JARS v40n4 - Mulch Ado About Nothing or To Mulch Or Not Too Mulch Is That The Question?

Mulch Ado About Nothing or To Mulch Or Not Too Mulch Is That The Question?
Robert A. Murray, Colts Neck, New Jersey
Reprinted from the New York Chapter Newsletter

One of the first pieces of good advice that I can remember receiving about plants and gardening was to mulch generously. Much later another even better bit of advice was, do not use peat moss as a mulch.

It is accepted as a matter of faith that the use of mulch is purely good. But is it? As time goes on, the answer is harder and harder to decide. What was once simple and direct, becomes even more complex as new factors present themselves for consideration.

The next dose of wisdom concerning mulch that I remember getting was to wait until cold weather, until several real hard frosts, at least, before putting mulch around plants to protect them from winter. Cold and the evils of the freeze-thaw cycles tearing at the roots of shallow rooted plants demand the protection of mulch. But if applied too soon, mice, and perhaps other wildlife, will recognize the protection that is being provided and make it their winter home. They will appreciate the mulch so much that they will relieve you of any worries over your root systems. They will eat them.

I have a friend who was looking out his window, admiring his shrubbery one fine, cold, windy day in March. As he visualized the many flowers soon to come, one of his prized bushes suddenly ran across the street. The grateful mice in his mulch had eaten all the roots!

Mulch is a good insulator in the summer as well as the winter. Excessive heat and high soil temperature can be very detrimental to roots. When the soil temperature gets too high, growth stops. High soil temperatures can promote the growth of destructive fungi, unless of course the soil dries out. Either way, the plant suffers. Mulch to the rescue. It keeps the soil temperature from getting too hot during the day. It retains the warmth during the night to promote growth. Most importantly, it retains moisture in the soil.

Usually, when mulch is considered, it is assumed to be an organic material of some sort. When this is the case, and it usually is, mulch contributes another benefit. As it bio-degrades, it improves the soil.

What then is the question? Is there a question? I do not know the answer, but there are some other factors to consider.

A rather straight forward one is the advice about peat moss as a mulch. It is recommended from time to time by knowledgeable sources, but it is hard to understand why. When peat moss dries out it creates a thatch that is difficult to wet and which is almost impenetrable to water. Peat moss is a very poor mulch.

A point that is a little more difficult to unravel is the benefits of mulch in protecting shallow rooted evergreens from winter cold. It is a fact that an evergreen must have the moisture in its leaves replenished all winter, even in the coldest weather.

Perhaps, especially in the coldest weather, because that is when the air is the driest and has the greatest desiccating effect upon the leaves. The mulch keeps the soil in the root area from freezing and thus ensures that the roots can supply the required moisture to the leaves. This sounds very reasonable and perhaps it is.

But, what if the mulch encourages the roots to stay near the surface which then makes the plant that much more vulnerable to the soil's freezing? There are some students of hardiness (not very many, to be sure) who feel that this is the case. They are very cautious of using mulch. By allowing the soil temperature at the surface to rise and by allowing the surface to become dry, they hope to drive the roots deeper and thus decrease their vulnerability during the winter.

I have no data, but even if this works, it would seem that the plant growth would be less vigorous and might not be as attractive. On the other hand if you live where the temperatures go quite a bit below zero, and stay there for long periods, then it may be the only way the plant will survive, let alone be full lush in its growth.

I wonder also about petal blight. Would it be as great a problem with no mulch? With a dry soil surface, it might not have as favorable a condition for growth and multiplication.

The soil in our area is very sandy and it drains unbelievably fast. I do not think that rhododendrons and azaleas could be grown here without mulch, certainly not out in the open. Even in shade, I think there would be a problem.

Knowing this, when we were starting our garden, we were very enthusiastic in seeking sources of mulch. A friend had a grove of pine trees with a thick layer of needles which he considered to be somewhat untidy. When he decided to clean them up, it was our golden opportunity. We hauled the needles to our rhododendrons to give them a real treat, and that is how we acquired poison ivy.

If this has any point, I think it is that nothing is as simple as it seems. Take advice with some care, even from experts, and try not to go overboard with anything. Is that asking too mulch?