Evaluating squash pollination
A critical, but often overlooked or misunderstood part of growing squash is pollination. Some folks have a vague notion that bees are good – that bees have to visit the squash blossoms – and they assume bees will come.
In these days of pollinator decline, this is not a valid assumption. To grow squash sucessfully, one must ensure good pollination. And pollination is not just an on/off switch, where a bee just visits the flower and pollination is accomplished.
Pollination is a progressive thing with any multi-seeded fruit. You can have many stages, from no pollination at all, to full pollination. This is because many grains of pollen must be delivered to the sticky stigma of the female flower – two pollen grains for each incipient seed. And these pollen grains must be evenly spread across the surface of the stigma.
The perfect squash in the photo above results from almost every incipient seed being fertilized. The act of fertilization stimulates the development of the flesh of the fruit.
Female squash blossoms have an ovary – the incipient fruit – at the base of the flower. If no pollen grains are delivered, the ovary will simply shrivel and dry up. If you touch it, it will fall off.
But, if a few grains are delivered, the fruit may actually start to grow. This fools some people into thinking that it’s pollinated.
The fruit will stop growing, shrivel up and often rot at the blossom end. This is not blossom end rot. Blossom end rot is a calcium metabolism problem; it shows up in fully-formed fruit; and it is much more common in tomatoes than squash.
There is a fungus involved here, but it is opportunistic; no amount of fungicide will prevent this fruit from aborting.
Zucchini (courgette) and other squashes all will exhibit the same kind of response to inadequate pollination.
Let’s suppose a few more incipient seeds are fertilized, but still nowhere near the full quota of seeds. This is what you get:
The fruit may actually size up somewhat, but it still will be wrinkled and poor quality. It will also grow much slower than a well pollinated fruit.
The poorly pollinated squash on the top is actually 2 days older than the well pollinated one on the bottom.
When I was in the pollination business, a farmer called me. He was just about in tears. He had planted 75 acres of yellow squash for market. During the winter, he had given me an order for bees to place on the fields, and he gave me the date he expected to need them. But he planted his squash much earlier than planned – taking a risk with frost – but he figured he’d win big if he had the first on the market.
Unfortunately he forgot to call and tell me he needed the bees earlier. Now his harvest crew was on the first picking, and they were throwing away almost the entire picking. They looked just like the upper squash in the above photo. I went straight to his farm that morning, and bees were notably absent from his fields.
The bees were delivered that night, and the rest of his harvest was very good. The problem: The day of the first picking, there was very little squash on the market – and it was bringing $18 a box. If he’d had a normal picking, it would have brought a small fortune. But the price dropped rapidly, and by the fourth picking only brought him $4 per box. There was no 5th picking, as the market price of $2 a box would not pay the picking cost.
The lesson is clear: we need to pay much more attention to the bees. Pollination is a critical part of growing squash, whether for the garden or the farm. And commercial growers cannot assume wild bees will do the job!
Pollination failure can occasionally happen from a rainy day. In small plantings, you sometimes have crazy plants that have all female and no male flowers. And extreme heat can kill squash pollen. So there are other possible reasons for pollination failure. But persistent pollination problems usually stem from a lack of bees.
In an upcoming post, we’ll talk about the kinds of bees that do squash pollination.
This entry was posted on Wednesday, June 15th, 2011 at 10:23 am and is filed under Bees, Pollination, Squash. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.