Best Soil for Herbs: Drainage, Texture and pH

Herbs have a reputation for growing in poor ground, and there is some truth in it. The best soil for herbs is not the richest or darkest soil in the yard. It is soil that lets water pass through and leaves roots some air.

That makes the question of whether your garden soil is good enough fairly easy to answer. Check drainage first, then texture, then pH, and fix only what the checks show.

Drainage matters most

Nearly every culinary herb asks for well-drained soil, and sage and rosemary in particular dislike wet, poorly drained ground. The reason is simple: roots need air as well as water. Soil is full of small spaces, and after rain or watering those spaces should drain so that air can move back in. Where they stay filled with water, roots struggle and often rot.

Poor drainage is also the hardest fault to correct once plants are in, which is why it is worth checking before anything else.

A simple drainage check

You can get a rough idea of how your soil drains with a spade and a bucket of water.

1. Dig a hole about 12 in (30 cm) deep and about as wide.
2. Fill it with water and let it drain away completely. This wets the surrounding soil so the second filling gives a fairer reading.
3. Fill the hole again and note how long the water takes to disappear.

If the second filling is gone within a few hours, drainage is good enough for most herbs. If water is still standing the next day, the spot drains poorly and you will need to raise the planting level or choose another place.

Treat this as a rough test, not a measurement. The result shifts with the season and with how wet the ground already was. Watching where puddles linger after a heavy rain tells you much the same thing.

Texture: loam, clay and sand

Texture describes the mix of particle sizes in soil, from coarse sand to very fine clay. You can judge it roughly by hand: take a moist handful, squeeze it and rub a little between your fingers.

Notice that compost appears twice. In clay it helps the fine particles clump into crumbs with spaces between them. In sand it acts like a sponge, holding water that would otherwise run straight through. Either way, use finished compost that is dark, crumbly and earthy-smelling.

In heavy clay, compost alone may not be enough. Planting a few inches above the surrounding ground, in a mounded or raised bed, lets extra water drain away from the roots. The steps are in the guide on how to prepare a garden bed for herbs.

Soil pH and why a test beats a guess

pH is a measure of how acidic or alkaline soil is, and it affects how easily plants can take up nutrients. Most herbs grow in slightly acidic to neutral soil, which is what many garden soils already are.

You cannot tell pH by looking. A soil test from a local extension lab tells you the pH and the nutrient levels, usually with recommendations for what to add, if anything. For how to take a sample and find a lab, see the University of Maryland Extension page on soil testing.

If you are starting a new bed, test before you plant. It is far easier to mix something into bare soil than to work around established herbs.

Fertility: moderate, not rich

Herbs generally need moderate soil, not rich soil. In very fertile ground many of them grow fast and soft, with plenty of leaf but often less flavor, and the stems can flop.

For most garden beds, a modest layer of compost mixed in before planting supplies what herbs need for the season. Whether you need anything more depends on the herb, on how often you cut it and on what a soil test shows. The guide to fertilizing herbs explains when feeding helps and when it works against you.

Mediterranean herbs and leafy herbs want different ground

Not all herbs want quite the same thing, and the split follows two familiar groups.

Rosemary, thyme, sage and oregano

These Mediterranean herbs prefer leaner, drier ground. Give them the best-drained part of the bed, go easy on the compost and avoid low spots where water gathers. Thyme is the clearest example: it performs best in dry, sandy or rocky soil, as the guide on how to grow thyme describes.

Basil and parsley

Soft, leafy herbs still need drainage, but they want soil that stays evenly moist and has a little more organic matter. A slightly more generous helping of compost suits them, along with a mulch once they are growing.

If your bed has a higher, drier end and a lower, moister end, you already know where each group goes.

What to fix first

When the checks turn up more than one problem, work in this order:

1. Drainage. If water stands, raise the bed or move it. Nothing else makes up for wet roots.
2. Texture. Mix compost into clay or sandy soil across the whole bed, not just into individual planting holes.
3. pH. Get a soil test and adjust only if the report recommends it.
4. Fertility. Leave this for last. In most beds the compost has already taken care of it.

One exception to all of this: herbs in pots. Garden soil packs down in a container, so use a potting mix made for containers there instead.

Soil improves slowly, and it does not need to be perfect on planting day. Get the drainage right, add compost, test when you can, and your herbs will have what they need to settle in.