Monday 21 January 2019

A wet weather warning for your soil

As winter turns to spring, Gerry Daly has some advice for dealing with wet ground

Keep off the grass
Keep off the grass


With so much rain in recent months, the soil is squelching wet in most gardens, especially those with heavy clay soil. It is important to stay off garden soil when it is wet because the result can be damaging compaction. When that happens, the soil particles are squeezed together, destroying the natural crumb structure of the soil. This structure has been compared to a good fruit cake, the crumbs with spaces between them.

The crumb structure of good soil is about half solid material, one-quarter water and one-quarter air. Saturated soil might have no air. The soil pores allow vital air to reach the roots, and allow rainwater to percolate down and drain away. Roots of plants need air to survive and make new growth. Deprived of air, the roots of most plants die in a matter of weeks or even days.

Walking on soil that has drained is fine, because the porous structure can take the weight, but when the soil is saturated, the soil particles are lubricated by the water and they collapse easily. Walking the same track across a lawn or flower bed in wet weather will soon cause compaction.

When the crumb structure collapses, the pores are crushed and they cannot allow normal drainage to take place. Impeded drainage in areas of a piece of ground causes puddles of water to form in the low-lying parts, because surface water cannot drain away and it flows to the lowest point. Where water lies for more than a few days, apart from the damage to plant roots, other living organisms that need air can be killed, such as earthworms, beneficial fungi and bacteria.

The problems caused by compaction are more severe on heavy clay soil because its crumb structure collapses more easily and can take longer to recover. Light soil that contains more sand doesn't collapse as badly because the sand particles hold together and maintain the structure of the soil. This is the reason that golf as a sport began on sandy seaside links and why most golf greens are now sand-based.

The worst time for soil compaction is mid-winter to mid-spring when the soil is most likely to be full of water. Sometimes water only takes a few days, or should only take a few days, to drain away and it is then OK to walk over the ground.

On heavy soil, it is a good idea when planting to lay planks on the clay soil to spread the load and reduce compaction. If the soil is very wet, the use of machinery, even a wheelbarrow, should be avoided until the soil drains properly.

Prune rose bushes

n The old advice about pruning roses in March has changed - shifting weather patterns mean that the growing season now starts earlier. Prune rose bushes at any time between November and January for earlier flowering.

Stuck indoors?

n Can't get out to the garden because of all the wind and rain? Browsing the seed catalogues is a way of doing a bit of indoor gardening. Check out Brown Envelope Seeds, Irish Seed Savers for quality Irish-grown seeds.

Palm House

n When it's chilly and unpleasant outdoors, the Palm House at the National Botanic Gardens, Dublin, is comfortably warm all year round. Not only that, but it is packed with exotic tropical plants - the latest plant fad - and it is free to enter.

Sunday Independent

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