UFO training of sweet cherries

Cherries are typically rather vigorous trees with an upright growth habit. They can therefore be challenging to develop in restricted forms suitable for the kitchen garden. A sour cherry is naturally more dwarfing than a sweet cherry and may make a reasonable fan against a wall or fence of some six feet in height. A sweet cherry, though, can be difficult to contain. Until relatively recently, Colt was the main somewhat dwarfing rootstock; it is still semi vigorous and a fan on Colt, in reasonable soil, is likely to put forth rather too much strong vegetative growth. More recent rootstocks, such as the Gisela series, are more dwarfing and allow cherries to be grown in more compact forms.

Our new fruit cage is based on our old polytunnel frame. It is much smaller than our previous fruit cage and has little room for fan trained fruit; there is, perhaps, enough space for one tree at the end, but I would like to plant a number of different varieties of sweet cherry in there. I could plant around our new fence, but I already have plans for sour cherry and plum fans for that, and it would be nice to have the sweet cherries in the fruit cage where birds can be readily excluded. For that purpose, a restricted form is needed. Whilst amateur gardeners such as myself typically look to one of a handful of tree forms – bushes, half-standards, cordons, espaliers, fans, etc. – modern commercial orchards explore a wider range of pruning and training regimes, typically based on high density plantings on dwarfing rootstocks. It is from that domain that I came across the UFO approach. UFO is short for Upright Fruiting Offshoots, and is a fair, if not entirely clear, descriptor.

Planting UFO sweet cherries in the fruit cage

The UFO approach relies of a precocious dwarfing rootstock; Gisela 5 is the most readily available of such rootstocks and probably well suited so that is what we have chosen. Precocity is of importance as bearing fruit will reduce the vigour of vegetative growth and the sooner that happens the better. The growth habit of the sweet cherry is typically upright and that can be awkward when fan training. Rather than attempt to curb that upright habit, UFO cherries exploit it to produce what is, effectively, a fruiting wall of cherries. One might typically expect a UFO cherry to be eight to ten feet in height. In our fruit cage I have closer to six feet, so it will be interesting to see how this method may be adapted to such tight spaces.

The first step in developing a UFO is to plant the tree at an angle, much like an oblique cordon, perhaps around 45 degrees (Fig 1). The main stem is then laid down towards the horizontal. The objective is to produce a low, fairly straight main stem that fills the available width. In our case we have about eight feet between trees so we do need to extend the main stem a fair bit on the young trees we have planted. Laying down a stem greatly reduces vigour. It may be may be done straight away or gradually over time. In our case we will probably lay it down only part way until a suitable length of extension growth has been produced. Hopefully we only need one season to develop this.

Fig 1. Typical situation on planting. (1) main stem planted at around 45 degrees (2) graft union located uppermost (3) poorly place lateral that will be cut out after bud break (4) well placed lateral that may be retained

All shoots arising from the main stem that are not more or less vertical are removed, so there is no growth underneath or to the sides. If planting a feathered tree, which is quite likely with cherries, most laterals will need to be removed, but not until after bud break in the spring. Thereafter, the intention is to produce evenly spaced upright shoots that will bear the fruit (Fig 2). By having an array of vertical growth, the vigour of the tree is distributed amongst all the shoots rather than having just one or two leaders taking control.

Fig 2. UFO cherry in development (new growth in green). (1) main stem laid down towards the horizontal (2) extension growth that will be laid down to complete the main stem (3) new upright shoots to form the fruiting wood

Ideally, all shoots will be of a similar diameter. If a particular upright shoot becomes too vigorous it can be cut back to a stub, which should then regrow one or more new shoots of less vigour (Fig 3 and 4). Two could be kept if the space allows, or then they can be back to just one. In that way, a reasonable balance can be maintained amongst the upright shoots. A mature tree, with an array of fruiting wood, will need some renewal as the productivity of old wood diminishes. Maintenance is a process of cutting back a portion of the older wood each season, shortly after bud break, to promote renewal. Sub laterals – that is, side shoots arising from the vertical stems – are typically cut back, either completely or leaving a short stub. Cherries fruit at the base of one year old wood as well as on short spurs on older wood, so the stubs can be left until after fruiting in order to secure the cluster of cherries that may well form there and cut out after.

Fig 3. Treatment of overly vigorous shoots. (1) vigorous shoot (2) cutting point (in red)
Fig 4. Less vigorous regrowth (in green) following pruning

The UFO approach seems to have a number of advantages. It is fairly compact and pruning and training is a relatively simple and quick affair. The main challenge here will be whether our restricted space is sufficient for this sort of tree; we probably have about the right width, but the height is a little tight. It will be interesting to see how the trees develop and whether we can manage to keep them contained. The young trees may be on Gisela 5, but they look like robust specimens, as one might expect for well grown sweet cherries.

We put together five old varieties that should cross pollinate effectively, being in favourable pollination groups and having a mix of incompatibility groups. Widespread incompatibilities within the cherries – at least the old sorts that are not self compatible – mean that some care is needed when selecting varieties. We chose the following:

Early Rivers, which, as the name suggests, is an early sort, one of the first to ripen, raised by Thomas Rivers. Robert Hogg records that it first fruited in 1869.

Noir de Guben is a large fruited dark cherry from Germany. The youngster of this collection, it dates back to the late 1800s.

Waterloo is one of numerous cherries from the orchard of Thomas Andrew Knight, possibly from a Biggarreau pollinated by a May Duke. It is said to have first cropped just after the battle of Waterloo, 1815.

Amber, also known as Kent Bigarreau or Amber Heart, is an old variety from Kent, one of the so-called white cherries. Not really white, of course, such cherries are a pale yellow to golden colour, with some crimson flushing and darker colour on well exposed fruit. They are most attractive and have a slightly different flavour from the more usual red cherries. There were once many varieties of white cherry in use, but now they are much less common.

Roundel is a dark red fleshed and large fruited cherry of uncertain origin. Taylor speculates that it may be an older variety under a different name. It may date back to the late eighteenth or early nineteenth century.

Tying the first cherry, Early Rivers, in position just prior to planting

This planting of cherries is an experiment and time will tell whether or not we can grow them in this way in the space available. I hope so, as they are probably my favourite fruit. If vigour is successfully contained, the UFO approach should be easier to manage than a fan, which is the typical form for a cherry in the kitchen garden.

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