Thinning should occur roughly around the same time as ‘reference date’, or the point at which 80-90% of the fruit have a visible endosperm. The endosperm, a clear gel-like glob, will be found in the seed on the blossom end of the prune and is solid enough to be removed with a knife point. Typically, the reference date occurs in late April or early May, approximately one week after the pit tip begins to harden. The earlier the thinning is done, the greater effect it will have on final fruit size at harvest, though if you thin too early, you may damage the trees without removing the desired number of fruit.
Read more about thinning and the logic behind the calculations here.
To decide whether to thin, follow the steps in the calculator below. The calculator will perform the math and aid in your decision of whether and how much to thin.
Cells highlighted in yellow are editable and can be filled with your orchard specific data.
| Step 1. Estimate the targeted tonnage from a given block by considering orchard history, age, etc. | |||
| Targeted yield (dry pounds/ ac): | |||
| Targeted count (dry count/ lb) | |||
| Trees/ acre | |||
| Target fruit / tree at harvest: | 0 | ||
| Step 2. Determine the actual number of fruit in a sample tree and compare that number to the target (calculated above). Ideally, you would repeat this procedure on 3 trees, representative of most trees in the orchard, to ensure accuracy. Place a tarp under the tree and mechanically shake off as much fruit as possible, then hand strip any remaining fruit. Collect all the sound fruit from the tarp and weigh them. Take a 1-lb subsample of the fruit and count how many sound fruit are in a pound. Don’t count fruit that looks like it wouldn’t have stayed on the tree (if you hadn’t have stripped it off). These fruit are light green or otherwise look slightly “off” compared to the strong fruit that will make it to harvest. | |||
| Total tree fruit weight: | |||
| Number prunes/lbs: | |||
| Total number of fruit/tree: | 0 | ||
| Step 3. Decide if you need to thin. | |||
| Target number prunes/tree | 0 | ||
| Total number fruit/tree | 0 | ||
| Difference: | 0 | ||
| Step 4. Account for natural fruit drop and variability in fruit/tree across the orchard. Estimates of natural fruit drop range from 10%-40%. Account for your orchard history, as well as your own risk threshold. Many growers prefer to leave approximately 50% more fruit on the tree than the target amount. | |||
| Fruit drop buffer (%) | |||
| Adjusted target number fruit/tree: | 0 | ||
| Step 5. Calculate how many fruit to remove. | |||
| Actual fruit/tree: | 0 | ||
| Adjusted target number fruit/ tree: | 0 | ||
| Number fruit to remove: | 0 | ||
| Step 6: Determine how long to shake. Shake a tree for one second, and count how many fruit were removed. If needed, increase the shaking time until the desired numbers are removed. Typical shaking time is 2-4 seconds; avoid shaking for longer than 6-7 seconds to prevent unnecessary damage. Once you’ve calibrated your shaking time, go through and thin the block. If you are thinning for more than a week, check fruit per tree and green fruit per pound every few days to make sure that your shake time doesn’t need to be adjusted down as fruit grow. | |||
| Target number fruit to remove: | 0 | Target number fruit/tree at harvest: | 0 |
| Fruit removed from 1-second shake: | Fruit remaining after 1-second shake: | 0 | |
| Fruit removed from 2-second shake: | Fruit remaining after 2-second shake: | 0 | |
| Fruit removed from 3-second shake: | Fruit remaining after 3-second shake: | 0 | |
| Fruit removed from 4-second shake: | Fruit remaining after 4-second shake: | 0 | |
Leave a Reply