Squash for Winter

Cucurbita maximus, & C. moschata

Cucurbita is the genus, and within it are various species that grow the squash fruits we eat.

Introduction

Cucurbita is the genus, and within it are various species that grow the squash fruits we eat. There is an excellent summary of cucurbits in Wikipedia. The two species of this lesson are maximus and moschata, for winter squash. The species C. pepo includes all summer squash.

C. maximus plants can be bushy or trailing. Maximus includes many common varieties: Buttercup, Hubbard, Kabocha, Kuri and Turban.
C. moschata are trailing plants that need more warmth than maximus to bring fruits to maturity, and the most commonly grown variety is Butternut.

The description ‘winter squash’ is for fruits that mature with a hard skin and dense, dry flesh. As a result, they store or keep for many months, making them an excellent reserve of winter food, whatever the weather.

4th July 2020 – a squash bed interplanted with a few sweetcorn, seven weeks since transplanting

10th October 2013 – my first harvest of squash at Homeacres from new land, no dig and full of weeds in March; from left to right: Uchiki Kuri, Crown Prince and Buttercup

Crown Prince in halves; this is February, four months after harvesting, and the amazing coloured flesh offers deep and sweet tastes

Harvest period

Days from seed to first harvest: 120 for early varieties such as Red Kuri, from seed to last harvest: 180

Best climate is a warm or hot summer, with afternoon temperatures close to or above 22 °C/72 °F for at least two months, and average rainfall, say 50–100 mm/2–4 in per month.

So what is a pumpkin?

There is confusion between squash and pumpkin. ‘Pumpkin’ is used often to describe all Cucurbita plants; however, as Wikipedia says, ‘The term pumpkin has no agreed botanical or scientific meaning.’

I find it vague, because it is used to describe both what I would call true pumpkin, as well as the winter squash I describe here.

True pumpkin fruits are usually larger than squash, with softer skin and flesh that is less sweet.
They have a high water content, hence the heavy weight, and hence also the poor storage capability, often decomposing within two months of harvest.
There is not a clear boundary between what are called squash and what are called pumpkin. Sometimes we have been disappointed by squash when eating them, by a lack of flavour, and sometimes they also rot in storage more quickly than I expected, from the description given.

Ian Stott at Hauser and Wirth Somerset’s Pumpkin Festival in 2019, with his winner – a 167 kg/367 lb Atlantic Giant pumpkin

Weighing a pumpkin at the festival on 27th October 2019 – a two-person job

Why grow them

Just check these three conditions:

Your climate is warm enough.
You use appropriate timings for sowing and harvest.
Your soil is fertile which, with no dig, means a minimum of 3 cm/1 in of surface mulch of old organic matter.

If all three conditions are met, you will have a bountiful harvest of excellent flavour which stores for several months.

There are few pests, although in North America the squash borer is a problem. I have never suffered it and read that a mesh cover from planting to early fruit stage can protect plants. In the UK at least there are few pests and these vegetables are easy to grow, mainly in the country’s warmer southern half.

30th May – squash plants, ten days after transplanting; yellowing grass shows how dry the weather has been through spring

28th July – the Crown Prince are trailing over dry grass; soon after this we had some rainstorms, which continued through August

Five weeks later, in early September, after dieback of the leaves; two squash have matured on the grass area and there were many roots into the grass-covered soil from the trailing stems

Pattern/phases of growth

Growth is exceptionally rapid in high summer, when leaves quickly grow large and high, and then soon die back again within a few weeks. In areas of temperate climate, with summers just warm enough to grow mature winter squash, it helps to understand squash growth in these phases. Phase 1 is not needed for climates with long, hot summers.

Sow undercover with extra warmth, to have transplants ready by the date of your last frost.
Growth is rapid in the warmth of high summer and when soil is fertile, with sufficient moisture.
Like all cucurbits, squash plants root very rapidly into surface mulches of well-decomposed organic matter, on top of undisturbed soil.
By late summer, new growth slows down, older leaves have mildew and fruits develop rapidly.
With the onset of autumn, most leaves die and fruit develop a hard skin, at which point they can be cut to store.
For a week after harvest, keep fruits as warm as possible so that they ‘cure’, with skins becoming fully dry and hard.

12th July – there are six plants of Kuri squash here and they’re starting to invade the cabin!

As early as 7th September, the Kuri squash already have 15 ripe fruit with dark red, firm skin, but they are on the small side from being a little short of water

After a wet summer in 2012, the fruit are much larger; here’s the Kuri squash harvest on 5th October

Suitable for containers/shade?

Neither of these is easy, although growing in shade is possible if you are in a very hot climate. Plants need an extensive root run and space to grow many leaves. Use a container the size of a very large bucket or bigger, water regularly and give some feed too.

Kuri squash are worth a try, being smaller plants. They either need space to run outside the container or a support structure if the weather is not too windy.
If you give them the means to grow, they are adaptive, as you see in the photos below!

October 2012 – I grew a Kuri plant in a compost heap, which was enclosed by pallets

After sawing two planks of wood off the pallet, I could harvest the squashed squash!

Varieties

Maximus

Kuri varieties, sometimes called ‘onion squash’ because of the fruit’s shape, are fast to mature. They come with many names, including Red Kuri, Blue Kuri, Uchiki Kuri, Solor and Orange Hokkaido. The latter are a little larger, while most Kuri weigh 1–1.5 kg/2.2–3.3 lb.
Crown Prince are a reference point for sweetness, depth of flavour and longevity of storage. As well as being sweet, we really miss the ‘something extra’ in their flavour, when cooking with other, similar varieties. It’s available mostly as F1.
Marina di Chioggia tops many taste tests and is large – quite easily grows up to 6kg/13lb – but grows maybe just two fruits per plant. They are ribbed and not easy to peel, and the dark green skin at harvest turns golden brown when ripening in long-term storage.
Kabocha, from Japan, have dark green skin, orange flesh and are of medium weight on vigorous plants.
Buttercup is one of many ‘Turban‘ varieties, with dark green flesh and weighing 1.5–2 kg/3.3–4.4 lb. Plants stay reasonably compact.

Mid-October – the Crown Prince harvest from four plants, with an average weight of 3.7 kg/8.1 lb; this is a lot of food to see us through winter and spring

Musquee de Provence squash has excellent flavour and also stores very well

These Buttercup squash are ready to harvest on 10th October, shown by their stalks being mostly dry

Moschata

Butternut are prominent in the UK as the default squash served in restaurants and pubs, thanks to their excellent flavour and keeping quality. A word of warning is that they need more warmth to grow and mature than other varieties here. I have had many frustrating autumns waiting for my butternuts to ripen before it was too cool, and often they did not so we ended up eating marrows!

Musquee de Provence is similar in appearance to Chioggia, a little smoother skinned but with a less sweet flavour. The flesh is a little less dense and fruits are even larger.

Musquee de Maroc is better looking than tasting – it has amazing warts and can be multicoloured in a hot summer, from green and yellow to orange and brown. The flesh is more watery than Musquee de Provence, so the fruits do not store for more than three months.

Summer squash, Twinkle F1 – they are highly productive, but a lot of the harvest is water, compared to winter squash

This selection of winter squash includes F1 hybrid Butternuts, which did not yield a lot but ripened earlier than open-pollinated Butternut

Cooking

Winter squash offer an extra dimension of flavour, compared to pumpkins. It’s a combination of sweetness and also savoury, with a density of texture that makes them hard to enjoy on their own. Like potatoes, they need some fat, salt and soft accompaniments such as onions and leeks.

Stephanie Hafferty makes an amazing squash soup – see her book, The Creative Kitchen. A key part of the process is to dice the squash and roast it, before turning it into soup. The roasting brings out an incredible sweetness and extra flavour.

Kate Forrester, another chef who gardens at Homeacres, cuts Crown Prince into pieces or thin slices and does not remove the skin. When roasted, the skin is edible and tasty.

Video

Growing winter squash, including on compost heaps

Sow and propagate

In warm climates, you can sow outside very easily, just as long as the soil temperature is 20 °C/68 °F or higher.

This section is more about sowing under cover, in regions where summer is not quite long enough to include the propagation phase as part of outdoor growing.

A seed germination comparison, with both seed packets bought at the same time, one year earlier – Seed Coop Solor on the left and King’s Crown Prince on the right; other Seed Coop seeds have grown fine – this is just to highlight the occasional element of uncertainty

Seeds germinate in four to seven days, depending on warmth.

Sowing time

Sow approximately one month before your last frost date. This allows sufficient time to raise a large plant, which effectively gains you a month of growing time. At Homeacres we sow around the middle of April, and definitely before the end of April, to transplant in mid-May.

Mid-April, sowing winter squash seed under cover with one per module; laying it flat is absolutely fine

25th April – the plant and seedling selection on the hotbed, with squash emerging and aubergines front right

Sowing method

Smaller modules are better than large pots for two reasons:

They need less space if you want to keep them warm during the germination phase.
There is less chance of overwatering and seeds rotting. A 5 cm/2 in cell diameter works well, and a similar depth, no more.

There are many suggestions about which way to place seeds when sowing – up, down or across. We find that simply flat on their side works really well. Roots come out of the slightly flatter end and easily find their way down into the compost.

Use any multipurpose, potting or container compost – there is no need for sowing or seed compost.

Water trays to capacity either just before or after sowing, then water little for the first week.
It is worth germinating them in your house if your climate has cold nights at sowing time.

These 5 cm/2 in wide module cells are an excellent size for sowing squash seeds, which I’ve laid on top and pushed in a little

Mid-April, sowing quash seed; the same trays after covering with potting compost

The same sowing again, after sixteen days on the hotbed; we then we pot them on, and, if it were the right season, we could transplant at this size

Pot on?

This is a necessary phase of raising these fast-growing plants, when there are more than two weeks between sowing and transplanting. Once seedlings are at the stage in modules where leaves touch each other and stems are elongating, you will also notice that the roots have filled all available module compost.

Pop rootballs up from the cells with a gentle push, and place them at the bottom of a 10 cm/4 in pot. Fill that pot with more of the same potting compost and keep reasonably warm, as before, always with frost protection if nights are very cold. Should frost be forecast, this can be a layer or two of fleece or row cover over the top of all leaves in the evening, until soon after dawn. You don’t need to cover the plants every night.

28th April – it’s time to pot on these squash after two weeks in modules

A close-up of potting on cucumber; it’s the same process with squash – dropping the module rootball into a pot so it is surrounded with extra compost, and burying the stem to make it shorter plus stronger

A morning watering of plants in mid-May; many are now ready to go outside and the last frost date has passed, the soil is warming fast

29th April after potting on squash plants, seen on the table to the right of the hotbed

5th May after a frosty night; in the evening I had laid fleece over plants in the greenhouse, most of which are tender to cold – it was 1 °C/34 °F in the greenhouse

Transplant, interplant

Transplant size and time

These plants are very tender to frost, so you must be absolutely sure that no more frost is possible after you have transplanted them. Plants can be quite large, preferably not yet flowering, and the pots may be brimful of bright white roots.

Should a very cold night be forecast when plants are in the ground, lay fleece over them on the evening before, to be on the safe side. One late frost is enough to lose a whole harvest.

1st June 2018 – companion or interplanting of squash and beans, with perennials; Buckler leaf sorrel bottom left

28th July – beans growing between the squash plants

7th September – leaves of these Borlotti teepee plants are turning yellow as their bean pods start to dry

Transplant method

Make a hole slightly larger and 5 cm/2 in deeper than the pot size, then push the rootball in firmly. You want to bury the stems, or some of them, for two reasons:

So that plants do not blow too much in the wind.
To make it easier to maintain a high moisture level around the new rootball, for at least its first two weeks in the ground.

I find that that the 10–20 days after transplanting are critical, for both of these factors.

In 2017, we lost six squash plants to a high wind, 50 mph gusts, on 6th June, three weeks after planting. Somehow it rotated plants around until the stems snapped off.
Then, in 2018, it was the opposite, with fine weather and extremely hot sun. This meant that although we laid fleece over new transplants, within three days we needed to remove it because they wilted so fast in the afternoon, even though fully watered in the morning.

The long and the short of it is that these plants grow, and need to grow, extremely fast. Until the roots are well established, keep an eye on them water-wise during dry weather.

These winter squash have been planted through holes in the polythene in late May

If perennial weeds are strong… as well as having polythene over them, we slotted a piece of cardboard into the planting hole to reduce light available, to bindweed in particular

Five weeks later – the squash plants have their roots down and are exploding into their fastest month of growth through July

Interplant

Despite their leaf size and vigour, squash plants lend themselves to interplanting as they actually don’t need a long time to grow. The season of full growth for winter squash is shorter than that of summer squash, which continue to grow right into autumn and until first frost. Plus the wide spacing allows other plants to establish and get underway in the empty areas between, before squash have used every bit of the ground.

The native Americans had a way to use this space with an interplant called ‘Three Sisters’. Between each squash plant were some corn plants and next to each corn was a climbing bean plant. The desired harvest was dry corn, or maze, and dry beans. However, if you try to pick sweetcorn from a Three Sisters planting, it can be difficult and damaging because the bean stems are twined around the corncobs.

This does not matter in mid-autumn, when a dry harvest is taken of everything.

Unless your summer is hot enough to allow easy maturity of dry beans, Two Sisters with a sweetcorn option is more viable than Three Sisters.
In temperate climates, an option would be to transplant two sweetcorn in the gaps between each squash plant.
Or make a small teepee for beans to harvest dry, again in the space between squash transplants.

Both of these interplantings may require extra watering. They are an efficient use of space.

Spacing

1 m/39 in is a good all-round figure. Kuri varieties can be closer, at 75 cm/30 inches, while Butternuts and Crown Prince can use a little more space.

When days are warm and there is enough moisture, any extra space between plants is not wasted, because of how they put roots down from the trailing stems. They feed into path soil as well.

This is one part of growing enormous pumpkins – allowing loads of space for one plant and thinning fruits to one per plant.
With winter squash plants you do not need to thin at all, they sort that for you!

19th May – see how few plants are here, with 1 m/3 ft spacing between them; this is a mulch trial, with seaweed at the far end, and there will be miscanthus at the near end

High summer – all the squash plants are keen to invade and we’ve been cutting them back to keep the lettuce bed producing! There’s no clear difference visible between plants growing in the different mulches

21st August – a nice harvest of two sisters sweetcorn Earlibird, with squash of mixed varieties

Support

In theory, one can grow these plants up trellises and many kinds of support. I find in practice that they are not too happy growing in that way, and certainly not where it may be windy.

In sheltered gardens, and where you have time to tie stems to a structure, it’s a fun thing to try.

13th June – squash planted eighteen days earlier have benefitted from a fleece cover in the cool summer of 2012

A question of support – these Kuri plants were keener to grow at ground level, rather than up the trellis

Transplant size and time

Should a very cold night be forecast when plants are in the ground, lay fleece over them on the evening before, to be on the safe side. One late frost is enough to lose a whole harvest.

Transplant method

Make a hole slightly larger and 5 cm/2 in deeper than the pot size, then push the rootball in firmly. You want to bury the stems, or some of them, for two reasons:

So that plants do not blow too much in the wind.
To make it easier to maintain a high moisture level around the new rootball, for at least its first two weeks in the ground.

I find that that the 10–20 days after transplanting are critical, for both of these factors.

In 2017, we lost six squash plants to a high wind, 50 mph gusts, on 6th June, three weeks after planting. Somehow it rotated plants around until the stems snapped off.
Then, in 2018, it was the opposite, with fine weather and extremely hot sun. This meant that although we laid fleece over new transplants, within three days we needed to remove it because they wilted so fast in the afternoon, even though fully watered in the morning.

The long and the short of it is that these plants grow, and need to grow, extremely fast. Until the roots are well established, keep an eye on them water-wise during dry weather.

Interplant

This does not matter in mid-autumn, when a dry harvest is taken of everything.

Unless your summer is hot enough to allow easy maturity of dry beans, Two Sisters with a sweetcorn option is more viable than Three Sisters.
In temperate climates, an option would be to transplant two sweetcorn in the gaps between each squash plant.
Or make a small teepee for beans to harvest dry, again in the space between squash transplants.

Both of these interplantings may require extra watering. They are an efficient use of space.

Spacing

1 m/39 in is a good all-round figure. Kuri varieties can be closer, at 75 cm/30 inches, while Butternuts and Crown Prince can use a little more space.

When days are warm and there is enough moisture, any extra space between plants is not wasted, because of how they put roots down from the trailing stems. They feed into path soil as well.

This is one part of growing enormous pumpkins – allowing loads of space for one plant and thinning fruits to one per plant.
With winter squash plants you do not need to thin at all, they sort that for you!

Support

In theory, one can grow these plants up trellises and many kinds of support. I find in practice that they are not too happy growing in that way, and certainly not where it may be windy.

In sheltered gardens, and where you have time to tie stems to a structure, it’s a fun thing to try.

Water

Once your plants are watered in and starting to grow strongly, it may be that you don’t need to water for quite a long time. Winter squash mostly start their life with the benefit of soil moisture from a previous winter.

More than half of their lifetime’s needs should already be present in the soil.
In the second half of summer, they need water for developing several fruits.

Or, if it’s dry and you do not water, plants survive but will fruit less. For more harvest, water once you see many small fruits, if the soil is dry – give a decent soak, twice a week.

October – just three plants of Crown Prince achieved all this, thanks to feeding in nearby beds and under fruit bushes

Extra mulch to retain moisture and kill weeds?

Plastic mulches, for smothering summer weeds, combine well with growing widely spaced squash plants. You need a few holes in the plastic and it can then be easily used again for a similar purpose, to kill weeds through light exclusion.

You can plant through plastic by first cutting a cross with a sharp knife, giving four diagonal flaps. It’s not too difficult to then make a hole through these with a trowel and pop in the rootball of your squash plant.

How does this plant receive water, when its roots are below impermeable plastic?

The answer is that rainfall drifts around on top and a lot of it goes in the plant holes.
Plus the plastic cover also retains moisture in the first half of summer.

It’s a neat option if you have bindweed, for example, because for both squash and bindweed, the season of growth is summer. The plastic mulch deprives new bindweed of shoots of light, while squash leaves use the light above and roots take the moisture from below.

4th June, after we had planted squash through the green polythene, which is covering grass and has 5 in/12 cm of compost underneath; the polythene to the left is covering weeds and has potato plants growing through slits

Eight weeks later, showing the large leaves of squash in high summer

30th September, just after the squash harvest; the only remaining weed is field bindweed, Calystegia

Thin fruits/leaf removal

This header is not needed, but it’s here to make the point. You don’t need to thin fruit, nor do you need to remove old leaves! Yet I am so often asked, ‘do I need to thin fruit’? You don’t.

Another question is common as summer concludes, when many leaves develop mildew. Does this matter? The answer is no, because it’s a normal part of the life process.

Leaves work hard for only six weeks or so, then they die as plants no longer need them.
Mildew is the process for this change. As leaves die, you suddenly notice lots of winter squash fruit.

Video

Growing winter squash, including on compost heaps

Harvest times and methods

How to judge readiness

For winter squash to store (in comparison to summer squash mentioned below), they need to be fully developed, with a hard skin and sweet flesh. If they are picked before this stage you still have food to eat, but it is less sweet and does not store for so long. It is more like a ripe summer squash, with firm skin, seedy flesh and decent flavour.

A sign of ripe squash is the stalk going dry. In fact, when the fruit are ripe, you can’t actually cut the stalk anymore because it is so wiry and tough. That is a good sign!

‘Two Sisters’, sweetcorn and squash, on 31st July – Kuri show ripe, red colour for up to a month before harvest

Summer squash under a five-year-old apple tree – this combination needs a wet summer; the plants and trees are needing plenty of moisture

30th September – Uchiki Kuri squash are ready for harvest, with tough stalks and the leaves having almost all died off

How to pick

Best wait until all fruits are ready to harvest. Do not pick the few immature ones; they can go to your compost heap because, by autumn, they will not grow or ripen anymore.

Handle fruits carefully and do not damage their skin, for long storage.

Cut the plant stems either side of each stalk, rather than trying to cut the stalk itself.

This avoids damage to the fruits. Sometimes, when trying to cut a squash stalk, it snaps off, making an open wound in the fruit itself. This squash will then not store for more than about six weeks.

When to pick

Watch the weather forecast for any warnings of a first frost, around mid-autumn and just before your normal first frost date. Squash fruits tolerate a light freezing, more than the leaves, but it’s safest to harvest them all before this occurs.

Storing

Bring your squash to the house’s warmest room, ideally for a week, in temperatures above 20 °C/68° F. This hardens the skin and ensures that they are fully dry. After that, keep them anywhere dry and not too cold.

I store squash all winter and often through spring, on windowsills in my conservatory where they are in any sunlight. This does not dry them because they are such a sealed unit. If anything, the flavour sweetens over time.

I find it amazing that some of the Crown Prince, in particular, are still excellent to eat as late as early summer, as you see in the photo below. The flavour was still very good!

These Kabocha squash are saved seed and all were from the same fruit, showing the effect of cross-pollination with Kuri squash

Winter squash keep best in the house, where they can kept be warm and dry; these are Crown Prince and Kuri

Holding last year’s harvest, squash from October of the year before beside new Crown Prince growing on a compost heap in July

Saving seed

Easy to do, too easy sometimes! Seeds are all there to remove, wash and dry when preparing a squash to eat.

The question is, did the fruit’s female flowers receive pollen from a male flower of the same variety? If not you will have an unknown cross between different varieties. The photo above gives some idea, and it was from exactly one Kabocha fruit that I grew such an interesting selection of winter squash!

Cross-pollination does not affect the appearance or flavour of fruits. It does affect the genetic information inside seeds.

One way to be sure of having seed that grows the same as its parent plant is to grow only one squash variety in your garden. Also, there must be no neighbours growing a different variety within maybe 30 m/close to 100 ft, or less if a tall fence is in the flight path between.

To be sure of growing seeds true to variety, you need to hand-pollinate the female flower before any insect does.

Place a paper bag held with a rubber band over a female fruit flower you want to pollinate.
Do this before the flower opens.
Within two to three days, open the bag and rub a male flower of the same variety against the now open female flower.
Re-cover the female flower for two days or so, until it has died. Keep a marker on the fruit, to make sure of harvesting the right one for seed.

See Real Seeds for more information.

Potential problems

‍Slugs damage weak and struggling plants. However, when you are correct with timings of sowing and transplanting, slugs should not be a problem, except in unseasonal weather. It’s hard to foresee this, so it’s wise to keep a few transplants in reserve.

A good rule of propagation is to raise more plants than you need. It’s better to put a few on the compost heap than not to have enough.
Above all, you do not want gaps in the garden during the growing season, such a waste of prime space.

Slug damage to a squash planted too early, in unusually cold and wet weather; we ended up replacing this one

A young plant on 6th June in need of some water; it is rather hot on top of the compost heap

Disease

As I have written above, mildew appears from midsummer and is not a problem for healthy plants. It could be a problem if your plants are not comfortable with your climate. The problem then is the weather, not the mildew! Perhaps your summers are too cold; if so, maybe next year squash need to grow under cover.

Viruses sound bad, but I have yet to see an issue of virus preventing eventual growth. Sometimes the young leaves can be yellow with a viral appearance, yet I find that plants grow out of it to give almost a normal harvest.

Checking for weeds in June 2011 – thanks to no dig it was a quick job!

See the yellow leaves – this is not a deathly virus, but something from the seed; this plant grew greener afterwards and gave a good harvest

And finally

Clear

Often plants clear the leaves dead from mildew and frost themselves, so you just need to rake off the stems which are like straw. Or, if clearing plants while they still have some leaves, twist or cut out the main stem, then you can easily fill a wheelbarrow with the contents of one plant. For a while that fills your whole compost heap, but soon it all diminishes and decomposes in the heap to just a small amount of fibre.

Weeds of squash under cucumber in the polytunnel; they came from homemade compost that had not heated enough, and were not difficult to remove

Broad beans sown after clearing winter squash in November 2011, with a new mulch of old horse manure

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Follow with

Straight after clearing, give your annual dressing of compost or preferred organic matter. Then you could sow or transplant broad beans or garlic. Usually there isn’t time to sow a cover crop, but field beans are possible. Or leave the space empty until first sowings and plantings next spring.

Kuri squash finish earlier, after which we manage to transplant spinach and winter salads. This is in early autumn and often on the same day as we harvest the squash, because every day counts at that time of year

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