The traditional practice in fruit thinning is to thin to either one or two fruits per flower cluster.
- On sites which regularly produce heavy crops of smallish fruits, thinning to single fruits per cluster is usually recommended.
- On more fertile sites, or with larger fruited varieties, thinning to two fruits per cluster is often preferred.
- Usually, this cluster thinning is combined with removal of all or most fruitlets on axillary wood.
Whilst this strategy of thinning is easy to explain to farm staff, it is rarely the best one for orchards.
- The abundance of flowering in trees varies from year to year and thinning to specific numbers of fruits/cluster may, therefore, result in very different crop loads per tree.
- Also, work in New Zealand has shown that it is better to leave two or even three fruits per cluster on ‘strong’ clusters and completely remove all fruits from other ‘weaker’ clusters.
- Similarly, strong floral buds on the one-year-old wood of varieties such as Gala can, on fertile sites with good tree growth, produce good fruit size and quality.
Ideally, growers should acquire an intuitive understanding of the type and size of crop which trees in particular orchards are capable of carrying and then thin accordingly. Unfortunately, this intuitive understanding is difficult to pass on to the casual labour often used for fruit thinning.
- Where possible growers should aim to thin trees to specified fruit numbers/tree (see above) rather than to specific numbers of fruits/flower cluster.
Optimum fruit numbers needed per tree in UK orchards
Trials and observations conducted by FAST in the UK have demonstrated the value of using thinning guidelines based on target numbers of fruits per tree at harvest.
- These target fruit numbers are adjusted to take account of the tree spacings within the rows or between rows in multi-row beds.
- Use the table below as a guide to fruit numbers per tree
- Better still using accurate grading records calculate the actual numbers per tree over the last three seasons and relate these to optimum yield and fruit size expectations.
Target numbers of fruits/tree at harvest to obtain optimum grade out
| Tree spacing | Target numbers of fruits/tree | ||||
|---|---|---|---|---|---|
| Cox & Discovery | Gala | Jonagored | Katy | Bramley | |
| 1-1.25 m | 80 | 96 | 95 | 70 | 40 |
| 1.5 m | 95 | 115 | 120 | 80 | 50 |
| 1.75-2 m | 110 | 125 | 130 | 100 | 60 |
| 2.5 m | 215 | 230 | 240 | 200 | 100 |
| 3.5-4 m | 420 | 460 | 475 | 400 | 200 |
- The above numbers of fruits are those required at the time of harvest and, if thinning is carried out prior to ‘June Drop’, extra fruit numbers will need to be left on the trees to compensate for this.
- For early thinning, approximately 10% to 20% more fruitlets should be left on the trees than shown in the above table.
Modern weight/size grading equipment will provide accurate weights of fruits and therefore fruits per kg for each size band. Where these are not available use the figures below as a guide
| Dessert Fruit | Bramley | ||
|---|---|---|---|
| Size | Kg | Size | Kg |
| <55 mm | 0.6 | <70 mm | 0.13 |
| 55-60 mm | 0.07 | 70-80 mm | 0.16 |
| 60-65 mm | 0.08 | 80-90mm | 0.22 |
| 65-70 mm | 0.10 | 90-100 mm | 0.27 |
| 70-75 | 0.13 | 100-110 mm | 0.37 |
| 75-80 mm | 0.16 | 110-120 mm | 0.45 |
| >80 mm | 0.20 | >120 mm | 0.50 |