Planting & Seed Saving Notes

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

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.

Tahitian Butternut

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.

Male and Female Squash Blossoms

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!


Written by Chris Smith, author of The Whole Okra, and Executive Director of The Utopian Seed Project, follow him on Instagram at @blueandyellowmakes.

2 thoughts on “Squash - The Complete Guide to Growing Squash from Seed to Seed

  1. avatar Sanoma says:

    This is for Gretchen Howard and anyone else experiencing something similar. Typically, summer squash such as zucchini, Crookneck Squash, etc, can have a delay on female flowers due to several factors such as: too much nitrogen (especially via fertilizers), weather temp, pest pressures, inconsistent watering/soil moisture. Normally, I’ve seen faster fruit production/female flowers if temperatures are in the mid-90’s during the day and nighttime temps don’t dip below mid-80’s. That may produce early fruit formation where the first couple of female flowers may not be pollinated because they’re appearing too early for you to be able to transfer pollen from the male flowers. If your plant takes a month, that’s perfectly fine, because it has more leaves and may suddenly produce a lot of female flowers. But if you’re still seeing only male flowers forming after then, you can side dress with some dry phosphorus and potassium. No more than a 1/4 cup should do it. Luckily…if the issue was too much nitrogen, that should decrease with watering, as well as, soil microbiology (unless frequently using high doses of synthetic fertilizers), allowing the plant to then refocus its energy from leafy-green growth to female flowers. Make certain to mulch the area near the plant to maintain soil moisture (which will also prevent back-splashing soil onto the stem and zuccs). Don’t overwater them though. Only thing to look for is not letting the soil dry out, as this will negatively effect fruiting. You can do foliar feeding intervals with kelp/seaweed, etc, to offer the plants more nutrients. Hope this helps.

    Happy harvesting!

    PS Nice introductory article. Was attracted to the picture. Had a surprise cucurbita maxima plant, not meant to be in the packet. Fruits look like between that Romanesco and a Dickinson. Guess I’ll be having something new/different that I didn’t hybridize, along with my butternuts.

  2. avatar Gretchen Howard says:

    Hello – I planted zucchini by seed on May 16. The plants and male flowers seem to be thriving with lots of pollinators, but I have not seen any female flowers yet. Any tips other than more patience? Is it possible that the plants won’t produce female flowers? I’d say it’s been 2-3 weeks since the male flowers arrived.
    Waiting on the ladies-

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