Both squash and zucchini, or courgette, belong to the Cucurbitacea family. Most are annual plants that are divided into several species:
Squashes are monoecious plants, meaning that they have both male and female flowers on the same plant. The female flowers have an ovary below the petals. It looks like a mini squash and will later develop. The male flowers are at the end of long stems. The flowers open for one day only.
The squash can be self-fertilised, meaning that the female flowers can be fertilised by pollen from a male flower on the same plant. However, cross-pollination is more common between different plants of the same variety and within the same species. Insects and above all bees pollinate squash flowers. The only inter-species cross fertilisation, also called inter-specifics, happens between cucurbita argyrosperma and Cucurbita moschata. It happens only rarely with a wild Cucurbita pepo. It is therefore generally possible to grow two species of squash next to each other without there being a risk of cross-pollination. It is, on the other hand, important to separate two varieties from the same species by a distance of 1km. This can be reduced to 500m if there is a natural barrier such as a hedge.
There are several methods to produce seeds from different varieties of squash grown in the same garden.
The first is to cover one variety with a mosquito net and to place a bumblebee hive inside. But this is difficult with the running varieties, as they rapidly fill up all of the space and prevent the insects from moving around easily.
Another method is to cover two varieties with two different net cages : open one while the other is closed on one day, and the other way round the next day. Let the wild insects do their work.
It is also possible to pollinate the flowers manually. It is relatively simple to do this, as the flowers are big and visible. These three methods are explained in greater detail in the modules on mechanical isolation techniques and on manual pollination in the ABC of seed production.
Squashes grown for seed are cultivated in the same way as those for consumption. Keep at least 6 plants to ensure good genetic diversity. Ideally, grow a dozen.
Take great care to select the plants you keep for seeds according to the specific characteristics of the variety, for example whether it is running or not. Check the shape and size of the fruit, the taste and texture of its flesh. Whether it has a good storing capacity. Also check its resistance to diseases.
A squash grown for seed is mature at the same time as squashes for consumption which are generally eaten when they are fully ripe. Exceptions are certain varieties of the Cucurbita pepo species, such as pattypan squashes and zucchinis which are eaten before they are mature. Let the zucchini, like the squash, ripen until its colour has changed, that it has attained its full size, that the peduncle is dry and hard, and in the case of zucchinis that its skin is hard.
You can then harvest them, place them in a warm place and let them ripen at least one month. With this technique the seeds’ fertility will be increased.
To extract the seeds, open the squash, and remove the seeds using a spoon. Avoid taking too much flesh. Rinse with water. With certain varieties it is difficult to separate the seeds from the flesh. In this case soak the seeds and flesh in water at room temperature and remove the seeds the following day.
Dry the seeds at a temperature between 22 and 25°C in a well ventilated area. To make sure the seed is dry, try to fold it. If it breaks it is dry enough.
Put a label with the name of the species and variety, as well as the year, inside the package, as writing on the outside may rub off. It is best to put the seeds in the freezer for a few days to kill unwanted parasites.
Squash and zucchini seeds have an average germination capacity of 6 years, but this can also last for 10 years. You can increase this by storing the seeds in a freezer.