Gadenin日本語Get the appSelf-fertile in the main, but not uniformly so
Pomelo flowers carry both male and female parts and a good number of trees will set a usable crop entirely on their own. Pomelo is less reliably self-fertile than an orange or a lemon, though, and some trees are noticeably better with pollen from another citrus nearby. If your tree flowers heavily every year and sets almost nothing, and you have ruled out the weather and the drop pattern described below, a second flowering citrus within bee range is the practical fix.
Pollen moves on insects, mainly bees, over quite short distances. Another citrus within about fifty feet (15 m) and flowering at the same time is enough; you do not need it adjacent. The flowering windows of citrus overlap widely, so almost any other citrus in the neighborhood will do the job, including one in a pot on a terrace or in a garden two doors down.
The other consequence of cross-pollination is worth knowing before you arrange it. Pollen from another citrus tends to produce more seeds in the resulting fruit. In a pomelo, where you are already dealing with a great deal of pith, extra seeds make the eating harder work. If your tree already sets adequately on its own, leave it alone rather than adding a pollinator for its own sake.
Weather stops pollination more often than partners do
Citrus pollen is inactive when it is cold and it clumps and fails when it is soaked. Bees stop flying below about 55F (13C) and in rain or strong wind. A flowering period that runs cold and wet will produce a poor set on a perfectly healthy, perfectly self-fertile tree, and this is by far the most common explanation for a year with flowers and no fruit.
Heat cuts the other way. Above about 95F (35C) the stigma dries too fast for a pollen grain to germinate on it, and a hot dry spell landing squarely on full flower will strip a set just as thoroughly as a cold one. Both of these are single-season problems. A tree that failed in a bad flowering week is not a failing tree, and the wrong response is to prune or feed it hard in reaction.
Water matters more during flowering than at any other point in the year except the final swell. A tree that goes dry while in flower and just after will abort young fruit wholesale, and gardeners routinely read that as failed pollination. Keep the soil evenly moist from the first open flower until the fruitlets are the size of a walnut, and you will have removed the most common cause of what looks like a pollination failure.
| Condition during flowering | Effect on set | What to do |
|---|---|---|
| Below 55F (13C) | Bees do not fly; pollen inactive | Wait; hand pollinate the flowers that open in warm spells |
| Steady rain at full flower | Pollen clumps and washes off | Nothing outdoors; move a container tree under cover |
| Above 95F (35C) and dry | Stigma dries before germination | Shade cloth at midday and keep the soil moist |
| Dry soil at flowering | Heavy abortion of young fruitlets | Even watering from first flower to walnut size |
| Warm, still, 65-85F (18-29C) | Ideal; bees active and pollen viable | Leave the tree alone and avoid spraying |
| Insecticide sprayed on open flowers | Pollinators killed or driven off | Never spray a citrus in flower; wait until petal fall |
Hand pollination when the weather will not cooperate
Hand pollination is worth the trouble for a container pomelo kept under cover, for a tree flowering in a cold spell, or for a young tree where you want a small number of fruit to set reliably rather than a large number to set and drop. It takes a couple of minutes a day over the flowering week and it is genuinely effective.
Work in the middle of a warm dry morning, when the pollen is loose and the stigma is receptive. The stigma is the sticky knob at the center of the flower; the anthers are the ring of yellow-tipped stalks around it. You are simply moving grains from one to the other, and the flower is large enough that you can see exactly what you are doing without a lens.
- Pick your moment Mid morning on a warm dry day, once the dew has gone. Pollen is loose then and the stigma is at its most receptive. Flowers open over a week or more, so plan on repeating this for several days rather than doing it once.
- Collect pollen Twist a small soft brush or a cotton bud gently against the anthers of a freshly opened flower until the tip is dusted yellow. If no yellow transfers, that flower is either too young or already spent; move to another.
- Touch it to the stigma Dab the loaded brush lightly onto the sticky central knob of the flower you want to set. A light touch is enough; you are not painting it. Use pollen from a different flower where you can, and from a different citrus if you have one.
- Mark what you treated Loop a short piece of soft wool round the stalk of each pollinated flower. In three weeks you can see plainly whether your treated flowers set better than the untreated ones, which tells you whether to bother again next year.
- Do only as many as the tree should carry On a young or lightly built tree, pollinate a handful of flowers on strong well-placed branches rather than everything in reach. Fruit you set deliberately in the right position is worth more than fruit the tree will shed anyway.
Fruit drop is normal, and the second drop is the tree deciding
A pomelo sets far more fruitlets than it can finish and sheds the surplus in two waves. The first comes within days of petal fall and is simply the unpollinated flowers letting go; it looks alarming because the ground is covered, but it costs you nothing. The second wave comes weeks later, when the fruitlets are somewhere between pea and walnut size, and this is the tree matching its load to its resources.
That second drop deserves respect rather than panic. On a pomelo, where a single finished fruit can weigh two to four pounds (1-2 kg), a tree that kept everything it set would break its own branches. If the drop is severe on a mature tree, look at water first, then at a cold or hot snap during flowering, then at a heavy crop the previous year. Reaching for fertilizer is almost never the answer and a nitrogen surge during the drop can make it worse.
What you should do is finish the job the tree started. Once the second drop has run its course, thin the remaining fruit yourself so that no branch is carrying more weight than it can hold and no two fruit are touching. Thinning is covered in detail under harvest and pruning, but the decision belongs to this stage of the year, when the fruit are still small enough that removing them costs the tree almost nothing.
Keep a simple record each year of the date the first flower opened, the weather across that week, and roughly how many fruit were still hanging a month after petal fall. Three seasons of that turns the annual panic about fruit drop into a number you can compare, and it usually shows the weather explaining most of the variation.