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Soil Types: Clay Soils & Top 10 AGM Plants for Clay Soils

“Heavy soils,” or soils with a lot of fine clay particles, are difficult to manage but can be very fertile if treated correctly.

Spade in clay soil
Spade in clay soil

Quick Facts

  • Clay soils are composed of more than 30% fine clay particles.
  • Clay soils swell and shrink as they wet and dry, effectively cultivating themselves.
  • Clay soils take longer to warm up in the spring.
  • When dug into or walked on, wet clay soils are easily damaged.

Identifying Clay Soils

Clay soils are distinguished by:

  • Clays are dense and slightly sticky.
  • When a piece is rubbed between the fingers and thumb, it feels smooth and not rough.
  • Without cracking, a moist fragment can be rolled into a ball and shaped into a sausage.
  • It is likely that the soil is particularly rich in clay and is referred to as a “heavy clay” if the moist surface becomes shiny when rubbed after it has been rolled into a clay sausage.

Gardening With Clay Soils

Clay soils are:

  • Hard to cultivate and dig with
  • After a rain, slowly drain.
  • Warming up slowly as summer approaches causes plant growth to be slowed and makes it less “workable.”
  • However, in contrast to this, they hold water well.
  • Tend to be high in plant nutrients.

Warning: They lose their structure and become puddled and compacted if worked on or walked on while wet. This needs to be fixed quickly and thoroughly; As a result, damage should not be done at any cost.

Tips and tricks for gardening in clay soil:

  • When it’s relatively dry, dig in the fall and early winter. Clay soils, once soaked by winter rains, typically cannot be worked or walked on until the middle of spring.
  • Allow clay to be broken down by winter frosts.
  • When digging is necessary in wet areas, it is common practice to dig clay into narrow ridges to allow for more frost activity and better drainage.
  • Between waterlogged soils after the winter and baked, hard clay in the late spring, clay soils are frequently only workable for a short time.
  • Avoid planting or sowing too soon unless raised beds can improve drainage or the ground has been covered with cloches or clear polythene sheets for at least six weeks to dry and warm up ahead of time.
  • On clay soils, it is easier to grow climbers, many bulbs, trees (especially roses), shrubs, and other plants than it is for plants that need to be sown, planted, or divided frequently; such as annuals or bedding plants
  • Waterlogging can cause root damage if woody plants are planted on small mounds (25 cm/10 in).
  • The best time to plant trees, shrubs, and climbers is in the early fall, when the soil is dry and workable.
  • Maincrop vegetables typically have high yields and the potential to be of exceptional quality, despite the fact that early vegetables can be difficult to grow in clay soils.
  • Most tree fruits do well in clay soil, but some soft fruits, like raspberries and strawberries, have more trouble in clay soil.
  • When lawns are laid on clay soils, ample paths and stepping stones are typically required to prevent damaging wet clay soils from being trampled on.
  • In wet weather, lawns are frequently too wet to walk on for extended periods of time and are particularly susceptible to worm casts. To get around this, golf courses lay turf on a layer of sharp sand that is 7.5-15 cm (3-6 inches) thick. This method can also be used in gardens.

How To Improve Clay Soils

Clay soils can be improved in five ways:

  1. Create raised beds to prevent soil trampling and improve drainage.
  2. Consider a “no-dig” policy, especially for raised beds, which thrive in clay soils.
  3. Clay soils respond to more calcium, which causes the soil particles to flocculate—to clump together—in some but not all cases. Lime can be used where the soil is acidic, but gypsum is better elsewhere. The active ingredient in many commercial “clay improvers” is gypsum. First, test it on a small area to make sure it works on your kind of clay.
  4. Put in a lot of bulky organic matter, like manure or, better yet, composted bark, as this can significantly improve clay’s working properties.
  5. Applying organic mulch around trees, shrubs, and other permanent plants will help conserve moisture and reduce summer cracking.

Clay soils can have grit, sand, or gravel added:

In a soil, clay particles have a remarkable dominance. The different sizes of the soil’s clay, sand, and silt particles can help explain this. Although clay particles are extremely small, their large surface area dominates the physical properties of soil and makes it possible for more particles to fit in any given space, such as a 1 cm cube. Sand and silt, on the other hand, have larger particles, so it takes fewer of them to fill a space (say, 1 cm cubed again). Sand and silt have a smaller overall surface area, so their influence on soil characteristics is significantly less than that of clay particles.

In practice, this translates to: It takes a lot of grit or other material to reduce the amount of clay in a heavy soil. This is rarely possible except on a small scale, and the majority of gardeners prefer more practical options like raised beds, adding organic matter, and selecting plants that thrive in clays.

To make the soil easy to work, the proportion of clay in the top cultivated part of the soil would have to be reduced by half, even if a clay soil contained 40% clay particles—a relatively low percentage in comparison to heavy clay soils. The amount of grit or gravel required for this would be 250 kg per sq m (460 lbs per sq yd). When materials are added to clay, it can make the clay less stable and make the soil more difficult to manage. It is recommended to begin with small-scale experiments to ensure that any additions are worthwhile and will not adversely affect the soil’s workability.

Top 10 AGM Plants For Clay Soils

  1. Acer e.g.: Acer palmatum Sango Kaku
  2. Hibiscus e.g.: Hibiscus syriacus William R. Smith
  3. Fuchsia e.g.: Fuchsia Dollar Princess
  4. Hydrangea e.g.: Hydrangea petiolaris
  5. Allium e.g.: Allium sphaerocephalon
  6. Narcissus e.g.: Narcissus February Gold
  7. Cyclamen e.g.: Cyclamen hederifolium album 
  8. Hosta e.g.:Hosta ‘Sum and Substance’
  9. Helleborus e.g.: Helleborus argutifolius
  10. Roses e.g.: Rose Nostalgie

Specific planting conditions may vary for items in these categories. We recommend researching planting conditions for each plant before purchasing.

Frequently Asked Questions

What is clay soil best for?

“Because they securely ensnare roots in the soil, clay soils make excellent foundations for plants. Because their roots can get a firm grip on the soil, many annuals and perennials thrive in clay soils. They are able to withstand extremes of temperature and moisture with this firm grip, something that plants grown in sandy soil cannot do,” says Chris Bonnett, gardening expert for The Express.

Updated on November 16, 2023

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