Postharvest nutrition in stone fruit: the next crop is made in July

An apricot tree carrying a full crop shortly before harvest — An apricot tree with a full crop shortly before harvest. **That crop is the result of last summer**: the flower buds that produced it were differentiated and fed in the months after the previous harvest.

Savvas Pastopoulos, Agronomist MSc — Pastopoulos Agricultural Ltd, Neos Mylotopos, Pella

Something happens in sweet cherry and apricot that does not happen in most fruit crops: harvest ends in May or June, and the tree is left in full leaf for another four or five months with no fruit on it. Those months are usually treated as dead time. They are not. They are the period in which the next crop is made — and made twice over: once in the buds and once in the reserves. In this article every recommendation is accompanied by the study that supports it.

90%of the nitrogen in
spring spur leaves comes
from reserves

+40%nitrogen in the
flower buds with
autumn urea

+4.25 °Cbetter cold
hardiness

7–9 weeksafter harvest
the pistil is
formed

Contents

Why the period after harvest is the most underestimated
What happens in the buds: sweet cherry and apricot
The reserves and their remobilisation
Nitrogen after harvest
When autumn fertilisation is pointless
Boron — the target with the best return
Zinc
Water: without it nothing works
Temperature and doubled fruit in sweet cherry
Early defoliation cancels everything out
How foliar sprays are applied correctly
The programme as a calendar
Sources

1. Why the period after harvest is the most underestimated

In most fruit crops harvest comes close to leaf fall and the tree has little time afterwards. In sweet cherry and apricot the opposite happens. The canopy works at full intensity through a whole July, August, September and October — and all of that photosynthetic product, together with whatever the root takes up, goes into two things and two only:

The differentiation of the flower buds from which next spring's bloom will come.
Loading the reserves in root, trunk, scaffold limbs and buds.

The critical peculiarity of stone fruit In sweet cherry, apricot, peach and nectarine, pollination and fertilisation take place before the leaves have fully expanded. At the moment the tree is flowering and setting, therefore, it has no photosynthetic machinery to feed the process. Whatever it needs, it takes from the reserves it built the previous summer and autumn.

Sources: 1

2. What happens in the buds: sweet cherry and apricot

This is not theory. It has been observed under a scanning electron microscope, bud by bud, from May to November.

Sweet cherry — the timetable

Differentiation begins at about the same moment in all cultivars, with the first buds visible in mid to late May. No clear relationship was found between harvest date and the date differentiation began.
The sequence is constant: first a pentagonal ring of sepal primordia, then the petals, then the anthers, and last of all the pistil.
The rate of progress follows the ripening order: in the early ‘Chelan’ the pistil primordia are visible in early August, whereas in the late ‘Sweetheart’ about three weeks later.
Overall, the start of pistil development occurs roughly 7 to 9 weeks after harvest.

Observations on ‘Chelan’, ‘Tieton’, ‘Bing’, ‘Skeena’ and ‘Sweetheart’.

Sources: 2

Apricot — the timetable

The initial phase of differentiation starts in mid to late July, followed by differentiation of the floral organs.
In deciduous fruit trees generally, initiation, differentiation and organogenesis of the flower bud all take place within the summer–autumn period preceding bloom.
The abnormalities of the flower buds — the well-known problem of sterile apricot flowers — are linked to precisely this first period of development.

Sources: 9 10

The conclusion that changes the management When in mid-July the tree has been emptied of fruit and “nobody looks at it”, inside its buds the sepals, petals and anthers of next spring are being differentiated. A tree that is thirsty, hungry or losing leaves at that moment does not pay for it this year. It pays for it next April.

3. The reserves and their remobilisation

During autumn, the nitrogen inside the plant is mobilised and transported to the roots, where it stays in storage until the next season. In spring the reverse journey follows.

How important are those reserves? The cleanest measurement comes from apple, using labelled nitrogen:

Where the nitrogen ends up next spring	Proportion coming from reserves
Nitrogen of the shoots	50%
Nitrogen of the spur leaves	90%
Nitrogen of the fruit	60%

Sources: 1 13

The 90% for the spur leaves is the figure to hold on to. The spurs are exactly the positions on which sweet cherry fruits. The spur leaf that will feed the cherry in May is built almost entirely from nitrogen stored the previous September.

4. Nitrogen after harvest

What autumn urea achieves in sweet cherry

Postharvest foliar urea is not a new idea: it had already been tested on pear, with a measurable response from the tree [21]. In experiments with 3.5% foliar urea on sweet cherries on dwarfing rootstocks, over four successive application periods from late August to late October:

An increase in nitrogen reserves in the flowering spurs of up to 40%.
Improved cold acclimation, with hardiness up to 4.25 °C better than the control.
Early defoliation had a negative effect both on the nitrogen reserves and on spur leaf development in spring.

Sources: 3

How much is actually absorbed

The efficiency of autumn foliar nitrogen ranges from 30% to 80%, depending on the weather conditions.
With 2% urea, 48% absorption was measured.
In a comparison of application timings in sweet cherry, uptake efficiency was 65.7% for the spring application against 37.4% for the summer one — but the summer nitrogen was distributed not only to trunk and roots but also to the buds, which is exactly the target here.

Sources: 11 14

Exactly when the spray is made The rule is clear and is repeated in every source: after harvest, but before natural leaf fall — at the moment the leaves are beginning to yellow. The leaf has to be still alive in order to absorb, but the tree has to have already entered the phase of transport towards the root, the trunk and the buds.

In a trial with labelled urea on fruiting limbs of ‘Bing’/‘Gisela 6’ sweet cherry, with four application dates after harvest, the earliest application gave the highest nitrogen use efficiency, while in all treatments the urea was transported from the leaves to the other organs, with the highest values in the fruiting section.

Sources: 12

5. When autumn fertilisation is pointless

The timing of the application and the texture of the soil together determine how much of the nitrogen the tree will actually use [23]. This is the point that separates agronomy from selling fertiliser. Autumn sprays pay off only where there is a real deficiency. They are not tonics.

The most instructive study — and it is on sweet cherry

On mature ‘Burlat’ sweet cherries in central Poland, on a coarse-textured soil with adequate phosphorus, potassium, magnesium, calcium, iron, manganese, zinc and copper — but low boron, autumn sprays of nitrogen, boron and zinc were tested over three years. The result:

The sprays had no effect at all on flower bud damage from cold, on the nitrogen status of the tree, or on the soluble solids of the fruit.
Only boron improved the reproductive response. Nitrogen, on trees that did not need it, did nothing.

Sources: 5

When nitrogen is needed — and when it is a mistake

It is needed when:

There is a documented deficiency. In sweet cherry, a nitrogen concentration in recently matured leaves in midsummer below 2.0% indicates deficiency. The sufficiency range is 1.7–2.5%.
The orchard has carried a heavy crop and the trees are showing a loss of vigour.

It is a mistake when:

Levels are adequate and vigour is balanced — the spray is then simply ineffective.
There is excessive vigour. There the extra nitrogen is counterproductive, and leaf analysis can mislead: in very vigorous tissue the nitrogen concentration is diluted. That is why the assessment has to combine leaf analysis and a visual judgement of vigour.

Sources: 1

6. Boron — the target with the best return

If there is one element for which postharvest application has clearer documentation than spring application, it is boron.

What it does and why in autumn

Boron is fundamental to pollen germination, pollen tube growth and fruit set. Demand for it peaks at exactly the start of the season.
In the xylem it has low mobility. In Prunus, Malus and Pyrus, however, it has sufficient phloem mobility — and that is what makes an autumn foliar spray actually reach the buds.
Autumn application is more effective than spring application in raising boron in the flowers and improving fruit set.

Sources: 15 24

In apricot: the experiment every apricot grower should know

In the Malatya region of Turkey, over four years (2009–2012), on unirrigated apricot trees of cultivar ‘Hacıhaliloğlu’, autumn foliar application of boron, urea, and the combination of the two was tested. The results:

The proportion of sterile flowers was reduced. That is the classic problem of apricot.
Yield increased.
The highest concentrations in the buds were measured in the boron + urea treatment: 16.53 ppm boron and 1.56% nitrogen.
The combination of boron 1,000 ppm + urea 3% improved flower development and fruit set.

Sources: 4

In sweet cherry In the ‘Burlat’ trial cited above, the boron and zinc sprays raised boron levels in the flowers and in the midsummer leaves, and improved fruit set and yield. Independently, boron fertilisation has been documented to affect yield and fruit quality in sweet cherry.

Sources: 5 7

Caution: boron has the narrowest margin of all the elements The distance between deficiency and toxicity is very small. The sufficiency range in the leaves is 20 to 80 mg/kg, sampled in midsummer on leaves that have completed their growth. One spray a year is enough to prevent deficiency. The leaf is a better indicator than the soil. And one further recommendation: boron is not recommended on young, non-bearing trees.

Sources: 1 24

7. Zinc

Sweet cherry, along with apple, is among the species most sensitive to zinc deficiency. The symptoms are characteristic: small leaves, chlorosis, rosetting and short internodes. Levels below 25 mg/kg in recently matured leaves indicate deficiency.

Deficiency appears mainly on cold, wet, sandy and alkaline soils with a pH above 7.5, where zinc is fixed. Under those conditions the problem is not a shortage of quantity but an inability to take it up — and that is why soil application is ineffective.

The limitation of zinc, and what it means in practice Zinc has low remobilisation and a high capacity for being bound inside the plant. The result, as measured in both sour cherry and sweet cherry, is that autumn application improved levels in the buds and the flowers, but did not affect overall leaf levels. So where the deficiency persists, repeated applications are needed rather than one.

Sources: 6 22

8. Water: without it nothing works

Every correct spray can be made and nothing gained, if the tree has no water during the differentiation period. And in apricot this has been measured in the most direct way.

What water stress does to apricot buds

In two-year-old apricot trees of cultivar ‘Portici’ subjected to controlled water stress in June, in July and in October, with irrigation restored afterwards:

Both summer stress periods caused a temporary halt in flower differentiation.
Trees stressed in June were able to recover; those stressed in July showed a marked delay.
All stress treatments caused slower development of the xylem vessels inside the bud, changes in bud size, in flowering intensity, and flower abnormalities.

Sources: 8

Translated to the orchard: July — that is, precisely the month after the apricot harvest — is the worst month for the tree to go thirsty. Irrigation does not stop at harvest.

9. Temperature and doubled fruit in sweet cherry

Doubled fruit — polycarpy, that is more than one pistil in a flower — is one of the leading causes of fruit rejection. And it is created the previous summer, within the period discussed here.

Finding	Source
Exposure to 35 °C day / 25 °C night from June to September increased doubled fruit in ‘Satohnishiki’	[16]
High temperature, and not water stress, is responsible for doubled fruit	[17]
80% shading during differentiation reduced doubles from 47% to 24%	[18]
In ‘Bing’, sensitivity extends from late July to early September, peaking in early August. Once pistil development has advanced, the bud is no longer sensitive	[2]

What worked in practice — and what should be avoided

In a commercial ‘Tieton’ orchard with a natural doubling rate of around 30%, with treatments from mid-July to mid-August:

Overhead evaporative cooling: a 50% reduction (applied only when the temperature exceeded 34 °C, in cycles of 20 minutes on and 10 minutes off).
Kaolin: a 45% reduction, with three applications to maintain coverage.
20% shading: a 37% reduction.

Overhead cooling dropped tissue temperature by about 5 °C, kaolin and shading by about 2 °C.

And the warning: under-canopy microsprinklers were ineffective and in fact slightly raised canopy temperature, because the increased humidity reduces the vapour pressure deficit and therefore the foliage's own evaporative cooling. Running under-canopy sprinklers with the aim of reducing doubles is not recommended.

Sources: 2

10. Early defoliation cancels everything out

Everything described above presupposes one thing: that the foliage will stay on the tree, healthy and functional, until natural leaf fall.

Early defoliation had a negative effect on nitrogen reserves and on spur leaf development the following spring in sweet cherry.
In a separate trial on ‘Selah’ sweet cherry, early defoliation reduced yield and the concentration of nutrients in the buds.

Sources: 3 22

Crop protection in July to September is nutrition Anything that defoliates the tree after harvest — cherry leaf spot and other foliar diseases in sweet cherry, spider mite, weakening from drought — does not cost “just leaves”. It cuts short the one period in which the reserves are loaded. A tree left bare in September flowers weakly in April, however correctly it is fertilised in the spring.

11. How foliar sprays are applied correctly

The application conditions

Temperature: not below 20 °C and not above 29 °C.
Wind: strong wind shortens the drying time of the droplet and therefore the absorption.
Relative humidity: low humidity affects droplet size and how long it stays on the leaf surface.
Sulphate salts — such as zinc sulphate — are applied only once the temperature has fallen below 27 °C.

Two technical details that matter

The urea must have a biuret content below 0.25%. Biuret is phytotoxic.
Mixing the trace elements with urea improves their uptake. It is not a combination of convenience — it is a documented enhancement.

Sources: 1 19 20

The concentrations tested in the literature

Urea: 2% on apple [14], 3% on apricot [4], 3.5% on sweet cherry [3].
Boron: 1,000 ppm combined with 3% urea, on apricot [4].
Zinc: zinc sulphate; the general recommendation for apple and sweet cherry is a higher rate than for peach and nectarine [1].

These figures are experimental, from particular conditions and cultivars. They do not transfer unchanged to every orchard. The choice of rate is always made on the basis of leaf analysis, the condition of the block and the authorisations in force.

12. The programme as a calendar

Period	Sweet cherry	Apricot
Immediately after harvest	Fruiting-wood pruning, irrigation restored to full rate, foliage protection.	Pruning, full irrigation — July is the most critical month.
Midsummer	Leaf analysis on recently matured leaves. It is the only basis for deciding whether an autumn treatment is needed and for which element. Targets: N 1.7–2.5%, B 20–80 mg/kg, Zn above 25 mg/kg.
Late July to early September	Window of sensitivity for doubled fruit. In a heatwave, canopy cooling measures. No under-canopy sprinklers.	Differentiation of the floral organs. No water stress.
Autumn, before the leaves yellow	Foliar sprays — only for the elements the analysis showed to be deficient. Nitrogen for the reserves and cold hardiness, boron for fruit set, zinc where there is a deficiency.
Until natural leaf fall	The foliage stays on and healthy. Every week of early defoliation is a loss of reserves.

Harvested apricots of the Rouge Cot cultivar — Harvested apricots. **Size and colour are this year's work; the number of fruit, though, was decided last summer**, during flower bud differentiation.

An apricot tree with heavily laden limbs in a productive orchard — Even, dense fruit set along the whole length of the limb. **This picture is the definition of a successful postharvest period the previous year:** buds that differentiated without stress, with adequate boron and adequate nitrogen reserves.

The five things to keep

The next crop is made from July to October, not in March.
90% of the nitrogen in the spur leaves comes from the previous year's reserves.
Autumn sprays work only on a real deficiency. Without leaf analysis they are a lottery.
Boron is the element with the clearest documentation for autumn application — and in apricot it reduces sterile flowers.
Water and foliage. Without those two, no fertiliser matters.

13. Sources

The numbers in the text refer to the list below.

[1] Sallato, B. (2024). Fall Nutrient Sprays in Tree Fruit. Washington State University Tree Fruit Extension, Fact Sheet FS365E. The main reference text for the sufficiency thresholds, the application conditions and when a spray is pointless.
[2] Whiting, M. and Martin, R. (2025). When and How to Reduce Doubling in Sweet Cherry. WSU Tree Fruit. Source for the differentiation timetable in sweet cherry, the window of sensitivity and the results of the cooling measures.
[3] Ouzounis, T. and Lang, G. (2011). Foliar applications of urea affect nitrogen reserves and cold acclimation of sweet cherries (Prunus avium L.) on dwarfing rootstocks. HortScience 46(7):1015–1021. Source for the 3.5% urea, the 40% increase in spur reserves, the 4.25 °C of hardiness and the effect of early defoliation.
[4] Karlıdağ, H., Eşitken, A., Turan, M. and Atay, S. (2017). The effects of autumn foliar applications of boron and urea on flower quality, yield, boron and nitrogen reserves of apricot. Journal of Plant Nutrition 40(19):2721–2727. The main study for apricot: reduction of sterile flowers, increase in yield, 16.53 ppm B and 1.56% N in the buds.
[5] Wójcik, P. and Morgaś, H. (2013). Response of ‘Burlat’ sweet cherry trees to postharvest sprays of nitrogen, boron and zinc. Journal of Plant Nutrition 36(3):503–514. Source for the finding that only boron paid off where the other elements were adequate.
[6] Wójcik, P. and Morgaś, H. (2015). Impact of postharvest sprays of nitrogen, boron and zinc on nutrition, reproductive response and fruit quality of ‘Schattenmorelle’ tart cherries. Journal of Plant Nutrition 38(9):1456–1468.
[7] Wójcik, P. and Wójcik, M. (2006). Effect of boron fertilization on sweet cherry tree yield and fruit quality. Journal of Plant Nutrition 29:1755–1766.
[8] Cirillo, C. and co-workers (2021). Different summer and autumn water deficit affect the floral differentiation and flower bud growth in apricot (Prunus armeniaca L.). Agronomy 11(6):1226. Source for the halt in differentiation caused by water stress and for the severity of July stress.
[9] Cirillo, C. and co-workers. The effect of summer shading on flower bud morphogenesis in apricot (Prunus armeniaca L.). Central European Journal of Biology. Shading in July and August with histological monitoring of differentiation.
[10] Flower bud differentiation and development characteristics of Prunus sibirica L. and Prunus armeniaca L. Acta Horticulturae 1450. Source for the start of differentiation in apricot in mid to late July.
[11] Neilsen, D., Millard, P., Herbert, L.C., Neilsen, G.H. and co-workers (2010). Isotopically-labelled nitrogen uptake and partitioning in sweet cherry as influenced by timing of fertilizer application. Scientia Horticulturae. Source for the uptake efficiency of 65.7% against 37.4%.
[12] Distribution and recycling of canopy nitrogen storage reserves in sweet cherry (Prunus avium L.) fruiting branches following ¹⁵N-urea foliar applications after harvest. Acta Horticulturae 1020; also published in Ciencia e Investigación Agraria 41(1):71–80 (2014). Source for the superiority of the earlier postharvest application.
[13] Neilsen, G.H. and Neilsen, D. (2003). Nutritional requirements of apple. In: Ferree, D.C. and Warrington, I.J. (eds), Apples: Botany, Production and Uses, CABI Publishing, pp. 267–302. Source for the 50%, 90% and 60% figures.
[14] Guak, S., Neilsen, D., Millard, P. and Looney, N.E. (2004). Leaf absorption, withdrawal and remobilization of autumn-applied urea-N in apple. Canadian Journal of Plant Science 84:259–264. Source for the 48% absorption with 2% urea.
[15] Brown, P.H. and Hu, H. (1996). Phloem mobility of boron is species dependent: evidence for phloem mobility in sorbitol-rich species. Annals of Botany 77:497–505. Source for the phloem mobility of boron in Prunus.
[16] Beppu, K., Ikeda, T. and Kataoka, I. (2001). Effect of high temperature exposure time during flower bud formation on the occurrence of double pistils in ‘Satohnishiki’ sweet cherry. Scientia Horticulturae 87:77–84.
[17] Beppu, K. and Kataoka, I. (1999). High temperature rather than drought stress is responsible for the occurrence of double pistils in ‘Satohnishiki’ sweet cherry. Scientia Horticulturae 81:125–134.
[18] Beppu, K. and Kataoka, I. (2000). Artificial shading reduces the occurrence of double pistils in ‘Satohnishiki’ sweet cherry. Scientia Horticulturae 83:241–247.
[19] Fernández, V., Sotiropoulos, T. and Brown, P. (2013). Foliar Fertilization: Scientific Principles and Field Practices. 1st edition, International Fertilizer Industry Association, Paris.
[20] Sánchez, E.E. and Righetti, T.L. (2005). Effect of postharvest soil and foliar application of boron fertilizer on the partitioning of boron in apple trees. HortScience 40(7):2115–2117.
[21] Sánchez, E.E., Righetti, T.L., Sugar, D. and Lombard, P.B. (1990). Responses of ‘Comice’ pear trees to a postharvest urea spray. Journal of Horticultural Science 65:541–546.
[22] Sallato, B. and Whiting, M.D. (2021). Early defoliation reduced yield and bud nutrient concentration in ‘Selah’ sweet cherry. Acta Horticulturae, IX International Symposium on Mineral Nutrition of Fruit Crops, Tel Aviv.
[23] Weinbaum, S.A., Klein, I., Broadbent, F.E., Micke, W.C. and Muraoka, T.T. (1984). Effects of time of nitrogen application and soil texture on the availability of isotopically labeled fertilizer nitrogen to reproductive and vegetative growth of mature almond trees. Journal of the American Society for Horticultural Science 109:339–343.
[24] Faust, M. (1989). Physiology of Temperate Zone Fruit Trees. John Wiley & Sons, New York. Source for the superiority of autumn boron application and for the one spray a year.

Disclaimer This text is informative and educational in character and summarises published scientific findings. It does not constitute individual agronomic advice. The concentrations and rates mentioned come from experimental trials under particular conditions, cultivars and soils, and they do not transfer unchanged to every orchard. Every nutrition programme is drawn up after leaf and soil analysis and an on-site assessment by a licensed agronomist, in line with the authorisations in force in the country concerned. Pastopoulos Agricultural Ltd accepts no liability for any damage arising from the use of the information in this text.