Many people assume that as soon as their plants start to fade in the fall, it’s time to get to work pruning! This, however, is a common misconception. Although the weather is nice and we’d all like to get outside and “winterize” our plants, pruning is best left until the dead of winter. The good news? Here in sunny Southern San Diego, winter won’t mean much but a little more rain and maybe an extra sweater or two.
So why wait to prune your plants?
Probably the best reason is because most people don’t know what they’re doing! And we don’t mean that to sound snobbish – even experienced gardeners have trouble remembering which kinds of plants bloom on new wood and which on old, and even though there are rules of thumb, there are always exceptions. So better safe than sorry. Wouldn’t it be terrible to prune all of your azaleas, hoping for big, beautiful blooms in the spring time, only to find out you inadvertently removed all the buds? Which brings us to reason two…
Many spring-flowering plants put out buds towards the end of summer. This includes azaleas, camellias, forsythia, magnolia, dogwood and all flowering fruit trees like apples, peaches and pears. If you’re tempted to prune these plants during their deciduous period – which is tempting, we know – you’re going to remove a lot of the buds that have already formed, and therefore reduce flower and fruit production the following spring. It can also often be hard to tell which plants have buds, as some are very small or beneath the branch’s surface, so unless you know for sure your plant hasn’t already set buds, it’s probably a good idea to leave well enough alone.
Keep in mind that, during the fall, plants are trying to go to sleep for the winter. Pruning stimulates more growth – you don’t want to encourage plants to send out tender new shoots and leaves right before the temperatures drop. This is especially true of climbers and rangy plants like vines. Cutting them now will only result in rapid growth that will not survive the winter, ultimately leading to trauma of the entire plant.
What’s more, pruning plants like maples, birch, grapes and hardy kiwis – those that produce lots of sap – will cause them to lose precious fluids that they need to store up for the winter. Don’t leach them of these vital nutrients right before the cold months start.
So, when should you prune your plants?
Well, that depends. In general, although it seems counter-intuitive, it’s best to prune plants during or right after their peak bloom. They will be full of nutrients and, as it will be the spring or summer, they will put on vigorous new growth which will have time to harden off before the winter.
Otherwise, wait until the middle of winter, when plants are all ready completely dormant, before pruning. Plants in this stage are like patients under anaesthesia – they won’t feel a thing, they won’ t lose any sap and they certainly won’t try to put on new growth.
The only kind of pruning you should do in fall is to remove dead or diseased portions of a plant that were not visible when the plant was leafed out. You can gently clean up herbaceous perennials and ornamental grasses by removing dead leaves, but if it looks like it will be a particularly cold winter, leaving this dead material acts as a natural protective layer for the plants, and will serve to protect them even if you choose not to add additional mulch.