Greenhouse Peach – UFO & ABC Training

Peach Tree trained as an Upright Fruiting Offset (UFO),
using an Alternate Biennial Cordon (ABC) method

What’s wrong with Traditional Peach fan-training?

Unlike apples and pears, peaches do not fruit on older wood. Instead, flowers and fruit are produced on one year old shoots. Therefore, you need to make sure there is a continuous supply of new shoots to provide next year’s fruit. This supply of new shoots needs to be planned for, so that you always have new shoots being added to your peach. One way of thinking about it, is that each year you are growing two crops: (1) new shoots, which will become next year’s fruiting shoots and (2) fruiting shoots, which were last year’s new shoots. To organise these two kinds of shoots, and keep them alternating each year takes a bit of planning. Well, actually, a lot of planning. In fact, it took me several years just to get my head around the concept, at which point, I realised that my initial fan-trained layout was going to be a nightmare to maintain long term.

Traditionally, peaches are trained as fans, consisting of a framework of permanent branches splaying out from a short central trunk (as in the photo below.) Side shoots from these branches are then tied in, and fruit forms on these side shoots in the next season. This works well when the fan is young, because there is a constant supply of new shoots being produced as the fan is trained outwards towards the edge of its allotted space. However, as the wall becomes covered, sufficient two year old (fruited) shoots must be removed to make space for the new shoots which will carry next year’s fruit. In fact, it becomes apparent that one needs to have a strategy, so that there is space for 50% of the growth to be replacement shoots (which ones, and where?), while the other 50% need to be this year’s fruiting shoots. The necessity of managing both fruiting shoots (which grew last year) as well as growing new shoots (which will fruit next year) quickly becomes a headache to manage. How does one remember which is which? and ensure there are sufficient replacement shoots to maintain fruiting each year? And where exactly are these going to fit when the permanent branches of my peach are so close together?

Understanding peach pruning requirements

Peaches need a two year cycle of shoot growth and replacement. To maintain fruiting potential from year to year, therefore, one wants to maintain 50% fruiting shoots (A) and 50% replacement shoots (B) on the tree each year, which I was struggling to achieve with the fan-trained form. At the end of each year (in winter or early spring), the shoots that have previously fruited (A) need to be removed, pruning them back to a new bud or young shoot close to their base, which will be trained in over the year as a replacement shoot (hence becoming this year’s new shoot, B). Meanwhile, last year’s (B) shoots are now 1 year old, so will carry fruit (so these are now fruiting shoots, A).

In this way, the growth pattern reverses each year. This A/B, B/A management is not only tricky to visualise and stay on top of, but even harder to arrange on a wall in a way that is easy to understand and sustainably maintain. I realised that it was going to be extremely difficult with my original fan-trained layout, as there was no logical location or space for these A/B shoots between the main branches of the fan.

Compounding this problem is the fact that peaches create a lot of excess vegetative growth during the growing season, with shoots easily growing 4-6ft (1-2m) in one season. To keep on top of pruning, therefore, it helps to be very clear about what should be removed and what should be kept. With the fan layout I was never quite sure what growth to keep and what to remove: I couldn’t come up with a system that made sense.

This is what led me to undertake a radical rethink of my peach tree training: what I call the ABC modified UFO method, no less! Lets take each of these acronyms in turn…

Upright Fruiting Offset (UFO) training

Upright Fruiting Offset (UFO) training is being used commercially for field-grown cherries and other high intensity fruit production, grown flat on horizontal wires. The method appears perfectly suited to wall grown fruit. Apparently, some growers are using the UFO method for peaches, although it hasn’t been widely adopted yet, so there isn’t a great deal of information available.

So how can the UFO method be applied to wall-trained fruit trees?

With vertical offset training, the main framework of the fruit tree consists of a single or pair of horizontal main branches low on the wall (coloured orange in the diagram below). From these main branches, vertical shoots are trained upwards and are tied in, until they reach the top of the wall. For spur-forming fruits such as apples and cherries that this method has been designed for, these uprights become permanent fruit-bearing shoots. This system is known as the Upright Fruiting Offset system (UFO).

Unfortunately, peaches do not fruit on spurs, but rather on one year old wood, which needs to be continually provided for continued fruiting. So, the UFO system needs to be modified to accommodate this two year shoot/fruit cycle. The uprights (cordons) will need to be pruned back every two years, and fresh new growth trained in to replace them. To ensure fruiting is continuous, these will need to be staggered, so in any one year, half the cordons are fruiting, and the other half are renewal growth. I call this modification for peaches the ABC system (Alternate Biennial Cordon system.)

Alternate Biennial Cordon (ABC) System

For peaches, my ABC system involves growing equal number of fruiting and replacement shoots on the tree. These are indicated by the blue (fruiting) and green (replacement) shoots, above. To accommodate this biennial growth pattern, these shoots are treated in an alternating A/B pattern. In one year, the blue shoots (which grew the previous year), will be fruiting, while the green stems are grown up and will fruit the following year. Next year, the roles will reverse, and it will be green’s turn to flower and fruit, while the blue stems (which fruited in the first year) will be cut down, and a new shoot will be trained in its place. By laying out the vertical shoots in an alternating pattern, this biennial treatment is easy to understand, and it ensures the wall can be used to its maximum potential. Unlike the fan trained method, there are only two permanent (horizontal) branches, leaving the wall above fully available for fruiting and replacement shoot cultivation.

As well as offering an efficient use of wall space, this arrangement makes the whole biennial pruning cycle much clearer: It is easy to understand exactly which shoot is doing what each year, so it is obvious what and when to prune. Any extraneous growth is easy to identify and can be pinched back or rubbed out immediately. The 1 year old fruiting shoots actually need very few leaves to nourish the growing fruit, so most of their side shoots can be rubbed out in the spring, as long as a few leaves are maintained.

The only issue I see is the long term viability of replacement bud production at the base of the pruned cordons. This, however, is just as much an issue with fan-trained peaches, as old wood can become unproductive over time, so I’ll just have to see how it goes as I go along. I assume that pruning the old fruiting shoots back to a 5-10cm stump will stimulate the formation of new buds, but how long this can be maintained remains to be seen.

How I got my fan-trained peach into shape

The above method would be ideal if you were starting from scratch. Unfortunately, I only realised this a few years in to training my peach as a fan, so I had to change direction and undertake some serious pruning to reshape it. I did this in August 2022.

To create the new structure, I cut back all of the diagonal branches that were in my existing fan, only allowing two roughly horizontal ones to remain, almost like a step-over apple. These became my permanent horizontal framework (orange). Biennial shoots were then trained up vertical strings from here (blue and green in the diagram above) which were roughly 12 inches (30cm) apart. I detail this butchery towards the end of my earlier article: Fan Training A Greenhouse Peach

So far, I think I have made the right decision. Although it’s going to take a couple of years to get all of the uprights into their A/B pattern. I’ll keep you updated as the years go by, so, read on (and check back now and then) to see how it all worked out…

Read on for annual updates

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LATE MARCH — Considering how hard I pruned it last year, I was surprised by the amount of flowers that appeared on the stems this spring. Despite looking quite spindly at this time of the year, over the next six weeks, the tree put on a lot of growth… Look! See!…

MID-MAY — Look how quickly it has grown! The new shoots are sticking out in all directions. Time to get in there and get it back in shape.

In future years, once I have got my routine worked out, I will remove misaligned buds and shoots throughout April, tying in as I go, which will avoid this kind of chaos, but this year, while I am getting the hang of things, I wanted it to develop some long shoots that I could tie in.

First, I located the tall one-year-old shoots that I had in place at the end of last year. The young fruits developing along these stems only need a few leaves above or beyond them, so I pinched out all the side shoots that had started to develop, leaving just one or two leaves. I also took out the tips at the greenhouse eves to stop them growing taller.

Next, working from left to right, I selected and tied in long, new shoots, to create a series of verticals parallel to the existing one-year-old fruiting shoots, with an approximate spacing of 8 inches. As I did this, I cut out shoots that were too small, of didn’t fit into the scheme, and especially any that were growing towards the wall:

This filled in approximately one third to half of the wall space. As you can see, the main horizontal branch to the left and right are still rather immature and have not produced long enough growth to create new uprights on the parts of the greenhouse wall yet. The plan is to repeat the process above next year, and gradually fill in the remaining wall space.

I had been somewhat confused about how to progress this stage in my management plan, as my aim is to end up with an alternating series of vertical canes: new…old…new…old…new…old…, but how does one get there? Currently I have this:

MAY 2023 — So, here is the situation: The main framework (orange) is in place, and the beginning of alternating vertical shoots. Currently, there are three fruiting shoots (last year’s growth – blue) and eight new shoots (this year’s growth – green)

Normally, all the green shoots would be left to flower and fruit next year (becoming next year’s blue shoots). The blue shoots will be cut down to a few inches from their base, so that they will grow replacement shoots next year which can be trained in their places (these will become next year’s green shoots). However, to produce the alternating pattern I want with half blue and half green shoots, at the end of this year, I will cut out some of the green shoots — treating them as if they were blue. If all goes to plan, then by this time next year, I should have the proper alternating pattern.

July 2023 — The tree fruited very well this year. After thinning, I had approximately 35 peaches which grew to harvest. The photo above was taken shortly after pruning back the excess growth which was shading the peaches. I think I need to do this earlier to enable the peaches to get more sunlight earlier. As you can see many of the peaches are rather green/anaemic.

A few weeks later and some of the peaches were ready for eating. This year’s peach harvest was the best so far (in terms of quantity). Their flavour varied from just OK to quite good. The flesh was generally tender, occasionally melt-in-the-mouth. Sometimes the sweetness was lacking, other times the acid-tang or fragrance was lacking. A few of the peaches were exceptionally good. Generally, these were ones that were less crowded, larger and in full sun.

Cretaceous Earth as an organic spider-mite treatment
In the photo above, you can see that the older leaves have a white bloom on them. This is due to a spray of Diatomaceous Cretaceous Earth (not the same as Fuller’s Earth). This white powder is used to treat mites and fleas on pets, and treat ant colonies, woodlice and other insect pests. It consists of the fossil remains of microscopic sea creatures. These tiny shell-fragments are inherently sharp — almost like microscopic shards of glass — which can puncture the carapaces of tiny insects, leading them to die by dehydration. Cretaceous earth, is however, harmless to larger insects, pets and children. It is only effective when dry, however, and is usually applied by sprinkling or dusting around ant nests or in pet or hen housing. I recently learned that it can be mixed with water and applied to plants using standard pump sprays. I sprayed the leaves of the peach in an attempt to prevent spider-mites which are always a problem in the dry atmosphere of a greenhouse. It certainly seems to have worked.

February 2024 — I gave the tree (and greenhouse wall) a second winter wash using dilute Jay’s fluid and Cretaceous earth. This is to reduce the population of overwintering pests (especially any hibernating red spider-mites!)

March 2024 — With the peach in flower and green buds breaking, mid-March was the perfect time to undertake the corrective pruning to establish the correct alternating verticals. Unfortunately, this meant cutting out many flowering branches which, if left, would have produced peaches this year. However, in the long term, this thorough pruning was essential.

As explained in May-2023, I didn’t have an alternating pattern of shoots last year, so need to get it right this year. Also, some of the verticals (especially near the central section) are actually three or four year old wood. These have to come out, so that shoots are never more than two years old (i.e. new shoots grow from buds close to main horizontal stem in year 1, flower and fruit in year 2, then are cut back to a new bud to repeat the two year pattern in year 3/4)

Corrective Pruning

The above two photos show the drastic corrective pruning needed to get the alternating system of shoots on track, especially in the centre of the tree where there were three (or four?) year old branches and a lack of alternation.

In the right-hand image, you can see alternating vertical light and dark strings indicating the A/B years of growth. These show the desired position of the alternating (1) White string: last year’s growth which is now flowering (=this year’s fruit) vs (2) Dark string: spaces created for new buds to grow up.

Because the previous year’s growth was not yet in the desired alternating pattern (1-year old / 2-year old / 1-year old / 2-year old etc), I had insufficient 1-year old shoots to occupy all of the white strings. This time next year, I will have to treat some of the 1-year old shoots as 2-year old and cut them right back. But at that point, every string will have the correct-age vertical shoot on it. Hopefully, this long and complicated process will be worth while!

Next steps:

1. The task going forwards is to choose one strong new shoots to train up each of the bare strings. All other new shoots will be pruned back hard (some right back, others to a couple of inches*.
2. Side shoots on this year’s flowering verticals will be pinched back frequently so that there are just a few leaves to provide energy for the fruit.

* I have heard some people completely pinch off all unwanted buds at this stage (i.e. in March) instead of letting them grow into shoots at all, but I would be concerned that over time, there may not be sufficient active points for new buds production in the spring, as older wood will produce buds less freely. My thinking, therefore, is to always retain a few younger “spurs” towards the base of the verticals and along the main horizontal structure, that will more readily produce new vegetative buds.

MAY 2024

July 2024 – Harvest

We had plenty of fruit, but the flavour was not great. I think I need to stay on top of pruning better so the fruit is exposed to more sunlight. Also, I left a lot of them until they were ready to drop. Probably picking them a week or two earlier and letting them ripen inside would ensure they were better flavoured. I’ll also add wood ash around the base of the tree in case there is a potassium deficiency in the soil.

April 2025

Flowering in early march didn’t go quite as I expected. In theory, peaches fruit best on one year old wood (i.e. wood that grew in the previous season), however, on my tree some of my 1-year-old shoots produced just a few (or even no) flowers and hence limited fruitlets. Perhaps this is just a consequence of being in the middle of changing over to the new pruning regimen.

This spring (April 8th) I set about pruning as per the new regimen. This involved cutting back all of the 2 year old shoots, to a strong basal shoot which will replace it this year. Plus, removing most of the buds and side-shoots from the one year old canes carrying this year’s crop. The results are drastic, but should produce a better crop and be part of a more sustainable management system.

As you can see, the older (2 year old) shoots (occupying every-other vertical string) have been removed and fresh new shoots are being trained in near their base. The younger (1 year old) shoots in between have been retained and cleaned up. As last year was part of the transition period, not all of the new shoots were actually new (some older ones were kept to reserve their positions), and not all of the new shoots reached full height. Going forwards, this will be easier to achieve, as the growth from new shoots will easily reach the top of the wall this year.

The pictures above show how the alternate pruning method works. LEFT: Alternating fruiting with replacement shoots. RIGHT: Showing how one of the previous year’s fruiting shoots was cut back, removed and new shoots identified to replace it.

July 2025 – Spider Mites!

This year has been sunny, hot and very dry, with almost no rain since early April. Such weather provides perfect conditions for greenhouse spider mite. Unfortunately, I took my eye off the ball, and before I noticed what was happening, I had a serious infection:

In previous years, I have been able to cope with spider mite by applying just one round of biological control such as Amblyseius californicus early in the season as it tolerates low temperatures, or if I forget, Phytoseiulus persimilis later in summer as it prefers higher temperatures.

This year, I started with sachets of Amblyseius californicus but these, it turned out, were insufficient, possibly as it was too hot and dry for them to be effective.

I only spotted the issue when it was too late, and the infestation of spider mites was very advanced. A normal dose of predators would almost certainly fail to reverse such a serious infestation, so I took drastic action and removed 80% of the peach foliage (the most infected leaves), leaving only the most healthy (but still infected). Such radical action is necessary to give the predators a fighting chance. This is because infected foliage harbours lots of eggs which act as reservoir for new infestation, beating the predators which simply cannot reproduce fast enough.

Having stripped some stems bare, and others back to a minimum of foliage, I then introduced Phytoseiulus persimilis which were dusted on to the leaves from a tube. Yu can see the carrying medium on the leaves (top right). The stems that had been left bare recovered after a few weeks, putting out new growth. For a few weeks, new leaves were clear of spider mote, but by autumn, the spider mote had got a grip again.

You can see the ABC (Alternate Biennial Cordon) system in play here, with fruit growing on every other upright. This year, there are some without fruit, as they have not been through the proper 2-year cycle yet. Next year should be better.

When I pruned the shoots earlier in the year, I probably should have thinned the fruit more thoroughly. In many commercial systems, they will only allow one fruit per shoot (!) which ensures each fruit reaches a maximum size.

Harvest 2025

Removing so much foliage seemed, if anything, to benefit the ripening peaches allowing more light to reach them. This year has been a record for quantity and flavour, so no complaints there!

AUGUST 2025

Here, in August, after Harvest, you can see that the tree has recovered and there are lots of healthy leaves.

Unfortunately, by October, these again had become infested with spider-mite!!

More to come…

This post will be regularly updated as the peach tree develops and I train it further. Check back regularly!