Growing Winter Squash

March 1, 2024

By Will Bonsall

Buttercup squash
Will Bonsall prefers buttercup squash (C. maxima) for their sweet, dry flesh, which he says is comparable to sweet potatoes. Holli Cederholm photo

Winter squash are generally distinguished from summer squash by their drier, denser flesh, their sweetness and their storability, though it’s not quite that simple. Most winter squash belong to the species Cucurbita maxima, whereas summer squash (including zucchini) are all in the species Cucurbita pepo. Several winter squash are in fact also C. pepo, like acorn and delicata types. Butternut squash (tan skin, long fleshy necks) are also considered winter squash, although they belong to a third species, C. moschata.

Now I have always been a self-avowed pepo bigot, often disparaging C. pepo varieties as being watery and bland. Well, in my older years I seem to be developing a taste, albeit grudgingly, for at least some pepos, especially when eaten with stronger vegetables or condiments. Nevertheless, C. maxima continues as the undisputed top placeholder when served as a stand-alone vegetable, most particularly buttercup squash (not to be confused with butternut). In recent years, Tom Vigue and I have been trialing and stabilizing a cross he made between buttercup and Green Hokkaido. Its main advantage, in my eyes, seems to be lack of a “turban” shape, which causes waste when cleaning. Vigue had tentatively named the new cross Blue Moon, from its skin color and shape, but discovering an already-existing variety by that name has forced us to rethink it (the name will ultimately be his decision, as he is the breeder).

So, here’s what I’ve always preferred about buttercup (preferably Burgess Strain): Other winter squash may be delicious (read “dry and sweet”) when ripe and full-sized but are disappointing when even a bit immature. Buttercup, on the other hand, seems to begin storing sugar as it grows, not just after. That means that even a relatively poor-yielding crop will at least have good eating quality. By the way, even if I have some late-formed fruits with immature seed and rather watery texture, I still enjoy eating them boiled and mashed with some pepita meal to give a richer creamy texture. A way to avoid those runts is to pinch off any late-forming flowers before they waste any plant energy. That assumes you pay more attention to such details than I do.

I also prefer buttercup’s early maturity. I’ve direct-seeded them as late as summer solstice (June 21) and still harvested plenty of fully ripe squash. Anyway, gone are the days when I direct seeded my squash or any cucurbit for that matter. I resent feeding voles and other pest critters who love the oily seeds. Nowadays I only plant in 4-inch peat pots, three seeds per, and set them out as already well-established hills or clusters. This is especially helpful with varieties needing a longer, warmer season to fully mature, as all cucurbits are very frost-tender.

Squash breeding project
The fruit of a squash cross made by Tom Vigue, in which he selected away from buttercup’s classic “turban” shape. Sandra Lee photo

Squash are considered a “gross-feeder,” meaning they require lots of nutrients, especially nitrogen. Some crop species are actually harmed by excessive nitrogen, especially in proportion to other nutrients like potassium. Squash, on the other hand, are the real gluttons of the garden and seem to welcome all you can give them. They aren’t too picky about fresh manure or half-decayed compost, which other crops might resent. This is one crop I use well-composted humanure on (the other being corn) — I insist on the “well-composted” part, though the squash don’t demand it.

Although squash require ample fertility, I’ve come up with a strategy that allows that same squash plot to be self-enriched way out of proportion to anything added from offsite. This is how it works. In early spring, after the snow is gone but long before the soil is warm enough to plant squash, I sow the area to a very cold-hardy green manure crop, specifically oats, sometimes mixed with field peas. The oats sprout and grow slowly through the chilly weeks of spring, when the bare soil would otherwise be exposed to harmful elements. In late May, I chop in the young oats in 2-foot circles 4 feet apart, leaving the rest of the oats to keep growing. This is so the oats in the circles can begin to break down a bit before the squash crop goes in. Though green manures will release large amounts of nitrogen as they decay, in the beginning they will actually draw nitrogen from the soil to jumpstart the bacteria. Soon after Memorial Day I plant out the pots/hills of squash (3 plants in 4-inch peat pots), leaving most of the oats to continue growing.

By July 4, the squash plants are ready to sprawl, but the oats are by then about 2 feet high and preparing to head out to seed (which we don’t want as the ripe seed would become a weedy nuisance for the next year’s crop). At that point I take a 4-foot-by-4-foot half-sheet of plywood and flop it down on the oats between the squash hills, treading on it to flatten it out. Then I flip it and repeat until the whole area has been trodden down. Unfortunately, this won’t kill the oats but merely crimps the stem so that in a few sunny days the oats will try to straighten up again, creating a mess. To prevent that I spread a layer of last year’s old leaves over the flattened oats, excluding sunlight from the chlorophyl. Now the oats will give up and die and start to decay. I could use newspaper, cardboard or black plastic, but none of those grow on my land. To prevent the leaves blowing away I then spread a layer of old hay — weedy, seedy junk, it doesn’t matter — to act like a hairnet holding it down. It needn’t be a heavy layer, but hey, the more the better: It’s all organic matter for next year, right? Thus, we have three layers — the oat residue, the leaves and the hay — an impenetrable barrier to weeds and stabilizer of soil moisture, slowly releasing soluble nutrients every time the rain leaches down through that mulch. The squash vines will run rampant over that mulch, keeping the fruits clean and preventing rain-spattered soil-borne diseases from reaching the foliage. And here’s the kicker, which I cannot begin to explain: Squash grown by this method seem to be completely free of striped cucumber beetles, which may ravage nearby cucurbit crops grown conventionally. Moreover, other green manure crops (like clover) seem to confer some of this benefit, but nothing like the oats. Go figure. However, this system seems to have much less impact on squash bugs, for which I regrettably spray Pyganic. (Pyganic is a botanically derived pesticide approved for organic but still has very short-term toxicity and too broad-spectrum effectiveness for my liking.)

Winter squash mulched
Bonsall grows his squash plants with a mulch of crimped oats layered with leaves and hay. Sandra Lee photo

Although I generally harvest squash fruits after the first killing frost, I usually leave them in the field, piled and covered with a tarp on frosty nights. This is to allow sunlight and air to cure the skins for better storage. I’m careful not to handle them roughly, as cuts and bruises can greatly reduce storability. Even after picking the quality of the seeds will continue to improve, due to the seeds’ continued connexon with its placenta (the squash). This is important if you’re saving seed for future planting or if you intend to press high-quality cooking oil from them (see my previous article in The MOF&G, “Oilseed Pumpkins”). For longer-term storage, I place the fruits carefully on paper-covered wooden shelves — one layer, no touching — in a dry and cool but heated part of the house. Stored this way, I may enjoy them into the new year. And by the way, I’ve always considered a dry, sweet buttercup squash to be interchangeable with sweet potatoes, only easier to grow.

About the author: Will Bonsall lives in Industry, Maine, where he directs Scatterseed Project, a seed-saving enterprise. He is the author of “Will Bonsall’s Essential Guide to Radical Self-Reliant Gardening” (Chelsea Green, 2015). And indeed, he is also a distant cousin of another exemplary Maine horticulturist: Tom Vigue. You can contact Bonsall at [email protected].

This article was originally published in the spring 2024 issue of The Maine Organic Farmer & Gardener.

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