Prune Plum Year: Season by Season from Blossom to the Drying Racks

The shape of the year

There are four decisions in a prune year and everything else is routine. Whether to protect the blossom on a cold night. How hard to thin in early summer. When to stop watering. And when to pick, or to strip the tree ahead of rain. Get those four right and the rest of the work is walking the tree regularly and keeping the ground clear.

The calendar below runs by season rather than by date, so it reads the same in either hemisphere. Adjust it to your own site using your blossom record, which is a far better guide to where you are in the sequence than any generic timetable.

Late winter and blossom: protect what sets the whole year

The dormant season is a season of not doing things to a prune tree. No pruning of any kind, because wounds made now stay open through the whole silver leaf spore season. The only useful jobs are checking that stakes and ties have not started to bite into thickening bark, removing any mummified fruit still hanging that you missed, and clearing fallen fruit and leaves from under the canopy so the ground is clean going into spring.

Feed only if the evidence says to. Measure last season's shoot extension at a few branch tips: twelve to eighteen inches (30 to 45 cm) on a bearing tree is right and needs nothing. Under eight inches (20 cm) is genuinely short and justifies a balanced feed spread over the rooting area in late winter, before growth starts. A potassium feed is worth it on light soils regardless, because potassium is directly tied to fruit sugar.

Then comes the one genuinely anxious week of the year. These trees blossom early, and a hard frost at full bloom removes the crop outright. On a small or trained tree, throwing row cover or an old sheet over it on a clear still night with a frost forecast is worth doing, put on at dusk and taken off in the morning. On a large tree it is impractical and the site has to do the work instead, which is why the tree was planted above the frost pocket in the first place. Record the bloom dates every year; after a few seasons you will know your own risk window precisely.

Petal fall to midsummer: the jobs that decide the crop

This is the working part of the year, and everything done in these weeks shows up in the sugar level of the fruit three or four months later. Nothing here can be caught up on afterwards.

1. Wait out the natural drop The tree sheds a large proportion of the set fruit itself, a few weeks after petal fall. Do not thin before that has finished or you will end up with far too little. Assess the load once the drop has stopped.
2. Thin to one fruit every three to four inches When the remaining fruit is about hazelnut sized, thin to one every 3 to 4 inches (8 to 10 cm) along the branch. Take damaged and marked fruit first, then space out the rest. It looks severe and it is the single biggest lever on final sugar.
3. Rub out watershoots while they are soft Strong vertical shoots on the tops of main limbs shade the fruit below them all season. Remove them with your thumb in early summer, when they come away without a cut and leave no wound.
4. Water deeply while the fruit expands Fruit size is decided in this window and cannot be recovered later. Keep the soil evenly moist to a foot (30 cm) deep with occasional heavy soaks rather than frequent light sprinkling.
5. Prop every limb that is starting to bend A prune tree carries its crop for weeks longer than other plums, including through autumn wind. Put forked props under bending limbs, or tie them to higher branches, before the fruit finishes coloring.
6. Clear the ground and keep it clear Mow under the canopy and pick up every dropped fruit, including the sawfly-damaged ones with a sticky hole in them. Fruit left lying is how brown rot and wasps get established for the rest of the season.

Late summer: the long hang, and the twice-weekly walk

At some point in late summer the fruit reaches full color and looks ready. This is the moment that separates a prune from a dessert plum, because you now leave it alone. Sugar keeps building for weeks after color, and the fruit is not ready until it softens right through, wrinkles finely at the stem end, and releases the stone cleanly. Picking at color gives you a decent plum and a batch of dried fruit that sours around the stone.

Taper the water off as the color comes. A slight deficit through the final weeks concentrates the flesh and, more importantly, means the tree is not already full of water when rain arrives. That is what determines whether the crop splits. From this point, watering is something you do only if leaves are still limp at dawn.

The routine through these weeks is the twice-weekly walk. Ten minutes, twice a week, taking off any fruit that has split, browned or gone soft in a patch, and picking up everything that has fallen. Take it all out of the garden. This is unglamorous and it is the difference between a crop and a canopy of brown rot, because the fungus spreads fruit to fruit and the whole strategy of this tree is to keep ripe fruit hanging for as long as possible.

Keep an eye on the forecast the entire time. Once fine wrinkles appear at the stem, a wet spell coming is a reason to pick everything that gives at all, ahead of schedule. Fruit slightly short of perfect, picked dry, dries well. Perfect fruit picked after a soaking often does not.

Harvest into autumn: picking rounds, drying, and closing the year

Picking runs over three to five weeks and eight to twelve rounds, because ripeness moves through the tree from the sunny outside inwards. Each round, take only fruit that lifts away with a light twist, sort it as you go into fruit for drying, damaged fruit for immediate cooking, and rot for removal, and dry in batches rather than waiting for a full crop. Drying whole needs either a genuine run of hot dry weather with air moving under single-layer racks, or a dehydrator at 135 to 145F (57 to 63C) for eighteen to thirty-six hours.

Once the last fruit is off, the summer pruning window is open and it is the best one of the year, because you can still see exactly which wood carried and which sat idle in the shade. Take out no more than about a fifth of the canopy: dead and damaged wood first, then every mummified fruit still hanging, then crossing and inward branches, and finally enough of the middle that you can see patches of sky when you stand underneath. Give the tree one deep soak afterwards to recharge it for next year's buds.

Then stop. From leaf fall through the dormant season, do not cut anything. Clear the ground under the tree thoroughly, because fallen fruit and mummies left over winter are the starting inoculum for next season's brown rot, and renew the mulch, keeping it clear of the trunk. That is the whole of the winter work.

Close the year by writing up the record while it is fresh. Bloom dates, the date thinning finished and how many fruit you left, the date you stopped watering, first and last picking dates, and a short failure log: how much split and after which rain, how much rotted, how much soured on the rack. Add the end-of-season shoot extension measurement. Six lines, once a year, and within three seasons you have a document that tells you more about your own tree than any general guidance can.

Photograph the tree from a fixed spot immediately after the summer pruning, every year. Set side by side, those pictures reveal a canopy slowly closing in, which is the drift that quietly costs you sugar, and they show it long before you would notice it standing in front of the tree.