Squashes are wonderful. They are incredibly varied, delicious, and nutritious. Some are sweet, some savory; some have hulless seeds; some will store for many months. They also have large, generous flowers which bees love, and they depend on insects to pollinate them. So if you want to save seed from squash and have it remain true-to-type, there are some important things to understand.
Background
There are three species of squash which are commonly grown in Ontario: Cucurbita pepo, which includes summer squash, zucchini, acorn squash, hulless-seeded squash, and most pumpkins; C. maxima, which are Hubbards and various larger squash; and C. moschata, which includes the butternuts, cheeses, and many other things. Most of us ordinary mortals cannot look at the fruit of a squash and tell which species it is, though there are differences in the flowers, leaves, stems and seeds which can give you hints about its species. As long as you do not have near neighbours growing squash, you can grow one variety of each species and they will stay pure, because they don’t cross with each other.*
However, if you want to save seed from more than one variety of a species, you will need to take some precautions. The standard solution to prevent the bees from cross-pollinating your squash is to become a bee yourself, in a process called hand-pollination. Hand-pollinating squash is quite easy and takes only a few materials; I quite enjoy it. You can find directions for how to do it from many different sources, but my technique uses slightly different materials from most, so I will explain it.
The botanical basics vital to pollinating squash are that each plant has separate male and female flowers which only live for one day. The flowers open early in the morning. During the day, bees visit each flower many times to collect the nectar they gradually produce. In the process, the bees receive a dusting of pollen in the male flowers, and accidentally brush off some of that pollen on the stigma of a female flower when collecting nectar there. At the end of the day the flowers die. Males usually drop off the plant, as do females that have been inadequately pollinated (females may also drop if the plant decides that it cannot support more fruits to maturity). To hand-pollinate, all you need to do is to keep the bees shut out of the flowers, and move pollen from the males to the females yourself. For this you will need pollination bags and a bunch of strings about 6-8” long. I use small cloth bags made out of old sheets, and old baler twine.
Technique
Day 1
Start in the evening, to find blossoms which will open the next morning. Check carefully under the leaves; squash blossoms like to hide and then leave you chagrined when you find them wide open the next day. Blossoms at the right stage will be swelling and usually turning yellow or orange, but are still tightly shut. Look through your squash patch for female flowers first. Females and males are easy to tell apart: females have an ovary just below the closed petals which usually looks like a tiny version of the squash. Males don’t. When you find a female, put a bag over it and tie a string around the bag to hold it shut, just below the ovary. I use a single overhand knot. Once you have bagged all the females, you need to find males. Ideally, I like to use two males flowers per female flower, preferably using males on a different plant from the female. If you don’t have enough males for this, it is possible to pollinate with a single male; I use two just to ensure I have lots of pollen. The occasional male won’t work for some reason, so for every three females, I like to find one extra male for insurance (for a ratio of 3:7). Use a string to tie the males shut with a single overhand knot around the petals, a little below the tips. Do not pull too tight; if you do, you can cut right through the petals. If a flower has holes chewed in the petals, or if it opens at all overnight, don’t use it, since bees could have contaminated it with pollen from another plant.
Get a good night’s sleep (recommended, but not essential).
Day 2
Around dawn the next morning, go out to your squash patch. Locate a bagged female. Find two male flowers on another plant which are still tied shut. Pick the males, with a bit of stem still attached, and carry them over to the female.
The next steps should be done swiftly, to decrease the risk of a bee diving into the flower and contaminating it. It helps me to think of them as a dance between male and female.
1. Untie the twine on the female’s bag, leaving the bag on for now.
2. Take a male and pinch the petals at the base. Carefully tear away a section, avoiding touching the anther and knocking off pollen. This makes an opening so that you can easily grab the rest of the petals and tear them away, leaving a pollen-loaded “paintbrush.”
3. Unbag the female. Paint the pollen from the male on the three sections of the female’s stigma. The pollen should be visible as an orange powder.
4. Tear the petals off the other male. I like to hold the male flower over the female for this, so that I can keep an eye on the female to watch for bees even while preparing the male flower. Pollinate the female with the second male.
5. Tear the tips off of the female petals, leaving them just a bit longer than the stigma. This serves two functions: if you get confused about whether you’ve hand-pollinated this flower or not, you can check the petals and see; and it makes it easier to fit the bag back over the flower. Rebag the female and retie the twine below the ovary.
I leave all the petals and the used male flowers in a pile next to the female, to make it obvious that I’ve hand-pollinated that flower already.
Follow-through
Now each morning and evening as you go through your patch finding new flowers, check each already-pollinated female. I like to leave them bagged for about 36-48 hours after pollination, to make sure that the fruit has taken and the flower is dead (and thus can’t be pollinated further after the bag is removed); but it is very important that you remember to remove the bag. Otherwise the squash will grow to fill it like a sausage, and either be killed or deformed by it or burst it.
When you remove the bag, retie the twine around the stem with a square knot as a marker so that when you harvest in the fall you will know which fruits have been hand-pollinated. Make the twine as loose as you can, while still making a loop smaller than the squash; the fruit’s stem will grow and be cut by the twine if it is too tight.
In the fall, harvest, cure and store the squash as you would for eating. Collect the seeds when you open them. Wash them clean and spread them on a screen or plate to dry. Make sure that you save seed from at least six plants, preferably more, to avoid inbreeding depression.
A few weather-related details to note:
– Squash flowering is very connected to temperature and moisture. In the day or two after a rain, expect a lot more flowers. This also affects how long it takes to pollinate a few fruits on each plant in your patch. In my unirrigated conditions, I expect to be out pollinating a variety daily for about two weeks.
– Flowers due to open the next day can open late in the evening if there has been a good amount of rain during the day. If it has been raining, you may want to find your blossoms late in the afternoon rather than waiting for evening.
– If it is very cold overnight, the males may not be shedding pollen at the usual time in the morning. This is obvious; the anthers look paler and thinner, and you won’t see any orange powder. If this is the case, just wait an hour and try again.
*Various people have reported inter-species cross-pollination in squash, but as far as I can tell, these are rare and tend to result in sterile hybrids, so they are unlikely to threaten your varietal purity. I have never personally seen one. [Back to main text]