When harvesting seeds at home, safeguarding their purity can be a bit of a delicate operation. But with pumpkins, squash and other members of the ‘Cucurbitaceae’ family, it can be downright tricky.

First of all, let’s clarify a common misconception that all members of the ‘Cucurbitaceae’ family can cross-pollinate each other. The fact is that a pumpkin will not cross-pollinate with a melon, a cucumber will not cross-pollinate with a zucchini, a lauki will not cross-pollinate with a tinda and so on.

Just imagine the weird and wonderful range of fruits that would appear in the market if cross-pollinating at random were really the case. A melon crossed with a cucumber? It just doesn’t happen.

However, if grown in close proximity, a white cucumber will cross with a green one. Plants grown from the resultant seed are liable to have characteristics of both parents — so basically a green cucumber with white streaks, or the other way round.

Saving seed from garden vegetables is rewarding but challenging, especially with species that cross-pollinate and are growing in proximity

Now back to pumpkins. A huge range of pumpkins are grown all around the world. Some of them are considered varieties while the names may often vary from country to country or from region to region within a country. Other varieties may have no name at all, having been cross-pollinated so many times over so many generations that their origins are lost in the mists of time.

The pumpkin species itself, is further broken down into four predominant ones: ‘Cucurbita maxima’, ‘Cucurbita mixta’, ‘Cucurbita pepo’ and ‘Cucurbita moschata’. Each of these species have numerous sub-species of their own, and these sub-species will cross with other members of their own specific group if grown close together. They will not cross with sub-species from the other ‘cucurbita’ groups mentioned.

The ‘Cucurbita maxima’ species, which includes the well-known sub-species such as Atlantic giant, Turk’s turban, Hubbard squash, pink banana and Rouge vif d’Entampes, will all merrily cross-pollinate and, unless you take strict control, in very few years, your saved seeds will produce pumpkins resembling none of the above.

Allowing free cross-pollination may or may not bear good results and must be avoided, especially if you are trying to save heritage species.

There are a couple of sure-fire ways of maintaining pumpkin — and other ‘Cucurbitaceae’ — purity.

1. Grow only one species of pumpkin from each of the aforementioned four groups. These will not cross with each other but, if someone close by or within a radius of about 400 meters happens to be growing a different species from the same group, your pumpkins may cross pollinate with those through insect and/or wind pollination.

2. Pollinate selected plants, preferably the strongest and healthiest, by hand. Keep a close eye on the development of both the male and female flowers of the exact same pumpkin species. These can be on the same plant. On the evening before you anticipate the flowers will open, use a strip of clear adhesive tape to carefully fasten the top of the flowers and close them. This stops them from opening at dawn the next day, preventing any insect/wind pollination from occurring before you do the job yourself.

Early next morning, snip off the closed male flower then delicately remove all of its petals to expose the male parts within. Next, carefully open the female flower, leaving petals in place and gently rub the center parts of the male flower against those of the female, transferring the male pollen on to the female in the process. On completion, close the female flower up again. If the petals are too damaged to do this, encase it in a fine piece of muslin instead, to prevent any unwanted pollination. Leave the flower in place until fruit is set and it naturally withers and drops off.

Leave the resultant pumpkin/s on the plant until they are fully ripened and, after harvesting, wait at least another month before opening the fruit/s and removing the seeds.

Clean off any adhering flesh from the seeds, air dry them and store in an airtight container in a cool, dark place. They should remain viable for at least 3-10 years. This applies to all members of this widely diverse and endlessly fascinating family.

*For the uninitiated: A male ‘cucurbita’ flower is borne on a long stem whilst a female flower which has a small swelling at its base which will become the fruit, is on a very short stem. Both male and female flowers are on the same plant.

Please continue sending your gardening queries to zahrahnasir@hotmail.com. Remember to include your location. The writer does not respond directly by email. Emails with attachments will not be opened

Published in Dawn, EOS, July 18th, 2021