Like most garden writers, early on in my career I often repeated advice given by experienced experts on topics I didn’t know much about myself. Years later, there is quite a bit of advice I’d like to take back, for example this old song on pruning raspberries:
"Remove old canes after they have fruited by cutting them off at the soil line."
This sounds good, and I accepted the logic that the dying canes would harbor diseases, so we had better get them out of there. Fast forward a few years, during which I repeatedly tried and failed to follow my own advice. Crawling around on the ground with pruning shears hoping I cut the right canes, and then pulling out the thorny things was hazardous duty, for me and the new green canes that would bear next year’s raspberry crop.
Pruning Summer-fruiting Raspberries
My raspberry pruning was doing more harm than good and I was having no fun at all, so I changed my ways and started waiting until winter to lop out the old canes, which had gone gray with age so they were easy to spot. Winter revealed another hidden truth: The old canes provide support for the new ones, so pulling them out in summer deprives the plants of their fundamental growth habit. Meanwhile, horticulturalists began suggesting that dying bramble canes send leftover carbohydrates back to the roots, and you wouldn’t want to shortcut that process. The new advice for pruning raspberries goes like this:
"Remove old canes in late winter by cutting them into pieces with pruning loppers."
My next mistake was leaving out something important – thinning the new canes when they come up in spring. The new canes are growing with a vengeance by the time you are picking raspberries, and there are usually too many of them. Pulling out about a third of the new canes – especially the earliest ones – keeps fresh air circulating around the ripening raspberries, and invites the canes that are allowed to grow to become husky and cold-hardy.
Speaking of cold, the next bit of advice I need to recall is this:
"Wait until early spring to tip-prune raspberries, because until then you do not know the extent of winter injury to the canes."
At the time I wrote this, I had not yet met black raspberries (Rubus occidentalis) or the purple strains created by crossing them with red raspberries (for example, the ‘Royalty’ and ‘Brandywine’ varieties). These big, vigorous brambles will only grow into heavy-bearing bushes if they are tip-pruned in summer by cutting off tips of the new canes when they are about head high. Pruning raspberries this way forces secondary or lateral branches to grow from nodes along the stem. In my experience, the berries from these lateral branches are bigger and easier to pick than those from plants that receive no discipline until spring. Sometimes winter cold nips them back, but some winter injury is to be expected when winter temperatures drop below about -5°F (-20°C).
Pruning Fall-Bearing Raspberries
As for tip-pruning fall-bearing raspberries, I think each gardener must come to an understanding with the variety under their care. Ideally, you want the berries to ripen while the weather is still warm, because warm sunshine makes raspberries taste better, but you don’t want them coming in so early that the fruit gets scalded by summer sun.
Pinching the new canes at eye level delays fruiting of fall-bearing raspberries by about three weeks and forces the development of lateral branches, so it is a very sound practice in warm climates where you want raspberries to wait out the hottest part of summer before they bloom and set fruit. But in cool climates where you want fall raspberries as quickly as possible, it is best to leave the terminal buds intact.
Home Grown Raspberry Leaf Tea
All of this raspberry pruning can net you a garden crop I’ve failed to cover in previous writings, which is raspberry leaf tea. Raspberry leaves contain more tannins than other common tea herbs, so they add body to herb teas made of mixed, dried herbs from the garden.
By itself, raspberry leaf tea is widely recommended as a tonic for severe menstrual cramps or even the pain of childbirth. There are no widely accepted studies to back this up, but the health industry is generally not interested in helping people grow drugs in their back yards. I like the flavor of raspberry leaf tea, but if you don’t you can always put it on your face. Some cosmetics researchers think a little raspberry leaf extract added to skin creams might prevent help wrinkles.