I'll start by saying that most of the discussion here will apply to all fruit trees, but there are some minor variables I will try to address. It won't all apply to shrub fruits/berries and vines.
I am also going to try to keep the advice simple and straight forward. It can be a very daunting topic that seams to overwhelm everyone.
The perfect time to prune is while the trees are still dormant, so ideally late winter or early spring. It's good to try to get it done before the buds break, and sap starts really flowing as it will allow the tree to better divert it's energy. If you miss the perfect time, it's still better to do it late than never. In Northern Ontario the best time is generally around March or April.
The first main fundamental of pruning. You want to always get rid of any branches that are Diseased, Dead or Damaged. Watch out for this through the entire season and if you notice a branch that seams to be diseased, dead or damage, be sure to prune it right away, even if it's the middle of summer and active growing. Leaving these intact can significantly weaken the tree and allow bugs, pests and diseases to further invade/infect the tree.
I like to refer to it as "art" as there isn't really a "right and wrong" way to do this. It's not a scientific undertaking, it's a matter of preference and your desire for the tree. Following the advice below will help it produce more and better fruit that is easier to harvest, and prevent damage to the tree.
This is the first step I would focus on when pruning, is looking to have your trees establish the ideal form for fruit production. This step is more important for younger trees, lets say 1 to 4 year old trees. (If you've got them from us, we always prune them when they arrive to a desirable form to get started for the first year. but I'll describe how we select anyways)
This is also where people can really start getting overwhelmed and confused, often because there is lots of option and advice out there. Some people will suggest fancy training and techniques to get various shapes, we're not going to get into that and try to keep it basic.
To start you want your tree to have 4 to 6, strong and well placed main lateral branches around your tree. These are going to be main branches through the whole life of your tree. We try to select branches that are approx 90 degrees from each other around the truck and at least 1" to 2" apart. If you look straight down at your tree from the top, you want one branch at (12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock. I'll add a few photos below shortly of some younger and older trees. The other important thing about these branches you select is what they call "crotch angle", or the angle the branch grows from the tree. I would say the ideal is approx 60-80 degrees, but generally anything between 45-90 degrees is fine. I'll include a few more photos of this as well. These angles are ideal as they make good strong branches as they grow, if the angle is more narrow they can be weak pull away when the branches are heavy with fruit. They will also cause crowding of the trees. (This is where different trees have slightly different tendencies, pears and some varieties of apples and plums are very upright and it's hard to find these perfect branches, so you can actually "train" them to be more open when they are very young. You can use any sort of commercial or homemade limb spreaders or tie them to stakes in the ground. This isn't mandatory and can do more harm then good if done wrong, but I thought it was worth mentioning).
Once you've selected these main limbs for your trees, then cut all the other branches coming off the main truck. I know it sounds severe, but it's usually actually not that much cutting.
I don't always do a lot of trimming at the tips of the branches, but in the first few years, I can help to keep the tree more balanced. If one branch is getting way longer then the others try to balance their lengths. It's also good to cut them back if they are growing as high as the tip or competing with the "center leader" of the tree.
When it comes to trimming the top of the tree, we usually do cut them back annually to promote the growth to these main branches and keep the trees from getting to tall to fast. Of course this is also a matter of preference, if you want a really tall tree some can grow up to 40ft if you let them, but this is a huge problem when it comes to actually harvesting the fruit.
Once you do this branch selecting and training stage in the first few years, the ongoing years are mostly just maintenance.
If you tree is already much older, it's a bit harder and more delicate to reshape it, I won't talk much about that, but try not to remove more than 25% of the tree in a single year.
Once your trees are well shaped and growing your pruning changes slightly. You already have you main branches established and you mostly want to keep the tree clean, open and uncrowded. This will help it getting a good fruit crop but also prevent disease and keep he tree vigorous.
You'll want to remove all these from your trees and branches. These are very vigorous new growth that is usually going straight up. They take a lot of the trees energy and don't produce fruit, and would be unlikely to adequately support fruit if they did grow on them anyways.
The next thing I look for when pruning is growth that crosses each other and especially touches the other. They will rub and get damaged. They will also compete for light and resources.
Any of the sub branches on my main branches that are growing straight down, or below the main plane of the branch get's removed, it's going to be shaded and also very weak. Same with things growing above the branches, they are just going to shade below and be weak. You are looking for your branches to fan out nice and flat as they grow.
So that's mostly it, those are the main fundamentals of what your doing. Don't stop reading yet though, I'll touch a bit on the 'technical aspects of it"
This is nitty gritty how to part of the job. You can do everything above with just paint and plan or debate, without yet making a single cut.
This is first for a reason and I can't stress the sanitation part enough, make sure your clippers are clean, sharp and sterilized first. The last thing you want to do is pull them out of a pile of weeds in the garden shed and start cutting away, you can introduce all kinds of nasty stuff. This is also very important when your cutting any diseased branches off. You don't want to infect your whole orchard. The same also goes for removing the wood and cuttings, don't let them rot on the ground around your trees, they are a host for all kinds of undesirable things. If you do think they are diseased or have pests I would suggest honestly suggest burning them all right away, (you don't want to give this gift back to the forest). If you don't suspect any disease or pests your safe to discard of them anyway you otherwise would or see fit.
When is say "sterilize" your clippers I don't mean you need to buy an autoclave or anything that intense. Give them a good clean in hot soapy water. I do recommend wiping them between each different tree as well, you can use anything from diluted bleach or alcohol, vinegar or household cleaners or wipes. I've read just about every recommendation.
I'll just talk about basic clippers and not get into all the fancy different saws and stuff. Don't cheap out, get a good sturdy pair that is sharp and don't hesitate to replace them once they are not making a clean cut and leaving little frayed and ratty edges. They have to go, they are doing way more damage to the tree. Use bypass pruners, where the sharp edge that moves fully crosses a fixed but sharp alternate blade, these are the most common ones available. Avoid using "anvil" or "scissor" types. Usually a small hand held pair is fine and we're just taking off young new growth. If your working on an older tree and larger branches you will need larger other types and saws.
Can you believe you've read all these instruction and still haven't made a single cut yet, and in the introduction I said I'd keep this brief and simple.
The important part of making your cut is getting it in the right place, for most of the cutting described above your cutting a branch right off. In those cases you don't want to leave it too long or too short. Don't leave a stub when your cutting off a branch, it will just die back and allow pests and disease. Also don't cut it "perfectly flush", cut approx 1/8" inch from the stem at the branch collar. This is the small thicker overgrowth at the base of the branch. See the photos below.
If your just cutting off small branches there's generally no need to seal these cuts and they will heal fine. If you are removing very large branches you can cover them with pruning wax, try to avoid the fine paints and asphalt based tars.
If your cutting the central leader or trimming the branches you will want to pay attention to where the bud is. Cut approx 1/4" past the bud on a slight angle, instead of just a blunt cut. That bud will usually send out a new branch, so you can select a bud with a desired direction to help force the branch into a more open pattern this is especially helpful with pears and other "upright trees"
I know I already said this in the sanitize part but I want to say it again, be sure to clean up your cuttings and don't leave them hanging around to cause you other issues. They are also a tripping hazard and can mess up your lawn mower.
Simple right, or are you even more confused. I'm going to try to share lots of photos and some videos of the techniques as well.
We usually also offer a few onsite workshop and lessons each year, (which unfortunately won't happen due to COVID-19 at this time). It's certainly something we hope to do more of and look forward to further partnering with the community gardens and other local organizations so don't hesitate to reach out to us to organize something like that.
Unfortunately we don't currently offer any on site pruning or tree maintenance services. Thought I'd mention it as we usually get lots of requests.
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