Blueberries have acquired something of super-hero status in recent years. They’re vaunted as cancer-busting because of their high anthocyanin content, while research showed that blueberry extract reduced the effects of ageing on animals’ brains. Could it get much better?
Other fruits have similar properties, so don’t rush out and grub up half the fruit patch. Nor are they the only reason to grow blueberries (see our article Why You Need Blueberries which also details the different types that can be grown and the soil requirements), but they’re certainly a good reason why you should persuade your bushes to fruit as well as possible. This, of course, means pruning.
Understanding Blueberry Fruit Production
A blueberry bush grows canes which then produce branches and side-shoots. The fruit is produced on the tips of side-shoots which were new the previous year. (In essence, fruit is produced on year-old wood.) The most productive canes are around three years old. Wood that is over four years old begins to lose vigour and eventually becomes unproductive.
Why Prune Blueberries?
As old wood doesn't bear much fruit we need to prune it out to encourage new wood to replace it. A really hard prune will produce a flush of new growth and, with this in mind, some people prune only every three years but cut back a lot. This sort of thing never works for me, mainly because three years passes in a flash and, before you know it, five years have gone by and you have to start a rescue mission.
It’s easier to keep a bush consistently productive by cutting back every year. Some blueberries have a tendency to overfruit (give extremely heavy harvests) which can lead to biennial bearing, where you only get a crop every other year. Pruning out older canes will take away some of the fruit-bearing branches, helping keep the balance between fruit production and new growth.
Pruning also improves fruit quality, as removing some of the fruit buds will result in larger fruit.
Finally, of course, you want to keep the bush at a manageable height and its centre uncongested (to encourage air circulation, help prevent disease and let the sunlight penetrate to sweeten the fruit).
When to Prune Blueberries
In the northern hemisphere blueberries can be pruned at any time from November until March. However, it’s generally better to leave it until temperatures are warmer, around March in my garden.
Pruning in March also means that it’s easier to distinguish flower buds (fatter and rounder) from leaf buds (thinner and pointier), although you can wait until the blossom’s out to remove some, should you decide to do that.
Pruning Young Blueberry Plants
For a couple of years after planting, you really only need to keep an eye out for diseased, damaged or ill-placed branches and remove those. However, if you find that your young plant hasn’t bushed out in the first year, you could encourage it by cutting the longest stems back by around a third, to just above an outward-facing bud.
You will also want to remove all of the fruit buds in the first couple of years (yes, I know, it’s painful), and only allow a light harvest in the third, so that the bush puts its energy into growing.
Pruning an Older Blueberry Bush
The tidy-up comes first. Prune out all the dead, diseased wood. Remove crossing stems and any crossing or particularly spindly-looking branches. Then remove any low branches that will touch the ground when fruit-laden.
Blueberries have a shallow, spreading root system and suckers can sprout up some distance from the bush. Remove these to prevent the bush becoming too spread out.
Take away any accumulation of twiggy wood at the end of branches. Cut these back to an upward-facing bud or the nearest branch. If some canes are too tall for you, then head them back to an outward-facing branch.
Pruning Blueberries for New Growth
Now you want to prune for renewal, taking out older canes to encourage new ones. A good rule of thumb would be to ensure that you don’t leave in any canes more than six years old, and that a mature bush has one or two canes from each year below that.
So take out the oldest canes, either at ground level, or by cutting back to a vigorous-looking young side-shoot. (Old wood is grey, has spindlier side-shoots and fewer fruit buds.)
If, by any chance, the bush has thrown up a plethora of new canes the previous summer, remove all but a couple, choosing the strongest. If there’s little choice and a young cane looks weak, either take it out entirely or cut it back to a more vigorous side branch. Alternatively, if there are no new canes, you need to bite the bullet and prune back a bit more than you have before.
Should You Remove Fruit Buds?
A great deal of advice recommends removing fruit buds. This feels scary and I’d say get to know your bush and your own wants. Fewer fruit mean bigger berries, but you might prefer smaller ones. The pruning regime above may remove enough of the fruit buds to ensure that it doesn’t overbear, but if it blooms extensively one year and not the next, even with pruning, then you need to remove some of the fruit buds the following year and probably every year to keep it fruiting annually.
Pruning is an art, not a science, as I like to remind myself when getting panicked in front of non-textbook pruning problems. We don’t have to be perfect every time. Bushes don’t always perform according to the book, so get to know them, and if you find an older cane produces better than a younger one, teach the latter a lesson and remove that instead!
By Helen Gazeley