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Almond Bloom: How A Flower Turns Into A Nut

Sarah Bohannon
North State Public Radio
An almond flower in bloom at Chico State's University Farm.

Almond bloom in the valley seems to have left as quickly as it came. That eye-catching sea of white flowers that every almond tree in the North State had on display a few weeks ago is now mostly on the ground – surrounding the trees’ trunks like snow. But what exactly has been happening in the orchards for the last few weeks while the trees were in bloom?

One word: pollination.

Credit Sarah Bohannon / North State Public Radio
North State Public Radio
Chico State agriculture professor, Rich Rosecrance examines some almond blossoms at the University Farm.

Now it’s important to remember that almond trees are self-infertile. That means they have to cross-pollinate with other trees in order to grow almonds.

But when you’re a tree deeply rooted in the ground, how can you make cross-pollination happen? I mean, you can’t just walk over and swap pollen with another tree. You need something to carry it for you. In this case, a bee. A bee with a furry little body that attracts pollen like a black shirt does lint. 

It all depends on the weather, but almond pollination normally happens somewhere between January and February. Agriculture professor of fruit and nut production at Chico State, Rich Rosecrance, said that during pollination bees act as sort of unknowing pollen traffickers moving pollen from bloom to bloom.

“In the process of getting nectar they get pollen attached to their bodies –attached to their legs, sometimes right on their body because they have very hairy bodies, and then they go to another tree and hopefully it will land and it will touch the stigma,” he said.

The stigma is the female part of the flower. If the pollen touches that then there’s a chance fertilization will occur. But even then, a lot still has to happen.

First, the pollen dropped has to have different genetics than the flower it’s on. If the genetics are different, then the pollen next has to germinate and grow down into a small tube in the center of the flower to get to the flower’s ovule.  

“So it is a very complicated process and so you can imagine why an almond — typically only 30 percent of the flowers set fruit,” Rosecrance said.  

Credit Sarah Bohannon / North State Public Radio
North State Public Radio
Chico State agriculture professor, Rich Rosecrance stands near some bee boxes that house bees that are being used for almond pollination at the University Farm.

The reason only 30 percent of the flowers on an almond tree turn into a nut is that everything has to line up perfectly – and all around one short-lived timeframe, Rosecrance said. It’s called the “effective pollination period,” and is the one to three days that an almond flower is receptive to pollen. If the flower doesn’t get pollinated during this time then the farmer can say goodbye to the bloom ever becoming an almond. 

This is why bees are so important to the million-acre California almond industry, and why this year farmers paid up to five times more to rent them for their orchards than they did ten years ago. In terms of yield, bees play a big role in making or breaking a crop, Rosecrance said.  

“One of the tightest correlations is the number of hours that bees fly during the pollination period,” he said. “So the longer the bees are flying in the orchard, the higher the set and the higher the yield.”

Almond farmers won’t be able to tell how busy those bees were this year until they start seeing almonds on the trees. But if she had to guess, Dani Lightle would deduct pollination went well. Lightle is an orchard systems advisor for the UC Cooperative Extension and she covers Glenn, Butte, and Tehama counties. This year’s sunny and warm weather should be in the almond farmers’ favor, she said. 

Credit Sarah Bohannon / North State Public Radio
North State Public Radio
Chico State agriculture professor, Rich Rosecrance points to the female part of the almond flower called the "stigma." Pollen from an almond flower has to be carried to the stigma of a flower with different genetics in order for it to be fertilized and turn into an almond.

You see, while to the untrained eye almond trees in an orchard all look the same, they’re not. They alternate between different varieties. They’re usually planted in a way that maximizes the pollination of the industry’s most valuable variety: nonpareil. It often accounts for about 50 percent of an orchard and is planted so that it stands between both an early and late blooming type. When you have warm weather like the North State experienced in early February, it can trigger all varieties – early, middle and late bloomers – to flower at once, Lightle said.

“And that’s actually really good for pollination too because some years the bloom is really spread out and you could have pollinator varieties bloom and be done blooming when nonpareil blooms, and then you don’t have good overlap,” she said.

Not having good overlap could mean not having good cross-pollination, and as we already know almond production depends on cross-pollination. So although we didn’t get to enjoy the beauty of this year’s blooms for long, their short-lived exhibition should be a good sign for farmers because it “tends to make for good pollination events,” Lightle said. 

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