Chalky soil
A light, crumbly soil, pleasant to work, that needs regular inputs of organic matter to stay alive.
Simple definition
Chalky soil contains a high proportion of active lime (calcium carbonate). It is alkaline (pH > 7), often shallow, and organic matter breaks down very fast in it. It is easy to work but can block the availability of certain elements (iron, manganese).
Visual and tactile appearance
Grey to whitish in colour, sometimes light beige. Crumbly, light, dotted with small white stones. When you pour a little vinegar on it, it fizzes (the lime reaction). It dries at the surface very quickly after rain.
Main properties
- Alkaline pH (7.1 or above according to the RHS) that hinders the uptake of iron and manganese.
- Organic matter that mineralises very fast: it must be added often.
- Often shallow, with chalky bedrock a short distance down.
- Good natural structure, few compaction problems.
Advantages in the garden
- Pleasant soil work, even in early spring.
- Ideal for Mediterranean aromatics and many fruit trees.
- No excess moisture: healthy roots, few fungal diseases.
- Quick warming in spring.
Limits & common problems
- Frequent iron chlorosis: yellow leaves with green veins.
- Shallow: taproots can hit the rock.
- Rapid summer drought if the layer of soil is thin.
- Some acid-loving plants (blueberry, rhododendron) impossible to grow.
Recommended improvements
- Add plenty of mature compost and manure each year, on the surface.
- Thick permanent mulch to slow mineralisation and keep the coolness.
- For plants sensitive to chlorosis: add iron chelate or oak-leaf compost.
- Build mounds or raised beds if the soil is too shallow.
- Deep-rooting green manures: alfalfa, sainfoin, sweet clover, which like lime.
- Avoid lime amendments (already alkaline); prefer compost and broadleaf RCW.
Suitable plants
- Cabbage
In chalky soil, clubroot, a disease that deforms the roots, is less of a threat than elsewhere.
- Garlic
It dislikes very acid soils (below pH 6) and appreciates soil that drains, as chalky soil often does.
- Onion
It prefers a pH of at least 6.5 and tolerates very alkaline soils.
- Leek
It tolerates a wide range of pH, up to very alkaline soils.
- Beetroot
It tolerates neutral to alkaline soils, and even slightly salty ones.
- Lavender
It prefers a poor, dry soil, including chalky and alkaline ones.
- Thyme
It prefers a light, dry, chalky soil.
- Rosemary
It likes stony, chalky soils, light and dry.
- Sage
It prefers a chalky soil, provided it is well drained.
- Hyssop
Like thyme, it thrives in a light, dry, chalky soil.
Plants to avoid or watch
- Potato
Common scab, which covers the tubers in crusty patches, is worse in alkaline soil, especially if the soil dries out while they form.
- Blueberry
It demands an acid soil, ideally pH 4.5 to 5.5: in chalky ground, grow it in a large pot of ericaceous compost, watered with rainwater.
- Raspberry
It prefers a slightly acid soil (pH 6 to 6.7) and dislikes shallow chalky ground.
- Apple tree
To watch: it tolerates a slightly alkaline soil, not a truly chalky one; on chalk, look out for chlorosis, a yellowing of the leaves between the veins.
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
Guilds suited to this soil
These small plant groupings work particularly well on this type of soil.
Central
Strawberry guild
An efficient small system for edges, containers and the base of fruit trees: fruit, natural protection and biodiversity around the strawberry.
Link with crop rotation
Heavy metals: caution
Rather protective behaviour: an alkaline pH (> 7) naturally reduces the bioavailability of many heavy metals (lead, cadmium, zinc), they stay fixed in the soil rather than being taken up by the roots. Caution nonetheless with arsenic, whose mobility paradoxically increases at alkaline pH. 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) : Chalky soils (rhs.org.uk/soil-composts-mulches/chalky-soils)
- 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 garlic (rhs.org.uk/vegetables/garlic/grow-your-own)
- Plants For A Future, « Allium cepa » (pfaf.org/user/Plant.aspx?LatinName=Allium+cepa)
- Plants For A Future, « Allium porrum » (pfaf.org/user/Plant.aspx?LatinName=Allium+porrum)
- Plants For A Future, « Beta vulgaris » (pfaf.org/user/Plant.aspx?LatinName=Beta+vulgaris)
- RHS (Royal Horticultural Society) : How to grow lavender (rhs.org.uk/plants/lavender/growing-guide)
- Plants For A Future, « Thymus vulgaris » (pfaf.org/user/Plant.aspx?LatinName=Thymus+vulgaris)
- Plants For A Future, « Rosmarinus officinalis » (pfaf.org/user/Plant.aspx?LatinName=Rosmarinus+officinalis)
- Plants For A Future, « Salvia officinalis » (pfaf.org/user/Plant.aspx?LatinName=Salvia+officinalis)
- Plants For A Future, « Hyssopus officinalis » (pfaf.org/user/Plant.aspx?LatinName=Hyssopus+officinalis)
- RHS (Royal Horticultural Society) : Potato scabs (rhs.org.uk/disease/potato-scabs)
- RHS (Royal Horticultural Society) : How to grow blueberries (rhs.org.uk/fruit/blueberries/grow-your-own)
- RHS (Royal Horticultural Society) : How to grow raspberries (rhs.org.uk/fruit/raspberries/grow-your-own)
- Plants For A Future, « Malus domestica » (pfaf.org/user/Plant.aspx?LatinName=Malus+domestica)