Squash Pollination! Hurrah!

Now that everyone has planted their fall carrots and other roots (right?)..... you might want to plant more Swiss chard in the next week or two to make sure you have enough for winter harvests. I sow leaf beet in July, which is a hardier, finer stemmed version of chard, to supplement the bed of chard planted in May. Early July is also a good time to plant kohlrabi, radicchio and various other endives for late summer through winter harvest.

Squash pollination can be a issue this time of year, especially when the activity of bees that pollinate the flowers is curtailed by cool weather.

A common problem is that newly developing squash seems to grow a little bit, but then growth stops and the small fruit falls off or rots. This happens because the flowers were not fertilized.

To make sure you have a crop, you may have to pollinate flowers by hand, at least in the early part of the season. This is particularly important right now for winter squash because the flowers have to be fertilized in the next couple of weeks so that the developing fruit has enough time to mature fully. This contrasts with summer squash, which can continue to set new fruit into early fall because they are picked while immature. 

Squash pollination can get a bit complicated so hold onto your hat:

First, you need to know that squash (and pumpkins, melons, etc.) have both female and male flowers. Female flowers have a miniature squash on the stem right below the flower. Male flowers just have a straight stem. They also clearly have pollen, which looks like yellow dust, on the centre structure. To pollinate, pick a male flower, peel back the petals and dab some of the pollen from the centre of the male flower onto the centre structure of any female flowers that are open. Flowers open in the morning so that's the best time to do the pollinating.

Early in the season, there may only be one sex of flowers present on a plant. Open pollinated varieties usually produce male flowers for several weeks before they start to produce female flowers. This gives the plant time to grow big enough to support a good crop. Some hybrid squash produce only female flowers at first. I have learned to resist the temptation to pollinate those first blossoms if the plant is small as it stunts future production. If you grow two or three plants of a few different varieties of squash you have pretty good odds of having both sexes of flowers present at the same time.

A complicating factor is that there are different species of squash. The pollen from one species cannot fertilize flowers from a different species. Three groups of species are commonly grown in this region:

Cucurbita pepo group includes all acorns, crooknecks, scallops or patty pans, zucchinis, vegetable marrows, spaghetti squash, many pumpkins and Delicata;

Cucurbita maxima group includes banana squash, buttercups, hubbards, turbans

Cucurbita moschata group includes butternuts and tromboncino

As long as you stay within the group when moving pollen around, the flowers will be successfully fertilized. If you don’t know what species you have, just stick to transferring pollen from male flowers to female flowers within the same plant.

Seed catalogues are getting much better at showing the species in the variety descriptions so it isn't hard to find this information. I make a note of what I can cross with what in my squash patch in case there is a shortage of male flowers. For example, this year I have butternuts, which can only be pollinated by butternuts and I also have 3 varieties of pepo group squash so they can all be cross pollinated as needed.

 Don't worry about what the fruit will be like from crosses--the mixed genes only show up in the next generation, which you would see only if you grew out the seeds from the fruit.

One way out of the pollination problem for zucchini lovers is to grow a parthenocarpic cultivar. These set fruit without needing to be fertilized. This year I am growing one called 'Partenon' from William Dam Seeds (http://www.damseeds.ca/productcart/pc/home.asp) and sure enough, had very early fruit from a plant when there was only female flowers present. If you only have room for one squash plant, this is your best bet!

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