Growing Things: How a rockery can help you grow in heavy clay soil

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One question that I am often asked is ‘What can I grow in very heavy clay soil?’ The answer invariably is not very much unless you are prepared to invest a lot of time, money and effort into adding and working in organic matter into the soil.

One job stands out from my time as a landscape contractor when it comes to clay soil.

The home we were working on had not only clay but a lot of rock as well. It was a very difficult area to plant in. A pickaxe was about the only way to make any type of a hole in this conglomeration of clay and rock and yet the homeowner wanted a showpiece landscape feature right in the middle of the worst of the clay.

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My idea was to create a rock garden on the spot in question. The reasoning behind this was that by adding soil on top of the clay and rock we could create a planting area where small or shallow rooted plants would be quite happy. The bonus was that we had access to a lot of rocks from previous excavations on the property. So we set about mounding good quality topsoil in the shape the homeowner wanted and then carefully placing the rocks into the mound of soil.

If you are considering building a rockery here are a few tips:

• Choose a good quality loam that has lots of organic matter in it. Using good quality soil in the beginning will avoid problems later on.

• Decide on the size of the rockery you want and mark it off with string or an eco-friendly paint marker. The size will be dictated by the type of rockery it will be.

• Will it grow dwarf or alpine plants or will you use it to grow annuals or perhaps shrubs?

• Pile the soil on the area. It should be piled to a minimum depth of 40 cm and can go as high as you like. Once the soil is in position, it is simply a matter of placing the rocks in the soil. Try to create pockets where plants can live. Also, try to make the rocks look as if nature had placed them. Partially burying them is the way to create a natural look.

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Choose plants that are right for the application. Look for alpine or rockery plants in the garden centre

A list of a few of my favourite rockery plants:

• Dwarf Columbine (Aquilegia flabellate ‘Nana’)

• Dwarf balsam fir

• Draba aizoides

• Alpine Dianthus

• Silene

• Saxifrage

Every week, Growing Things Outdoors runs online at or, if you prefer an epaper format,

Learn more by emailing your questions to [email protected], reading past columns or my book Just Ask Jerry. You can also follow me on Twitter @justaskjerry01.

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