How to grow squashes and pumpkins in the UK

Squashes and pumpkins are great plants to grow. You either end up with a decorative pumpkin or a delicious squash (squash is the name that tends to be given to pumpkins you eat), or if you've picked a really good variety, both. However, they have some very specific needs and problems. I'm just going to use the word "squash" in this post, but everything I say applies equally to pumpkins.

Sowing the seeds

In an ideal world, you should sow your squash seeds indoors in April. This gives them an opportunity to grow to a decent size before you harden them off and plant them out. However, they need a lot of light, so make sure they're on a sunny window sill or very near to the window. I usually start mine off on the dining room table. However, this year I was growing an exceptionally large number of plants from seed, and my squash seeds that were at the far end of my plants couldn't cope with the slightly lower level of light and died. So definitely give the seedlings plenty of light. I recommend planting at least 3 times as many seeds as you think you're going to need, unless you know your garden is less dangerous to squash plants than mine (for instance your garden is a balcony – if it is, you will need a truly huge container and canes or a trellis to grow them up, squashes need a lot of space and soil to grow in).

Hardening off and planting out

Once there's no more danger of frost in your area, you can harden them off and plant them out. If you're in London or Cornwall, this will be quite a lot earlier than in other parts of the UK. However, there are problems with planting them out at the earliest possible moment that I've discovered over the years:

1. slugs and snails almost always seem to devour most of the first plants I put out (it's possible this will also be a problem later, but it's also possible that bigger, tougher leaves will deter slugs and snails);
2. if the weather gets a bit cold, your squash will more or less stop growing.

There are, however, also problems with planting them out late:

1. they outgrow their pot;
2. their stem becomes very long, but fragile, meaning it's all too easy to kill the plant by snapping it when finally planting it out;
3. I don't want to have the dining room table covered in plants for any longer than I have to;
4. I don't like leaving my veg beds empty until June, but in an ideal world I wouldn't grow any other sort of veg there first unless it was in the same crop rotation group as my squashes and there are no other suitable veg to put there in my crop rotation scheme.

This means that almost every year, I plant the squashes I've planted indoors out, only to have most of them die either from their stem breaking or from being eaten by snails.

I half solved this problem and half made it worse this year, by allowing self-seeded foxgloves to grow in my squash bed.

It was very pretty and meant I was in less of a rush to plant the squashes. Unfortunately, as there was enough room to plant the squashes and leave the foxgloves, this is what I did. While the weather was dry, the slugs and snails my foxgloves were harbouring only crawled out and devoured one squash plant. Once it started bucketing it down in June, they ventured further afield and stripped almost all the leaves off another two. To get around this, I've now removed the foxgloves and killed all the snails and slugs I found in the process. 

This isn't foolproof. I still have slug rings around the plants. But having the slug rings wasn't foolproof either. Hopefully the combination of these two will work (I choose not to use slug pellets for environmental reasons).

And now we come to the refinements that I will hopefully remember to make next year. With the replacement plants that I started growing the minute I planted my first squashes out, I ended up putting one in the greenhouse and leaving two outdoors. The one in the greenhouse was a little way ahead of the others, but not a huge amount when I put it in there. The difference is now far more obvious:

Maxima squash growing in the greenhouse

Maxima squashes growing outdoors

I am planning to wait until the leaves get bigger and tougher so they are less attractive to slugs and snails before I plant them. Next year, I also plan to leave all my squashes in the greenhouse until at least early June, but potted up into much larger pots than I started them off in.

Also, in order to stop me fretting about empty beds, I've decided to sow annuals that will flower in May in them. This is going to mean sowing the seeds in the autumn. Here's a list of suitable annuals.

Now back to other standard advice for squash:

Feeding

Squash are very hungry plants. Make sure you give them plenty of compost. I'm a big fan of composted horse manure, but for lockdown reasons this year I'm using my own home-made compost. You can just stick this on top of the soil like a mulch instead of digging it in. It will gradually make its way into the soil anyway and will do a perfectly good job of feeding your plants. You can also use chicken manure pellets. I'm not sure if you could get away with just watering with fertiliser. If this is your only option it might be worth a try.

Watering

Squash are also very thirsty plants. Make sure you water them a lot and very regularly. I water mine pretty much every day it doesn't rain. Never water the leaves if you can help it. Squash are very prone to getting powdery mildew and water on the leaves makes them more vulnerable.

Avoiding powdery mildew

Unless you're very lucky, by the end of the summer your squash leaves will be covered in powdery mildew. There are a few things you can do keep it at bay for as long as possible, but avoiding it entirely has been beyond me so far. The tips are:

1. Avoid getting water on the leaves when watering.
2. Check regularly for powdery white spots appearing on either side of the leaves and remove the affected leaves (don't completely strip the plant of leaves, it probably won't survive this, but will survive powdery mildew).
3. Make sure the plants have enough food (compost/fertiliser) and water. A well fed, well watered plant is less susceptible to fungus.
4. Don't grow any other plants prone to powdery mildew nearby (I'm thinking sweet peas here).
5. Support the squash plants on canes or sweet corn (see below).
6. Spray both sides of all the leaves with neem oil diluted with water or milk diluted with water every time it has rained (I tried doing this, but I just can't. The plants get huge, it takes ages and then it only goes and rains again).

Don't worry too much about the plants getting powdery mildew. Mine still produce lovely, edible squashes anyway.

Supporting the plant

Squashes have a natural tendency to climb - some more than others. If you grow sweet corn within their reach, a lot of squashes will use their tendrils to climb up it. This keeps them off the ground and seems to lower their risk of powdery mildew. You can also insert bamboo canes in the ground around the squashes, either just upright or in groups tied together at the top. Some varieties of squash will naturally grab these with their tendrils, some need tying on. If your squash plant grows really big fruit, then you may need to either provide it with much sturdier support than bamboo canes or simply let it rest on the ground. I cannot guarantee that every type of squash will take well to being treated as a climbing plant, but the ones that like it really like it. I can say for certain that winter squash Sweet Dumpling is happier climbing up something than sprawling across the ground. This year I'm growing Maxima squashes and I'm not yet sure how it will go with them (or indeed if I have enough bamboo canes left to try this).

Harvesting and curing

Summer squashes can be harvested throughout the summer. Winter squashes are typically harvested in autumn, especially in October. A lot undergo a colour change that shows they are ripe. Ideally, you should wait for this colour change before harvesting them. Other signs they are mature is a tough skin and a hollow sound when tapped. However, irrespective of whether they have achieved this, squashes need harvesting before the frosts come. In my experience with winter squash Sweet Dumpling, some will not change colour before you need to harvest them, but may then change colour much later after harvesting.

To harvest them, cut the stalk with secateurs, leaving as much stalk as possible attached to the squash. Do not lift them by stalk, as you're likely to damage the fruit

Once you've removed the squash, let them cure outdoors in the sunlight for about seven to ten days. If frost is expected, cover them with cardboard or straw at night. Alternatively you can instead leave them to cure in a greenhouse, polytunnel or cold frame. They will become well-ripened here. If you accidentally slightly damage the skin, don't worry: any wounds will heal. But do make sure the fruits don't touch each other.

Storage

Ideally, winter squashes should be stored in a well-ventilated position at between 10 and 15°C. In practice, I don't have any such storage facility. Under the stairs is probably the nearest I have to this, but they're difficult to access and check for signs of rot there. Actually I have successfully stored a lot of squash (particularly winter squash Sweet Dumpling) in the dining room at room temperature. I've also had some disasters though, as when they rot they turn to putrid, staining mush surprisingly quickly. For this reason I now store them on plastic Ikea trays that I can wipe clean if they rot instead of letting them stain the dining room table. Do watch for signs of rot, and remove any affected fruit immediately

Some varieties can happily be stored for up to six months. You'll find out by watching for rot! If you look like you've picked a variety that won't store well in your conditions, you can always roast it and then freeze the roasted flesh. I find this freezes well.