Well covered ground
No they do not conserve water, on the contrary they dehydrate the ground
But I do hedge my bets on this one!
P.K.Willmott was one of the greatest influences on my gardening philosophy. He was Head Of Horticulture at Askham Bryan College and was a great horticultural educationalist, universally known as PKW or, even more affectionally, just PK. He had two missions. One was to promote the voice of horticulture to Government and he worked for decades through the Horticultural Education Association (now the Institute of Horticulture) to improve the standing and image of professional horticulture. His other passion was to elevate the quality of advice given to amateur gardeners. He despaired of the incorrect information peddled in the gardening press. Sadly, he failed on both scores. Plus ca change and in both respects, things are worse now!
In his soil management lectures, PK would tell students how plants dehydrated the ground and how roots would grow deep to find water which would then be lost through transpiring leaves. He would contrast this with bare soil free of all vegetation. As bare soil starts to dry out, it quickly becomes self-mulching and surface evaporation stops. He did, of course, explain that the evaporative loss from initially wet soil is not insubstantial and each time a soil is rewetted by rain, evaporation starts again. Nevertheless, through the life of a crop, much more water is lost by transpiration than by direct evaporation from the soil. If an undisturbed soil is devoid of vegetation more water is conserved than if the soil carries a crop or grows weeds.
When the students went to do their practical with Head Gardener ‘Chalky White’, he would take them to look at the ground cover in the ornamental borders. He would lift the foliage and show them the moist surface soil. He would tell them, “the old man is wrong!”
Examples of situations where plants dehydrate the ground
- Most gardeners will have experienced for themselves extremely dry soil when lifting established plants, much drier than surrounding un-cropped soil. I frequently find this in spring when lifting early potatoes.
- I remember one year at Askham Bryan when the bedded wallflowers were lifted after a dry spring in late May. The soil was bone-dry down to about two foot deep and should have been heavily watered before the summer bedding was planted. It wasn’t and that dry summer the plants hardly grew at all!
- Lawns are one of the very worst competitors for water. Water loss is all the greater because mowing promotes active new green growth of grass. Gardeners frequently find that trees planted directly into lawns fail to grow.
- Luxuriant plants in pots, tubs and planters need frequent watering and yet plants with little foliage in adjacent containers die from overwatering when given the same amount.
- A gardener with a very weedy plot justified himself that he had left the weeds to conserve water. He was completely wrong.
My Acer griseum has grass right up to its base. It has hardly grown in ten years. Is it an example of my own incompetence or just inspired design?
But did Chalky White have a point?
Undoubtedly moisture lingers longer at the immediate soil surface when a canopy of leaves shades the soil and shelters it from wind. Although plants dehydrate the overall soil profile this moisture might be significant for germinating seeds and for wildlife activity. Also, when drought conditions prevail some plants have adaptations to reduce water loss. Might this have some significance? Plants do have amazing effects on soil ecology.
Has this self sown hellebore been able to establish despite or because of, aggressive Lamium galeobdolon?
Something we can all agree
- Plants are good for the soil!
- Ground cover is a beautiful and essential part of the ornamental garden. Far better to look at plants than bare soil.
All this vegetation will dehydrate the ground
…..previously in my myths series