Soil and drainage for herbs

01Start with drainage

Drainage is the first question, and it is more important than fertility. Mediterranean herbs — rosemary, lavender, thyme, oregano, sage — evolved on thin, stony ground and rot in a wet winter. Moisture lovers — mint, nettle, lemon balm, schisandra — are the opposite. Putting them in the same bed means one group is always wrong.

Test drainage with a simple hole: dig a 30 cm deep, 30 cm wide pit, fill it with water, and let it drain. Refill it and measure how long the second fill takes to disappear. If more than a few hours pass, you have a drainage problem. The fix is raising the bed, adding grit and organic matter, or planting on a mound rather than fighting the subsoil; RHS drainage guidance follows the same logic (RHS).

02Texture and organic matter

Soil texture is the mix of sand, silt and clay. You cannot change it quickly, but you can improve its structure. Organic matter — compost, leaf mould, aged manure — binds sandy soil, opens clay soil and feeds the soil life that does the real work. Apply it as a mulch in autumn and let the worms incorporate it.

Do not dig wet clay. It smears into a pan that takes years to repair. Wait until the soil crumbles in your hand rather than forming a shiny ribbon. For a new herb bed on heavy ground, a raised bed 20–30 cm deep is often a better investment than repeated amendments.

Soil type	What it does	Best response
Sandy	Drains fast, dries out, low nutrients	Add compost and mulch; water more often; good for lavender and thyme
Clay	Holds water and nutrients, drains slowly	Raised beds, grit, organic matter; avoid winter digging
Silt	Fertile but compacts	Keep off it when wet; add organic matter; avoid heavy machinery
Loam	Balanced and workable	Maintain with compost; most herbs will grow

03pH without drama

Most herbs grow in a pH range of 6.0–7.5. Lavender, thyme and licorice tolerate or prefer alkaline soil; ginger and turmeric prefer slightly acid conditions; chamomile and fennel are unfussy. A simple soil test from a garden centre is enough to know whether you are close.

Do not chase perfect pH with chemicals. If the soil is far off, choose plants that suit it. Alkaline ground suits lavender, thyme and sage; acid ground suits blueberries, but not most of the herbs in this index. Compost and mulch buffer pH gently over time.

04Bed preparation by plant type

Prepare a bed for the group you intend to grow, not for a general “herb garden”. For Mediterranean herbs, remove weeds, add grit and compost, and plant on a slight mound. For moisture lovers, dig in leaf mould and plan for irrigation in dry spells. For roots, remove stones from the top 30–40 cm and avoid fresh manure, which causes forking.

Keep paths wide enough to work without stepping on the beds. Compaction is a quiet killer: it closes the pores that roots and water need. If you must stand on a bed, put a board down to spread the load.

05Mulch and the long game

Mulch after planting, when the soil is moist. A 5–8 cm layer of compost or leaf mould suppresses weeds, slows evaporation and feeds the soil. Keep it clear of stems and crowns to avoid rot. Gravel mulch suits lavender and thyme, and reflects heat; straw suits strawberries and garlic, but not the herbs in this index.

Feed the soil, not the plant. A bed that has been mulched annually for three years needs less watering, fewer weeds and less fertiliser than a bed that is dug and fed with soluble products. That is the long game, and it is the one that makes a herb garden feel established.

Sources & further reading

Horticultural guidance only. This site does not provide medical advice, doses or treatment plans. Written and edited by the Herb Ledger editorial team. Photo: : Laslovarga · CC BY-SA 4.0 · Wikimedia Commons

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