Tips for gardening on chalk soil is here to help you if you have stony, chalky earth in your garden. It may be that you’ve recently moved house to a different area and are faced with chalk soil for the first time as a gardener. Or perhaps you’re new to gardening and are wondering how best to grow flowers, fruit and vegetables when the azalea you planted turned yellow and died!
Chalky Soil
Chalky soils are alkaline and free-draining, and the depth of soil over chalk varies considerably. Limestone soils have similar characteristics. Although theoretically, the soil could have a pH of 7.1 – 14, in the UK alkaline soils are unlikely to be naturally higher than pH 9.
Chalk gardens have soil which is alkaline, ie with a pH above 7. In the UK these are found in areas such as the South Downs, Chiltern Hills and Salisbury Plain. And in areas with limestone deposits, the Yorkshire Dales being a prime example, the soil is also likely to be alkaline.
Alkaline soils often have a whitish colour and often contain pieces of chalk, lime, flints. As well as carrying out a pH test, one of the minor experiments we sometimes carry out in Plews Gardening Courses is this. We get an empty jam jar and fill it a quarter to a third full with vinegar (white or ordinary malt, its not crucial which). Then we add a spoonful of chalky soil and watch it froth up! This is due to the release of carbon dioxide and can be a fun thing to do with your children too.
Gardening on Chalk Soil
Chalk soil may be light or heavy soil, depending on various factors such as how stony it is. By light or heavy, this refers partly to how workable or diggable the soil is.
Disadvantages
- Frequently stony
- Rapid drainage can lead to a dry soil, especially in warmer weather
- Minerals such as iron and manganese will quickly leach out of the soil if it is overly free draining
- The soil depth may be shallow
- Deep or sticky chalk soils can resemble clay soil; for example, cold to warm up, difficult to dig
- Chlorosis
Advantages
- Leaching of minerals can be remedied to an extent by regularly adding organic fertiliser
- Adding plenty of organic matter on a regular basis turns chalk gardens into fertile sites whether they are shallow or sticky
- Generally, chalk gardens have light soil, easy to dig at anytime of the year
Tips for Problems when Gardening on Chalk Soil
Compost and organic matter
Where there is sufficient soil depth, then the regular addition of organic matter is important. This may be compost made in the garden, or brought in.
Leaf mould can be particularly beneficial where a slight reduction in the soil pH is needed, although it is not a ‘quick fix’
Adding organic matter will improve the water retentive properties of the soil
Chlorosis
Chlorosis is where the mineral iron is locked up in the soil and therefore unavailable to the plants. This can happen even when lime tolerant plants are grown. The annual application of sequestered iron in the spring may be required if yellowing of foliage is observed.
Shallow alkaline soils
Where the soil depth is very shallow, there are three main options: –
Topsoil
Firstly importing large quantities of topsoil. Due to the cost (of both materials and labour, unless you do this bit yourself) this may only be an option for certain areas of the garden. Where new trees are to be brought in, it is worth considering as it is the quick method of gaining the requisite soil depth. And, as the topsoil can arrive with added nutrients, it also gets around the issue of low soil fertility.
Growing methods
Secondly, it may be worthwhile considering alternative methods of cultivation. For example, this could be by using the lasagne gardening technique, where after removing perennial weeds, layers of organic matter, cardboard, grass clippings etc are added to gradually deepen and improve the top layers of soil by the action of worms and decomposition.
This would be particularly useful in the kitchen garden, but it is a technique that can be used in ornamental borders too. See the blog link below for more on lasagne gardening.
Raised beds are another possibility, and would be neater and more suitable in formal areas of the garden. Topsoil may need to be brought in, so the cost of building the raised beds and fresh soil would both need to be factored in.
Breaking up larger pieces of chalk
Thirdly, breaking up the chalk to enable the plants to spread out their roots more easily and establish more quickly. This option will still require organic matter and / or top soil, but could be an option where small, young plants are being planted.
What to Grow when you’re Gardening on Chalk
You will be pleased to learn that there are many popular plants that naturally grow on chalky and limestone soils. On shallow soils, especially chalk gardens in coastal areas, consider the qualities that native plants have. This can lead to some exciting choices for the garden.
Generally speaking, chalky soils are best suited to plants that like sharp drainage and are not too greedy in terms of nutrient requirements. For example, Pinus mugo, the dwarf mountain pine is happy on a chalk soil and with salt air and could look delightful encircled by Lavender with Calendula adding a summer splash of contrasting colour.
Deeper chalk soils will give a wider range of plants, as the soil tends to be more moisture retentive even before the addition of organic matter. Although adding compost is always good for the soil, and should be a regular feature of your gardening year what ever soil you garden on.
The lists below are just to give a flavour of plants to grow when you’re gardening on chalk soil, there are plenty more: –
Trees
Arbutus unedo, the strawberry tree
Buxus and Yew – excellent for topiary and formal gardens
Flowering cherries
Gleditsia
Hawthorn
Tamarisk, particularly good for coastal chalk gardens
Flowering Shrubs
Buddleia
Ceanothus
Deutzia
Erysimum, perennial wallflower
Hydrangea
Oleander
Osmanthus x burkwoodii
Rosa rubiginosa
Syringa, lilac
Weigela
Climbers and wall shrubs
Akebia, chocolate vine
Clematis
Cotoneaster
Lonicera, honeysuckle, both summer and winter flowering varieties
Parthenocissus – Virginia creeper and Boston ivy
Herbaceous Perennials
Dianthus, cottage garden pinks
Doronicum
Erodium
Geranium
Hemerocallis
Hosta
Iberis sempervirens, candytuft – another coastal chalk garden stalwart
Miscanthus sinensis
Nepeta
Rudbeckia
Thalictrum
Bulbs, Corms, Tubers
Chionodoxa
Colchicum
Crocus
Annuals
Calendula
Cornflower
Sweet alyssum
Sweet peas
The Kitchen Garden
Phacelia is often grown as a green manure on chalk soils. It is also worthwhile letting some of the green manure crop flower as phacelia is excellent at attracting pollinators.
Clover is another good green manure crop for chalk gardens that can also help reduce soil erosion over the winter due to its extensive root system.
Vegetables
Brassicas in particular as the lime in an alkaline soil reduces the problems of clubroot, so for example –
Brussels sprouts
Cabbage
Cauliflower
Pak choi
Swiss chard
Most of the legume family (Fabaceae) prefer alkaline soils so peas and beans of all types will thrive. Growing these has the added advantage of fixing nitrogen in the soil which the next crop can take advantage of. This is particularly useful when using a crop rotation system in the vegetable garden.
Artichoke
Asparagus
Beans
Leeks
Mushrooms
Okra
Peas
Spinach
Sweetcorn
Fruit
Apple
Black Mulberry
Cherry
Kiwi
Pear
Herbs
Borage
Garlic
Lavender
Marjoram
Parsley
Rosemary
Peppermint
Thyme
Yarrow
Gardening on Chalk Soil
A chalk garden with a deep layer of alkaline clay soil would be a delight to garden in. The problems occur where the pH is particularly high and the soil depth is shallow. Although it will take time to get there or money to do it more quickly, it is worth it.
If you would like help with gardening on chalky soil, a garden design or planting design do get in touch. Plews is able to offer you a Garden Consultancy Visit, Gardening Lessons, Garden Design and Planting Design to suit your needs. Please check out relevant pages on the website for more details
For further gardening tips and inspiration check out Plews Potting Shed blogs, including the selection below – and find us on Instagram and Facebook
Related Gardening Blogs for You from the Award Winning Plews Potting Shed
Soil
Soil – the plant food in your garden
Lasagna Gardening – Growing Methods for Gardeners
Soil Preparation – Double Digging
What is the Point of a Raised Garden Bed in the Vegetable Garden?
Plants
Hawthorn
Buddleia – Butterfly Bush or Beast?
Hydrangea
5 Favourite Vegetables
The Garden Pea
Bramley Apple
Other gardening blogs of interest
Tips for Gardening on Clay Soil
Elements of a Formal garden
