Indoor Herb Garden Guide

Almost everyone starts the same way: a pot of supermarket basil on the windowsill, dead within three weeks. The failure is so consistent that people conclude herbs do not grow indoors. They do. The supermarket pot is not a plant, it is a product, and treating it like one is the mistake.

Why Supermarket Herb Pots Die

That pot holds thirty to seventy seedlings crammed into about 250 ml of compost, grown in a glasshouse at high light and humidity, force-fed, and shipped to be eaten within a fortnight. It is a bouquet with roots.

• Root competition. Fifty seedlings sharing a teacup of compost exhaust water and nutrients within days. Any one alone would be fine.
• A light crash. The plant moved to a kitchen at perhaps five percent of glasshouse intensity, and cannot support the leaf area it grew.
• Watering by guesswork. The pot dries out in a day, so people overcompensate and it stays saturated. Stems collapsing at soil level is damping off, not thirst.

The fix takes ten minutes. Tip the pot out, divide the root mass into three or four clumps of a dozen seedlings, and pot each into a 12 to 13 cm (5 in) pot of fresh compost. Three usually survive. Pinch the tips a week later to force branching.

Choosing a Spot: Light Comes First

Indoor herbs rarely fail from cold or bad compost. They fail from light. A sunny windowsill might see 10,000 lux for a few hours, while an overcast day outside is 20,000 and full sun over 80,000.

In the northern hemisphere, south is best, east and west are workable for tougher herbs, and north grows nothing but mint and chives, badly. Reverse this below the equator.

One quick test: at midday, hold your hand 30 cm above the sill. A soft-edged or barely visible shadow means it is too dark for basil or thyme.

If your best window is mediocre, a grow light fixes it cheaply. A 20 to 30 watt LED bar hung 20 to 30 cm above the pots, on a timer for 12 to 14 hours a day, covers six herbs. Do not run lights around the clock; plants need a dark period.

The Six Herbs Most Worth Growing Indoors

Mediterranean woody herbs want more light than most homes provide; leafy annuals and tough perennials are the reliable set.

Parsley and coriander send down a taproot, so depth matters more than width and a shallow pot stalls them. Skip rosemary, which hates dry indoor air, and sage and oregano, which go leggy below six hours of sun.

Pots, Mix and Drainage

Every pot needs a drainage hole; indoors there is no sun or wind to dry a saturated pot. If your container has none, use it as a cachepot.

Size up from what herbs arrive in. A 13 to 18 cm pot buffers a couple of days of neglect; a 9 cm pot dries out overnight on a sunny sill. There is more on volumes in container sizes for tomatoes, peppers and herbs.

Use peat-free compost with about 20 percent perlite, or half compost and half grit for thyme, which rots more readily than it dries out. Tip out saucers fifteen minutes after watering; a pot standing permanently in water loses its roots within a month.

Watering Indoors Without Drowning Roots

Overwatering kills more indoor herbs than drought, but the mechanism is misunderstood. It is not the volume, it is the frequency: constantly wet compost holds no air, so roots suffocate and rot.

Use the finger test. Push a finger 2 to 3 cm in; if it feels damp, wait, and if it is dry, water until it runs from the bottom. In winter that might be weekly; on a sunny sill in July, daily.

1. Water in the morning, so the surface dries before the cooler night.
2. Use room-temperature water, because cold tap water visibly checks basil.
3. Bottom-water fussy plants in 2 cm of water for ten minutes, keeping the crown of parsley dry.
4. Group pots together, since humidity between them is higher.

Do not mist. It does almost nothing for humidity and it does encourage mildew.

Feeding and Repotting

Fresh compost carries roughly six weeks of nutrients. After that a herb lives on what you give it.

Feed fortnightly from week six with a balanced liquid feed at half the recommended strength. Half strength twice as often beats full strength monthly and avoids the salt build-up that shows as white crust and brown leaf tips.

Herbs grown hard taste better; heavily fed basil makes big soft leaves with less aroma. Feed for health, not size, following the soil and fertiliser basics guide.

Repot when roots circle the drainage hole, typically every 12 to 18 months, and go up one size only; a plant in a far larger pot sits in cold wet compost it cannot use.

Harvesting So Plants Keep Producing

How you cut decides whether a herb lasts a month or a year. For leafy herbs, remove whole stems rather than individual leaves.

With basil, cut just above a pair of leaves, taking the top third; two shoots grow from that junction, so the plant doubles its branching each time. With parsley and coriander, take outer stalks at the base, since new growth comes from the centre. With chives and mint, cut low and hard; chives snipped to 5 cm regrow in two to three weeks.

Never take more than a third at once, and pinch out flower buds; once basil flowers, leaf production stops and flavour turns bitter. If you already plan an outdoor patch, Vegarden will keep the windowsill pots in the same plan.

Common Indoor Herb Problems

Long pale stems with wide gaps between leaves. Not enough light. Move it brighter, then cut back by a third so new growth comes in compact.

Lower leaves yellowing while compost stays wet. Overwatering or a blocked hole. Let it dry to 3 cm depth and reduce frequency, not volume.

Brown crispy leaf tips. Dry air or salt build-up. Group pots together, and flush the compost if white crust shows on the surface.

Sticky leaves and tiny green insects. Aphids, which thrive indoors with no predators. Spray with washing-up liquid at 5 ml per litre, rinse after an hour, and repeat weekly for three weeks.

Fine webbing and stippled yellowing. Spider mite, which loves warm dry rooms. Group pots to raise humidity and rinse under a tepid shower.

Small black flies. Fungus gnats, a symptom of permanently damp compost. Let the surface dry between waterings and top the pot with grit.

If a herb is struggling and you are unsure why, assume light before anything else. It is the cause roughly three times out of four.

Get the light right, water on the finger test and cut whole stems, and a windowsill will keep you in herbs most of the year.