Why does my plum tree flower but never fruit?

Plums are the earliest of the common tree fruits to flower, which is both what makes them charming in a cold March and what makes them unreliable. Cold, wet or windy weather during that fortnight keeps bees grounded even without a frost, and a single clear night below about -2°C ends the crop. The good news is that plums are naturally heavy croppers, so when conditions do work, they work very well.

Step by step

1. Check the blossom at flowering time.Open a flower and look at the centre. Blackened or brown centres with white petals means frost. If you do this once, in the year it happens, you save yourself years of guessing.
2. Assess the site for cold air.Cold air drains downhill and pools behind solid fences, walls and thick hedges. A plum at the bottom of a garden with a close-boarded fence below it is in the coldest spot available.
3. Check whether the weather was fit for bees.Cold, wet or windy conditions during flowering mean nothing flies. A perfect frost-free week that was 8°C and raining can produce the same empty tree as a frost.
4. Find out whether your variety is self-fertile.Victoria, Marjorie's Seedling, Czar and most damsons are self-fertile and can crop alone. Many gages, and varieties such as Jefferson and Coe's Golden Drop, need a compatible partner flowering at the same time.
5. Count the years.On Pixy expect fruit in three to four years, on St Julien A four to six. A plum grown from a stone can take a decade and may never be worth eating.
6. Think about last year's crop.Plums bear biennially quite readily, particularly Victoria. An enormous crop one year regularly means very little the next, and thinning hard in the heavy year evens it out.
7. Look for aphids and mealy plum aphid on the blossom and young leaves.Heavy infestation at flowering distorts growth and reduces set. Blast them off with water, encourage predators, and check for ants farming them.
8. Check the nitrogen and pruning.Heavy nitrogen and hard pruning both push a plum into growth instead of fruit. Plums need very little pruning — dead, damaged and crossing wood in summer, and no more.
9. Protect small trees on frosty nights.Fleece over a fan-trained or potted plum before dusk on a clear still night at blossom time, off again in the morning. On a full-size tree this is not practical and siting is the only lever.

Tips

• Victoria is self-fertile, reliable, and so widely planted that it is often the answer to 'what plum should I get' — but it is also markedly biennial and breaks its branches when it does crop.
• A plum against a north or west wall flowers later than one in the open and can dodge frosts that catch everything else.
• Late-flowering varieties, and damsons, are noticeably more reliable in cold gardens.
• If a plum sets heavily, thin it in June and prop the branches. Losing a limb in a good year sets the tree back for several.

Common mistakes

• Assuming a bare tree means it needs feeding — The commonest causes are frost and weather at flowering, neither of which is affected by fertiliser. Nitrogen makes an unfruitful tree grow more and fruit less.
• Pruning a shy plum hard to stimulate it — It responds with growth, and winter pruning risks silver leaf on top of it. Plums fruit better for being left largely alone.
• Planting a plum in the lowest, most enclosed corner of the garden — That is where cold air collects on the exact nights the blossom is vulnerable.

If it doesn't work

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