mildew.
• Water until it runs out of the bottom, then stop. Little and often wets only the top layer and encourages shallow, fragile roots.
• After heavy rain, check saucers and trays and tip them out. Winter and early spring watering should be minimal, especially for woody herbs.

Feeding, pinching and keeping the crop going

Compost nutrients run out after roughly six weeks in a small pot, so begin a weak liquid feed then. Basil and mint appreciate a balanced feed every fortnight, or a tomato feed once they are cropping hard. Thyme, rosemary and sage need very little — one light feed a month at most, or they will grow soft and floppy and lose their flavour.

Pinching out is what turns a single supermarket plant into a season-long supply. Take the growing tips of basil regularly, always above a pair of leaves, and never strip more than a third of the plant at once. Remove mint flowers as they appear to keep the leaves tender. Thyme rewards a trim after flowering but resents being cut back into old, leafless wood — stay within the green growth.

Sow or buy fresh plants in succession, a few weeks apart, so you always have a young, vigorous pot coming on behind the tired one. Two or three small pots at different stages will out-crop one large one every time, and there is nothing quite like stepping outside with a pair of scissors to lift a whole meal.