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A Pollination Moment
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Summer Squash Diary Blog 
Read about our 2006 Summer Squash Research Project:
Harvest Frequency, Yield, and Economics of Summer Squash

9/21/2002
Squash Blossoms

Summer squash are probably the most prolific plant in the garden, as long as squash bugs and borers don't kill them.  One should pick summer squash daily to avoid growing baseball bats and flying saucers.  The summer squashes - Zucchini, crocked-neck squash, patty pans, and the like - all grow from large golden, trumpet-shaped flowers that open in the morning and are generally pollinated and closed by the end of the day.  Some of the flowers are female, containing the pistil that will grow into the squash fruit.  These flowers have lots of nectar to attract bees.  Other flowers are male, containing a column of fused anthers covered with large gold pollen grains.  They also contain nectar, so bees visit for both nectar and pollen.

Bees are absolutely necessary for squash pollination, because they are the only way that pollen can be moved from the male flowers to the female flowers - unless you get out there in the morning with a small paintbrush and move the pollen around yourself.  If you grow squash and they are deformed - very narrow at one end for example, you may not have enough pollinators; but here in Idaho that is probably rare.  Honey bees do a good job of pollinating.  I've also seen sweat bees in my squash flowers - the gorgeous bright green metallic Agapostemon is common around here.  But if you plant squash each year, more than one or two plants, you probably have squash bees pollinating in the morning.  These are digger bees, approximately the size of honey bees, but they move faster, and are more brownish-gray and white in color than the orange and brown honey bees.  Males patrol the squash bed, visiting flowers to find females to mate with, and to drink nectar so they have the energy to do all that flying.  Females visit the male flowers for pollen for their offspring, as well as drinking nectar.  They are more directed in their flight, and not so skittish as the males.  There are two genera of squash bees, Peponapis and Xenoglossa, and several species.  They forage only from squash blossoms.  They nest in the ground, and some of their nests go deep - as much as a foot or two.  They are more likely to be present if you don't use pesticides, and if there is uncultivated land nearby for them to dig their nests without disturbance.  Aside from leaving some land undisturbed around the garden or squash field, we don't know how to manage these bees, but hopefully some day we will.  It is thought that the distribution of squash bees all across the US has expanded as squash plants were cultivated and distributed around the country by Native Americans and early European settlers in the New World.
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September 21, 2002
Copyright © 2002, Karen Strickler. All rights reserved.