The Niab Plum Demonstration Centre (PDC) operated between 2015-2025. Here we summarise the key findings in pruning and tree management.
A more recently planted orchard including Victoria, Malling Elizabeth (formerly P7-38) and the early Malling selection P6-19, all on Wavit rootstock, was established at a closer row spacing so it could be covered by polytunnels. A total of eight rows (four Victoria, two Malling Elizabeth, two P6-19) were covered with four tunnel bays. Originally designed to demonstrate the benefits of protecting plums on fruit quality, the consortium has preferred to use it to compare pruning techniques and more efficient sensor-driven irrigation scheduling techniques.
All eight rows are supported on a post and wire system and trained as a hedgerow. In the early years after establishment, the trees grew very strongly so the consortium worked with NIAB farm manager Luis Felgueiras to reduce the vigour using a combination of hand pruning in May and root pruning, which was carried out in February before bud break.
In seeking to reduce tree management costs using hand labour, the consortium compared the impact of hand pruning in late spring (May) with mechanical pruning of the sides and tops of the canopy above the top support wire. In 2022, this mechanical hedge pruning was carried out on a single row of Victoria in the second week of July following the longest day, and this stopped all growth for the remainder of the year.
In 2023, this row had the most balanced growth, best fruit set, and highest marketable yield of all the rows in this orchard. The other rows had been left unpruned until May 2023, when hand pruning aimed to reduce tree height to the top wire, remove upright and over-vigorous growth, remove bare unproductive wood, tie down branches where appropriate, and return the rows to an A-shape where the tree structure had been lost.
In 2023, the same Victoria row was pruned mechanically after harvest, whilst pruning of the other rows was delayed until May 2024. By summer 2024, although the growth of the mechanically pruned row was balanced, there was less fruit set, particularly lower in the canopy. In contrast, the hand pruned trees had a better set of fruit, primarily forming on the outer canopy which had formed during the 2023 season.
This demonstrated that although hedge pruning the outer canopy saves on labour costs, if insufficient new growth has formed in the centre of the canopy, growers run the risk of reducing yield potential. The consortium agreed that where hedge pruning is used in future, hand thinning unproductive wood between trees in the crop row is essential to encourage the development of new fruiting wood.
In 2023, the new variety Malling Elizabeth had become over-vigorous, but following root pruning in February 2024, tree vigour was significantly reduced and gave rise to a much more open canopy with better light interception. The fruit set was rather light, but the best fruit was found on wood that was growing at a horizontal angle rather than on more up-right vigorous growth.
Key findings
Rootstock/Tree Architecture Irrigation Variety Trial
The Plum Best Practice Guide
The Guide brings together information on plum production into one place and develop from that information recommendations for best practice in the UK.