I am about to undertake a serious summer pruning on my nectarine because... it needs it. Tree has grown too tall and I want to push out growth from lower on the tree, especially lower limbs that have grafts on them.

In many cases there may not be an exact right or a wrong about summer pruning, but rather whether it makes sense for your tree and what you want to accomplish.

Anytime growth is happening where I don't want it, I suppose it makes sense to nip it in the bud.

Where you are I fail to see why winter pruning should be forbidden. Rules without explanation are not helpful in understanding the subtleties of training and pruning. When in doubt, stick to a university site in a similar climate as your own. Even if they don't have explanations with their instructions you can be pretty sure you won't kill your trees following their advice.

I expect winter pruning is advised against with apricots because it theoretically could cause early flowering on a tree that already flowers way too early to be a reliable cropper at even mildly frost susceptible sites. I haven't seen research that either backs this up or refutes this but I've seen no difference in my own anecdotal experience. The apricots all seem to bloom at the same time no matter when they are pruned.

How much summer pruning I do on stonefruit depends on the vigor of the trees- even with very young trees I'm training. Pruning takes away vigor from an establishing tree so young trees are best guided with frequent pinch pruning to steer growth where you want it. However, on vigorously growing trees that get a bit away from you, there's probably a good argument for removing all rank vertical growth during the growing season.

On mature trees I prune during the growing season as much as necessary to keep the trees open, but not too much to cause a reduction in sugar. This is a balance that defies the provision of easy to follow instructions, but each fruit needs about 30 well lit leaves to achieve maximum quality. I especially want an open tree as fruit begins to ripen.

The injunction against pruning cherries and apricots during the dormant season comes from the susceptibility of both to fungal diseases at open wounds. Thus pruning in mid-to-late summer before serious rains commence (assuming it does rain where you live) or the weather turns generally damp.

Steve, apricots don't get much canker. Bacterial leaf spot is not affected by pruning as far as I know- you sure this applies to apricots?

With cherries this makes sense to me and it is normal not to prune peaches when completely dormant because of canker, But I've not heard this of apricots. Just asking for some further confirmation, please.

Although Cornell suggests pruning peaches only when in early growth, I prune them while dormant regularly and hundreds of trees at different sites. It seems that vigorously growing trees are not very susceptible to canker.

This is mainly a California issue, perhaps, but might apply elsewhere: (from the UC Ag. and Natrl. Res. site)

"Apricots and cherries can have a fairly short lifespan in many climate zones in California due to a disease called Eutypa. This disease is able to invade through pruning wounds especially during the wet winter months. This disease causes limbs or twigs to wilt and die suddenly in late spring or summer with the leaves still attached.
The bark may appear dark with an amber colored gumming on the branches.

To combat the disease and reduce the potential for Eutypa to infect trees, you should begin pruning your apricot and cherry trees during the later part of summer and early fall at least 4-6 weeks prior to rainfall. However, realize that you may be opening your trees to sunburn with summer pruning so be sure to paint exposed branches with a diluted white latex housepaint with 50:50 water to paint mix. Also avoid pruning if you are going to have an extended period of 100 degree plus weather. "

Think "fireblight" for stone fruits.

When living in So. Cal. many years back I also used to prune my peach tree during the dormant season without any problems. So far I've done the same here where it is much damper and I see no problems. Yet. But I do try to do most cherry and apricot pruning during the summer. This is not really an ideal climate for either (or peaches, for that matter) so I'm trying not to push my luck.

This post was edited by steve_in_los_osos on Sat, Aug 3, 13 at 14:43

Thank you Steve, I'm enough of a fruit nerd to find that very interesting even though I've never heard of that disease being an issue here in SE NY.

I was raised in Topanga Canyon in S. CA and the first tree I was a steward to was an apricot. The tree was probably ten years old when my family moved there in 1963. It is still growing vigorously today and I always pruned it when most dormant. It never actually went into complete rest.

University recs are based on commercial production issues and disease and insect pressure is often less in home plantings, I think. Still, it can't hurt to follow them when it is convenient.

I have struggled to grow apricots in my current location for about 25 years and I finally have my first major crop this year from a tree I planted on the southwest wall of my white house. I prune it during the growing season to direct it against the wall.

" However, realize that you may be opening your trees to sunburn with summer pruning"

I sometimes prune peaches too aggressively in the summer (after harvest) and this has happened. The sunlight burns the branches and gets canker started. Based on that I would recommend the same advice Hman mentioned, remove only rank vertical growth.

Where I've gotten into trouble is when I've removed all vertical growth leaving the scaffolds too exposed.

My trees tend to be so vigorous it's hard to resist cutting too much wood out of the tree in the summer (thus exposing too much scaffold) simply to stay ahead of the game.

Funny, here in the northeast I've noticed worst problems with "sunburn" on bark with dormant pruning. This is with major pruning of apple trees. I believe that the cause is not just exposure of previously shaded bark but also the reduced flow of sap due to a heavy reduction in foliage. If there is adequate sap flow the wood remains adequately cool, even when exposed to direct sun.

I've never scorched a peach tree by over pruning. The threat is probably less under the northeastern sun. By midsummer most hot days are quite humid, as well.

With different goals you will get different recommendations, hence the conflicting information.

Summer pruning is crucial for maintaining reasonably sized, easier to manage and productive trees. Winter pruning has its place, but generally forces vegetative growth at the expense of fruit production. There are exceptions such as pomegranates that fruit on new wood.

Other folks and texts may have different goals, but Summer pruning is the primary concept behind Backyard Orchard Culture.

I think it might be clearer to point out that the absolute dependency on primarily summer pruning to maintain size and productivity pertains to situations where the rootstock is pushing for a larger tree than the space being provided.

It has long been the standard method of managing espaliers to do most pruning during the summer, but after terminal bud set (between mid-July and mid-Aug in the northeast).

Where trees are growing in space more in harmony with the vigor of their rootstock, summer pruning is more about getting good color and reducing fungus pressure than increasing productivity or keeping the size of trees smaller.

With peaches it is also about keeping productive wood closer to the scaffolds, which means it would fall under the description of summer pruning to maintain a stouter more productive tree. However, in typical management, this summer pruning doesn't eliminate more vigorous pruning- usually done in spring around here.

Olpea, do you think where you've gotten leaf scorch the trees may also have been suffering from drought? Not severe drought, but where trees had plenty of water during pruning but then things dried out shortly after?

Hman,

I haven't experienced much leaf scorch on peach trees. Occasionally I see some silvering of the leaves when it's really dry but not too much.

I use a lot of mulch which may help the situation. As you know, mulch really holds moisture. Last year it was so very dry, but we had all the new peach trees mulched and really stayed on top of weed control. Many people couldn't believe we never watered the peach trees last year. In spite of the drought they looked fairly lush, like they were irrigated.

I suppose it doesn't surprise me you don't see any sunburn on peach scaffolds in the Northeast. We get more 100 degree days here. When the sun is overhead and the temps are up there, the exposed bark just can't cool itself enough.

I guess differences in climates dictate somewhat different cultural practices.

We don't get any Southwest injury here, which is nice. In the winter, the sun doesn't get as low in the sky as in the northern states. Snow doesn't stay on the ground very long either (in a normal year).

Here's my 4-in1 Frankenplum, the July varieties pruned back, the August not yet.

Olpea, I meant to type bark scorch. Brain left the page.