At the time of writing, the end of October, the shade temperature is still about 28 centigrade. I could be forgiven for thinking that winter is ages away, but in gardening terms, this could be a costly mistake, despite living in a relatively mild winter climate. I live, work and garden in central Israel. In some areas the winter lows reach about -2 c. in others, frosts are very rare. If like me, you live in a dry Mediterranean climate, typified by mild wet winters, then it would be prudent to be aware of the effects that pruning at this time of year can have on the garden plants, and particularly on the most precious object in the garden – the tree.
Before going into that though, let’s discuss briefly some reasons for pruning in or around the autumn. The fall is actually a mini growth season in Mediterranean climates. With the drop in temperatures, rise in humidity, and shorter days, plants tend to enjoy a brief period of resurgent growth after the torrid heat of the summer. It can be worthwhile taking advantage of this, to encourage compact growth in landscape bushes, which can be effected by light pruning and clipping. The same is true of many herbaceous flowering perennials, whose flowers have withered, and look somewhat lank and “leggy”. Some ornamental grasses tend to look extremely poor as winter approaches, while pruning them down, encourages new growth before the low temperatures curtail further growth until the spring.
There is no problem in pruning cold hardy plants in the winter, but cold sensitive species are liable to be damaged, sometimes fatally so, by being cut during the cold season, or in proximity to it. To be safe, cold sensitive plants should not be touched from about six to eight weeks before the possibility of frost or chilly temperatures. The reason is that wounds to non-hardy plants caused by pruning cuts, are highly likely to be the source of bacterial or fungal infection and to increase the plants’ susceptibility to the cold. So if your still basking in the glow of the autumn sun – BEWARE!
When it comes to naturally deciduous plants, which are generally cold hardy in any case, light pruning is fine, although the heavy seasonal tree pruning, or the pruning of rose bushes and Crape Myrtles, should be carried out during the dormant season. In mild winter climates, it’s important to delay this type of pruning until the later half of the dormant season, and not in the middle of the winter as in continental Europe or North America. This will be the subject of a future article.
So how are you to know which plants are liable to be cold sensitive, and which ones are hardy? Obviously it helps to know the precise botanical names of your garden plants, and to check up their hardiness in literature or on the net. Here are some general guidelines though which you may find useful.
Evergreens, excluding coniferous plants, vary in their sensitivity, but are never hardy to temperatures below say -6 or -7c.Examples like Olive trees, Carob and various species of Lantana come to mind. When in doubt, assume that an evergreen specimen is sensitive and do not prune until every possibility of frost has passed in the following spring.
Plants that drop their leaves in the winter, may not be naturally deciduous, but may in fact be of tropical or sub-tropical origin, and the leaf drop occurs in reaction to the relative cold to which the plant is exposed to during the winter. Here lies a potentially nasty trap, because species in this category, like Duranta or Lantana for instance, can be highly marginal for your area in the best of circumstances. These types must never be touched until the spring. On the other hand, and this where things can get a bit complicated, the worst time to heavily prune the real deciduous plants is during the spring, as the sap rises through the wood after the winter dormancy has elapsed. So before rushing in to prune bare leaved trees and shrubs, find out exactly what you are pruning!