Squash - The Complete Guide to Growing Squash from Seed to Seed

Squash, Cucurbita spp.

Whenever you see ‘spp.’ tagged to a genus (in this case, the genus, Cucurbita), you should pay attention. It means species plural, i.e. there are multiple species of squash within the genus, Cucurbita. This is critical information for the seed saver, and some fundamental botany should explain why:

Varieties of the same species can cross pollinate; varieties of different species cannot cross pollinate.  

Cross pollination produces a hybrid seed. Hybrids can be fun for seed breeders, but not for predictability within our own food systems. Let me give you a solid example:

I grow the Tahitian Butternut (Cucurbita moschata) each year. It produces an extremely productive and massive fruit, is resistant to many fungal diseases and vine borers, and stores for up to 9 months. I rely upon this squash as a large part of my winter diet. If the Tromboncino variety (another Cucurbita moschata) cross pollinates, then all those traits I rely upon are threatened in the seeds that I save. The squash I grow the following year will not grow ‘true to type’. It may be an obvious cross like color or shape, but maybe I’ll just lose the excellent storability of the Tahitian. I may not even know the cross has happened until I have a basement of rotting squash in February, whereas I usually eat those squash all the way through May.

The Different Edible Squash Species

Predictability should be a key component to our food systems. So, knowing which of your plants can and will cross pollinate is critical, and knowing the species is the first step. Remember: A squash is not a squash is not a squash. A squash could be a Cucurbita pepo or a Cucurbita moschata or a Cucurbita maxima or a Cucurbita argyrosperma or Cucurbita ficifolia.      

Each of these distinct species have many variety options, but we can recognize broad traits between them. Here’s a quick breakdown to help you plan your garden:

• C. pepo: this species contains almost all of the summer squash, including zucchini, patty-pans, straightnecks and crooknecks. It also includes smaller pumpkins, hulless pumpkins (or naked seed pumpkins) and many small winter squash (including the Delicatas).
• C. moschata: this species includes all the butternuts and cheese pumpkins (e.g. Long Island Cheese). They are know for their long storage and solid stem vines, making them a good option where vine borers are a serious pest.  
• C. maxima: this species produces large winter squash which sweeten with age and have good keeping characteristics. It includes all the hubbards (and the Candy Roasters), a classic being the Blue Hubbard with tapered blossom and stem ends.
• C. argyrosperma: this species (previously C. mixta) originated in southern Mexico. It enjoys the heat and can tolerate humidity and includes all Cushaw varieties.
• C. ficifolia: this species is less common in North America but can be grown in temperate regions. In Central America it is commonly grown for its edible leaves (which resemble fig leaves, hence C. ficifolia) and seeds.

All squash are grown as warm season annuals in North America. The only real difference between summer and winter squash is when we harvest. Summer squash are bred to taste yummy when harvested immature; winter squash are bred to taste yummy when fully mature. All squash are heavy feeders and will need a good quality rich soil to thrive, adding composted manure will keep them very happy. Summer squash and some winter bush varieties will grow compact, but most squash will vine and romp all over your garden. The vines can root in at their nodes and a spade full of compost at those points will give healthier, better nourished plants.

Saving Squash Seeds

Squash plants have large beautiful flowers that attract many insects. This means cross pollination can happen up to a ½ mile. If you are just growing for fruit, this is not a problem. If you plan to save pure seed, the easiest option is to pick only one variety from each of the species. Since as only varieties of the same species can cross, you will have eliminated any chance of cross pollination (depending on your neighbor's garden…).

However, if you want to grow a Costata Romanesco Summer Squash (C. pepo) and a Small Sugar Pumpkin (C. pepo) and you don’t have a garden big enough to plant ½ mile apart, then welcome to the wonderful world of hand pollination.

In brief, hand pollination means you isolate the female flower from all insects (tape, rubber band, bag) the day before it opens. The next day you grab a couple of male flowers, expose the female flower and dab pollen from the male onto the female. Then isolate the female again. This guarantees that only pollen from the same variety is doing the pollinating and the seed from the fruit that grows from that female flower will be pure seed. Hand pollination justifies further research, but know that squash flowers are a great starting point for beginners. They are large and easy to work with.

Note: squash plants are described as Monecious, meaning they have separate male and female flowers on the same plant. Even if you don’t save seeds this year, be a botanical observer and learn the difference (you’ll notice squash plants produce way more male flowers than females, so go ahead and eat some of the males!). 

Ready to grow some squash? Check out our collection here!

	Article Written by: Angie Lavezzo
	About the Author: Angie Lavezzo is the former general manager of Sow True Seed. Beyond her professional role at Sow True, Angie's passion for gardening extends into personal hands-on experience, fostering plants and reaping bountiful harvests.