I had CHAT GPT make me a chart on comparing factors that favor higher brix in peaches and apples from most to least important. I don’t think you have to be a fruit nerd to find this interesting. In non-humid regions, pruning and training systems aren’t so important because you can control growth with deficit irrigation so light will be ample on the leaves that serve the fruit- leaves within about 8" of individual fruit without needing to keep shading leaves pruned.
This is a general guideline and certain factors may affect a given variety more than others, such as cool nights in the final stage of ripening for Honeycrisp apples. Every variety has genetic tendencies that affect outcomes in different ways. Certainly the low-acid extra sweet nectarines like Honey Royale are especially influenced by genetics making them significantly sweeter than others within their species. .
Factors influencing sugar (°Brix) in Northeast orchards with vigorous rootstocks
Notice how pruning & training now sits right alongside sunlight at the top. In humid, high-vigor conditions, it’s the key to unlocking leaf efficiency and fruit exposure.
Crop load and leaf health remain critical levers.
Day/night temperature swings matter a bit more in apples (because of starch conversion), but far less in peaches.
Warmer nights lead to more carbs being used for growth at the expense of fruit… mainly for apples- especially for Honeycrisp which depends more on carbs delivered during final ripening than other apples that store more starch earlier in the season.
I just spent another 15 minutes with CHAT to figure out how cool nights increase sugar in fruit. It turns out to be the result of reduced respiration in the fruit itself because it reduces the level of maintenance required to sustain the organism (the fruit itself) leaving more sugar in the fruit that is otherwise spent.
That make a lot of sense. But is counter to the dwarfing effect of high heat levels as well. I notice my apples lose a lot of leaves and replace them with new ones though. A different form of vegetative growth?
That would be helpful,
This year I’m getting exceptionally sweet fruit.
I just had a nectaplum and also Flavor Queen pluot. Both loaded with sugar. I didn’t test brix.
If I remember when I go home if I can find the device. I may test them.
Not just sweet but flavorful. Geopride pluots had layers of different interesting flavors this year. I’m still waiting on four other pluots to ripen. Dapple Dandy should be awesome this year. I love the size and how well it produces. Also resist brown rot better than my other pluots. Even in my worst years where I lost all my Geopride Dapple only had a few rot.
Anthony et al. (2021, Agronomy) – Emphasize that optimizing light interception and distribution via modern training systems (like fruit walls) boosts both yield and fruit quality in peaches. Light access is fundamentally tied to SSC potential. MDPI+2ResearchGate+2
2. Pruning & training system
Ikinci et al. (2014, PMC NCBI) – Found that summer pruning can significantly reduce available carbohydrates — demonstrating the delicate balance between leaf removal (for light) and carbohydrate supply. PMC
Mazzoni et al. (2022, MDPI) – Combined pruning and thinning levels to show how branch structure and crop load jointly influence peach SSC and fruit quality. Purdue e-Pubs+4PMC+4MDPI+4
3. Crop load / thinning balance
Mazzoni et al. (2022) – As above, reductions in crop load consistently increased SSC in peaches across two seasons and cultivars. PMC
4. General Brix-influencing factors
VegNet (Ohio State, 2020) – Provides a broad overview of factors influencing °Brix, including variety, irrigation, plant density, sampling timing, temperature, and light — applicable across tree fruits. PMC+15u.osu.edu+15growingfruit.org+15
5. Pruning effects on fruit quality (pears & apples)
Goke (2020, MDPI) – Showed that summer pruning (especially combined with fall/winter pruning) improves dry matter and marketable quality in pears by boosting light exposure, protecting against disorders, and improving color (parallels apples/peaches). MDPI+4MDPI+4ResearchGate+4
Summary Table
Factor
Supporting Study / Insight
Light & canopy design
Anthony et al. (2021): canopy architecture drives light distribution and quality.
Pruning strategy
Ikinci et al. (2014): summer pruning affects carbohydrate reserves.
Pruning + thinning
Mazzoni et al. (2022): combined effects on SSC in peaches.
Alan does your robot understand where you’re posting this, why is it insulting us ()
anyway what conditions have you personally noticed to make higher sugars in your trees? where you are does drought/water make a big difference too, or is it just getting good sun exposure. do you personally prune differently between a peach and say, an apple? or do you go for open center both?
First of all, I should say that I’m still sometimes mystified when trees fail to produce high quality, high brix fruit. Right now I’m harvesting some Satsuma plums that aren’t worth eating because half are too low sugar- and who wants to bite to find out? While at another site a Sat. tree that was not tended since I did some pruning in spring and vigorously closed over the crop with new growth has as good a plums as I would want. My Red Gold nectarine was thinned well and we’ve had mostly warm sunny days since the 2nd week of July and the fruit hasn’t even reached 13 brix- but then the later ripening Fantasia in a less light exposed part of my property (but also drier and shallower soil) is showing signs of being very good based on first fruit to ripen.
I’ve never evaluated my own methods with any efforts of controlled experiments and the experiments done on this subject that the chart is based on are relatively limited in region and quantity- these are only guidelines that will not settle all the mysteries.
I generally get high quality fruit from my trees and the much greater quantity of trees I manage, but my methods are about keeping every orchard well managed by spreading the work over the year as much as possible- a lot of summer pruning makes it possible for me to do all the winter pruning necessary before I’m completely closed in with the requirements of my springs.
Schedule for my own orchard: Winter pruning of apples and pears- not a lot of labor because of pruning done during the growing season. For the first 15 years or so I train my apples and pears to a central leader form with two tiers because the first starts 5’ up the tree to protect branches from deer. Once trees reach a certain size I may take out the top tier or I may keep cycling in and out the top branches (the cycling starts much sooner.
**I spring prune stone-fruit sometime between first growth and late bloom. During bloom I will remove whole clusters of blossoms from a couple varieties of apples most important to me to get good annual cropping, such as Goldrush. **
**Shortly after petal fall I begin thinning fruit of peaches, nects and important apple varieties, I also mop out a lot of new shoots attached to big wood that will not serve my fruit and only shade the shoots that do that and will build the flowers for next season. I do a similar kind of pruning as I thin fruit for stone fruit. I start with earliest fruiting peach and nect varieties. I usually thin my plums after I have a handle on my peaches and nects- my most important plums and pluots bear late, anyway. **
I continue thinning fruit well into summer and keep my trees pretty open by pruning them once or twice during the summer- this year twice because of so much vegetative growth.
I should add that for vigorous apple trees, summer pruning vastly reduces the amount of spray needed to protect them from apple aka Marsonnina leaf blotch and probably reduces all summer fungus problems in itself by speeding the evaporation of dew and recent rain. Summer pruning generally allows you to get good spray coverage with half the spray.
It sounds like a good part of the brix problems in humid areas is too much vigor resulting in excess shading. I can believe that. There needs to be good light on the leaves near the fruit. Here outdoors I have to irrigate twice a week heavily to keep young trees growing. Old apple trees quit growing in late spring. Stone fruit quit also but it has to get a lot drier. Light is high unless it’s the interior of a large tree.
In my greenhouse light is 50% of outside but it’s an even diffused light that penetrates well into a canopy of leaves. Vigor is much higher in the GH than outside. But I summer prune often, probably 6-8x per year. And I thin heavily and early. That results in high brix fruit if the tree isn’t over watered.
No. I try to leave the graftwood I’m going to wan the following spring and keep it in storage for as short a time as possible after the leaf buds are fully stored with energy. Not sure those leaf buds would come out with the same vigor if they were brought in during the growing season. It would be a nice experiment- but I don’t have the refrigerator space when I’m storing a lot of stone fruit.
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