June is the ideal time to examine your fruit trees and assess their fruit-set – the volume of blossom that has been pollinated and is forming fruitlets – and then decide on how many of them are in need of thinning out.
Thinning out – removing a number of fruitlets from the tree by hand, with scissors or secateurs – is an operation that’s essential for both the quality of the fruit you’ll be harvesting later in the year, and the health and longevity of the tree.
In later posts I’ll be talking in much more detail about the research into thinning that I’ve been reading up on. For now, here’s a quick ‘why and how-to’ guide, with photos from the thinning work that I carried out on the Plot #79 orchard last Sunday afternoon.
Why You Should Thin Out Fruitlets
In a much-condensed form, the main reasons for removing a proportion of each tree’s fruitlets are:
Avoid Unnecessary Damage
The sheer mass of un-thinned fruitlets puts a lot of strain on a tree’s branches, especially if the tree is a relatively young one, with thin branches with wood that isn’t all that strong. Branches will naturally bend under the weight of fruits as they develop – it isn’t a problem per se – but if they bend to breaking point then it can become a problem for the tree.
A broken branch could drop down through a tree canopy, causing more damage as it falls. Or it could tear away from its parent branch or trunk, leaving a large, open wound that could become an entry point for tree diseases, such as apple canker.
Thinning fruit reduces the overall load on branches and hopefully helps prevent this sort of damage.
Better Quality Fruit This Year
The more fruits left on the tree all summer, the more widely stretched the tree’s resources will be and the smaller and less sweet the fruits will be on harvest in Autumn.
Massively over-simplified version: if 100% of the tree’s available resources – the outputs from photosynthesis, mainly carbohydrate (sugar and starch) compounds – are divided between 100 fruitlets, then each one receives 1% of the resources. If the number of fruitlets are reduced to 50 then each one receives 2% of the resources, and can potentially grow twice as strongly. Reduce them to 25 and the growth potential doubles again.
In reality the situation is far more complex, but all studies into thinning have shown that removing a proportion of the fruit improves the quality of the remaining fruit on harvest, compared to un-thinned control trees.
More Fruit Next Year
Not many amateur growers are aware that next year’s fruit buds are already forming right now, whilst this year’s fruits are growing and ripening on the trees. Apple and Pear buds develop and differentiate into potential fruiting buds over the warm, sunny months of summer and then go into dormancy over the winter. Then, if conditions are right next spring, they break dormancy, fully differentiate into fruiting buds and produce blossom.
Again, it’s a question of the division of the tree’s resources. If a tree is producing a lot of fruit then the majority of its resources will go into attempting to grow and ripen the fruit (or more specifically, the seeds inside the fruit), leaving fewer resources for the development of next year’s potential fruit buds.
At worst, this can result in the tree adopting a ‘biennial bearing’ pattern, following an overly-fertile year in which it produces masses of fruitlets, with a barren year in which it produces hardly any, or none at all. If allowed to continue, this can become a regular cycle of boom and bust, bumper harvest and exhausted rest.
Thinning out fruitlets helps to balance the division of resources between this season’s fruit production and next season’s potential fruit production, which is generally better for us, as growers, who would prefer a steady supply of fruit every year.
When To Thin Out Fruitlets
The timing of fruit thinning will and should vary, depending on local conditions – which part of the country you’re in, the specific topography and situation of the orchard – and recent weather patterns. As a general rule-of-thumb though, I tend to wait for evidence of the ‘June-drop’ – when trees naturally shed a proportion of fruitlets that haven’t taken well – and take that as my cue.
How to Thin Out Fruitlets
Not every tree is easy, or even possible, to thin out, and not every tree requires thinning. The larger a tree is, the less likely you are to be able to reach the fruit clusters safely or easily. What you can do in that case is give the tree (if it’s not to massive), or as many individual branches as is feasibkle, a gentle shake to dislodge any loosely-attached fruitlets and help the June-drop along. Beyond that, try to thin out as many of the lower-positioned fruitlet clusters as you have time for, and then you’ll just have to let nature take its course in the inaccessible parts of the tree.
Smaller trees, and particularly young, recently-planted trees should be thoroughly hand-thinned if required. We have 16 three-year-old apple and pear trees in the Plot #79 orchard, and I hand-thinned the 14 that are bearing fruit this year in just under and hour and a half, so it shouldn’t be too lengthy or laborious a job.
The process itself is relatively straightforward. Examine the fruitlets on a cluster-by-cluster basis. For each one, decide whether it is bearing too many fruitlets and, if so, which one(s) need to be removed. You should ideally be keeping just one fruitlet per cluster. Two if it’s the only cluster on a branch, or other clusters are spaced out well. None at all if there are other clusters very close by – which can be common on spur-fruiting trees – that have stronger fruitlets.
Start with any fruitlets that are obviously damaged, miss-shapen or under-sized and snip them off, cutting the stalk as close to the point of origin (where it joins the stem) as you can without risking damage to the fruitlets you want to keep. Don’t forget to gather up all the fallen fruitlets for the compost bin, to avoid attracting slugs and snails.
The same principles apply to pears as well as apples, although pears are less likely to form densely-packed clusters of fruitlets. They’ll still benefit from being thinned out where pairs of them are growing too closely together.
Here are a few examples from last Sunday’s thinning session to give you a few pointers. The cultivar is ‘Lord Clyde’, a mid-season (October) cooking apple (that was raised around 1866, in Stockport).
This cluster has four well-formed fruitlets and one – in the center – that has failed to pollinate. I decided to leave two fruitlets here, because it was the only cluster on the branch and so wasn’t likely to be competing for resources with many others. You can see some slight damage to the fruitlet on the right, which was removed, and that decision then dictated which other fruitlet I needed to remove, based on allowing the best spacing between the two remaining. This is a cooking apple, after all, so each fruit has the potential to grow quite large if it’s given enough space to grow into.
Here we can see a cluster of clusters; many fruitlets crowding together on a fruiting spur network, all coming off a single branch. I removed most of the smallest fruitlets, leaving just one fruit per spur.
Here we have another tightly-packed cluster of small fruitlets, with another two clusters in the background. As I started checking the fruitlets a few of them dropped off under very little pressure, suggesting they weren’t at all well-formed, and in the end I decided to remove all the fruitlets from the main cluster. One fruitlet was left on each of a pair of clusters slightly further down the same branch (you can just see them in the background).
By the time I’d repeated the process for the whole tree, I’d cut off a fair number of fruitlets:
It might look a bit drastic, but remember the dual goal: to improve the quality of the remaining fruits as they develop, and to improve the chances of repeat-blossoming next year, rather than a barren rest-year.
Of course, there are no guarantees. The remaining fruits could be affected by drought over the summer, torn loose by high winds, or damaged by apple scab, codling moth, pigeons or other pests. But thinning should also help to lessen the danger of infection or infestation, by increasing the air-flow around the fruits, and allow them to grow and strengthen against attack.
Likewise, poor spring weather could prevent blossom-set and pollination next year. But at least thinning this year will free up the tree’s resources to establish potential fruit buds in the first place. If they remain dormant for another season, then that’s just how it sometimes goes.
If you have any questions, queries (or corrections of the above) please feel free to post them via the comments and I’ll get back to you as soon as I’m able to.