Gadenin日本語Get the appMost almonds cannot pollinate themselves
The usual reason a healthy almond flowers heavily and sets nothing is not frost and not feeding. It is that the tree has no source of compatible pollen. Most almonds are self-incompatible, which means the tree rejects its own pollen and the pollen of anything closely related to it, and no amount of bees will change that. It needs pollen from a genetically different almond, carried by an insect, onto its open flowers.
A minority of almonds are self-fertile and will set a crop standing alone. If you know your tree is one of those, one tree is enough, though even a self-fertile almond sets more heavily with a partner nearby. If you do not know, assume it is not, because a self-incompatible tree planted alone will flower every spring for its whole life and never give you a nut.
The distance matters less than people think, but it is not unlimited. Two trees within 50 feet (15 m) of each other, with nothing solid in between, will be worked by the same bees. Beyond about 100 feet (30 m) the transfer gets thin, and a wall or a building between them makes it worse than the distance alone suggests.
| Situation | Will it set a crop? | What to do |
|---|---|---|
| One self-incompatible tree alone | No, or almost none | Plant a second, different almond within 50 feet (15 m), or graft a second variety into the tree |
| Two different almonds, overlapping bloom | Yes, this is the normal arrangement | Nothing; make sure both flower at the same time and both are reachable by insects |
| Two trees of the same variety | No | They share the same incompatibility; a second variety is needed, not a second tree |
| One self-fertile tree alone | Yes, but lightly | Hand-pollinate in still weather, or add a partner to lift the set |
| A tree under a rain cover | Poorly, insects cannot find it | Hand-pollinate every other day while flowers are open, or open the sides of the cover in fine weather |
The flowering windows have to overlap
Having two different almonds is not enough on its own. They have to be in flower at the same time, because pollen has to move from an open flower on one tree to a receptive flower on the other. Almond varieties differ by two or three weeks in when they open, and in a warm early spring those differences stretch rather than compress.
An almond flower is receptive for a short time, usually about three to five days from opening, and less in hot or windy weather. That means you need a real overlap of a week or more, not two trees that just catch each other's last and first days.
This is the single most useful thing to record. Write down the date the first flowers opened and the date the last petals fell on each tree, every year. After two seasons you will know whether your pair genuinely overlaps, and if they do not, you can fix it by grafting a branch of a third variety into one of the trees rather than by planting and waiting another five years.
If you have only one tree and no room for another, graft two or three shoots of a different almond into the framework of the tree you have. A single grafted limb, once it flowers, supplies enough pollen for the whole tree, and the bees do not have to travel at all.
Almonds flower when there are hardly any insects flying
This is the practical problem behind almond pollination in a garden. The tree opens its flowers in the coldest part of the season, when honeybees are barely active and many wild bees have not emerged. Bees do very little flying below about 55F (13C), and almost nothing in wind or rain, so a week of cold wet weather across the flowering period can cost the entire crop even where the pollination arrangement is perfect.
You cannot make it warmer, but you can make the little warmth there is go further. A tree in a sheltered sunny corner is several degrees warmer at midday than one standing in the open wind, and those degrees are the difference between bees working the flowers and bees staying at home.
Wild bees matter more than honeybees at this time of year, because several kinds fly at lower temperatures and in duller weather. Leave some bare, undisturbed soil and some hollow dead stems near the tree, and stop tidying every corner of the garden in autumn. Anything flowering at the same time as the almond helps too, because it gives early insects a reason to be in that part of the garden at all.
- Shelter the flowering tree from wind A hedge, fence or wall on the windward side raises the temperature in the canopy and lets insects work. Wind is a bigger obstacle to early pollination than cold air on its own.
- Leave nesting habitat close by Bare sunny soil, an old wall, hollow stems and a rough corner left uncut give solitary bees somewhere to be. They emerge earlier than honeybees and work in cooler, duller weather.
- Do not spray anything while flowers are open Insecticide applied during bloom kills the pollinators you are depending on, and there is nothing you would be treating at that stage that cannot wait until petal fall.
- Give them something else to visit Early-flowering bulbs, willows and winter-flowering shrubs near the tree pull insects into that part of the garden during the almond's narrow window.
- Watch the weather across bloom If the forecast is cold and wet for the whole flowering period, plan to hand-pollinate. It is the only reliable answer when insects simply are not flying.
Hand-pollinating, and how to store pollen
Hand-pollinating an almond is straightforward and takes about ten minutes twice a week through the flowering period. It is worth doing on a covered tree, a potted tree under shelter, a single self-fertile tree, or in any spring where the weather keeps the insects grounded.
Work in the middle of a dry day, when the flowers are fully open and the pollen is loose. Use a soft artist's brush, and move from the flowers of one variety to the flowers of the other, not back and forth at random. Touch the center of each open flower lightly. You are transferring dust, not scrubbing.
Where the two trees do not overlap in bloom, collect pollen from the earlier tree and hold it for the later one. Pick flowers that have just opened, shake the pollen into a small dry container, and keep it in a closed jar in the coldest part of a refrigerator. It stays usable for a couple of weeks, which is usually enough to bridge the gap between two badly matched trees.
Repeat every other day while there are new flowers opening. One session catches only the flowers that happened to be open on the day, and an almond opens its flowers over one to two weeks.
Flowers that set and then drop
Not every pollinated flower becomes a nut, and an almond sheds a proportion of what it sets a few weeks after flowering. That is normal. What is not normal is a tree that goes from full bloom to bare in a matter of days.
If the petals brown and the whole flower turns to mush and drops within a day or two of a cold night, that is frost, not pollination, and the two are easy to confuse. Cut one open: a frosted flower has a blackened center. Two layers of row cover thrown over a small tree in the late afternoon and removed in the morning is enough to save a marginal night, and watering dry soil in the afternoon helps a little because wet ground releases more heat overnight.
If the flowers hold, go over, wither slowly and drop over two or three weeks with no swelling at the base, that is failed pollination. Record which it was, along with the flowering dates and the weather across the bloom, and after two or three seasons you will know whether your problem is the arrangement of trees or the climate, which are fixed in completely different ways.