Silty soil
A soil midway between sand and clay, often the most fertile and the easiest to work, but prone to compaction and surface capping.
Simple definition
Silty soil is dominated by silt, particles of intermediate size between sand (coarse) and clay (very fine). It is the soil of the great wheat plains (loess): supple, fertile, easy to work. Its downside: poorly structured, it compacts quickly and forms a surface cap that stops water infiltrating and seedlings emerging.
Visual and tactile appearance
Rubbed moist between the fingers it is soft, silky, almost floury; it does not really stick (neither the stubborn ball of clay nor the rough grain of sand). Dry, it crumbles to fine dust and its surface can set into a smooth cap after rain. Colour often beige to light brown.
Main properties
- A good compromise between water retention and drainage: neither the excess of clay nor the dryness of sand.
- Naturally fertile and easy to work as long as it stays covered.
- Little stability: it compacts quickly, especially worked or trodden when wet.
- Capping: under rain the surface seals, water runs off and seedlings emerge poorly.
Advantages in the garden
- Among the most productive soils: it is the earth of the great cereal regions.
- Easy to work and to sow; warms up reasonably in spring.
- Good water reserve while staying more free-draining than clay.
Limits & common problems
- Surface capping: the surface seals, hampers emergence and encourages run-off.
- Compacts quickly; sensitive to the compaction of repeated passages.
- Can lack cohesion and erode on slopes left bare.
- Lower exchange capacity than clay: elements leached a little faster.
Recommended improvements
- Never leave the soil bare: a permanent cover (mulch, green manure) protects against capping.
- Add organic matter regularly (compost, manure) to bind the particles into stable aggregates.
- Sow green manures with many roots (rye, phacelia, clover) that give the surface structure.
- Only work drained soil, never soaked; prefer the broadfork to digging.
- Create permanent beds so you no longer compact the cultivated soil.
- On slopes, keep a living cover to limit erosion.
Suitable plants
- Tomato
Fertile silt holds moisture while draining well: exactly the soil it asks for.
- Courgette
It needs a soil that is always moist and rich in compost, and silt holds water well.
- Lettuce
It wants a fertile soil that holds water: when dry, it bolts.
- Carrot
The root goes straight down in this fine, deep soil; just avoid treading on it, as silt compacts easily.
- Leek
It benefits from a fertile, well-drained soil enriched with compost.
- Cabbage
It finds in silt a fertile and fairly firm soil.
- Bean
A well-drained soil that holds a little water suits it, enriched with compost.
- Strawberry
It likes a fertile, well-drained soil, the profile of a good silt.
- Maize
It wants a fertile soil, and water when it flowers and then when its cobs swell: silt holds that reserve.
Plants to avoid or watch
- Lavender
To watch: silt holds water longer than it likes, and soil waterlogged in winter is fatal to it; a mound helps.
- Rosemary
To watch: it fears wet roots in winter; choose a well-drained spot or a raised bed.
- Thyme
To watch: it rots in soil that stays damp in winter; in moist silt, prefer a mound or a pot.
These reasons rely mostly on the RHS and on Plants For A Future, both in the United Kingdom: they describe an oceanic climate. In another climate, each plant's page gives its dates and advice for your climate zone.
Watering tips
Moderate watering: the water reserve is decent. The key is not quantity but protecting the surface, a mulch prevents the capping and keeps moisture. After heavy rain on bare soil, a light hoeing reopens the cap.
Guilds suited to this soil
These small plant groupings work particularly well on this type of soil.
Central
The Three Sisters
A classic Native American planting: three plants that support one another on the same mound.
Link with crop rotation
A versatile soil suited to almost every family. Alternate crops hungry for organic matter (Solanaceae, Cucurbitaceae), roots (carrot, beetroot) and legumes (pea, field bean); slip in a green manure as soon as a bed is free so the silt is never left bare.
Heavy metals: caution
Intermediate behaviour: silt fixes heavy metals less well than clay but better than sand. In an urban or old industrial context, an analysis is still recommended. See the Heavy metals concept and the Choosing and testing your ground guide.
Key takeaways
“Once I know my soil, I know what to plant, what to pair, what to improve and which guild to build.”
Sources
- RHS (Royal Horticultural Society) : Soil types (rhs.org.uk/soil-composts-mulches/soil-types)
- Baize, D. (2000). Guide des analyses en pédologie (2e éd.). Paris : INRA Éditions.
- Kabata-Pendias, A. (2011). Trace Elements in Soils and Plants (4e éd.). Boca Raton : CRC Press.
- RHS (Royal Horticultural Society) : How to grow tomatoes (rhs.org.uk/vegetables/tomatoes/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow courgettes (rhs.org.uk/vegetables/courgettes/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow lettuce (rhs.org.uk/vegetables/lettuce/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow carrots (rhs.org.uk/vegetables/carrots/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow leeks (rhs.org.uk/vegetables/leeks/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow cabbages (rhs.org.uk/vegetables/cabbages/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow French beans (rhs.org.uk/vegetables/french-beans/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow strawberries (rhs.org.uk/fruit/strawberries/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow sweetcorn (rhs.org.uk/vegetables/sweetcorn/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow lavender (rhs.org.uk/plants/lavender/growing-guide)
- RHS (Royal Horticultural Society) : How to grow rosemary (rhs.org.uk/herbs/rosemary/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow thyme (rhs.org.uk/herbs/thyme/grow-your-own)