Growing Pumpkins in Tasmania

Growing Pumpkins in Tasmania.

Pumpkins are a favourite for the veggie gardener and feels like a sign of achievement in the middle of winter when you have a pantry ladened of big sweet pumpkins. But Tasmania is a marginal climate for these warm weather lovers. By this I mean that our summer growing season is short and that depending on the season, we either have just enough or not enough time to get those fruits ripening before cool frosty weather arrives.

You can sow pumpkins in the garden in spring when all danger of frost has passed and the soil temperature has reached at least 18°C. Night time temperatures should be over 10C regularly – rarely achieved before December in many Tasmanian regions.

I prefer to start the seeds indoors around the last frost date (around mid-October where I am in the Huon Valley on average). This means they are planted out around the end of the first week of November (3 weeks from sowing to planting). I have grown adequate tasting pumpkins when planted by mid-December so we have this time gap to get them going. My heat mat is set to 22 when germinating pumpkin seeds. A good balance for me as I have many other veg also on the same hotbed. A window ledge should suffice inside, just get them sun once they pop up so they do not get as leggy. They get leggy as the amount of sunlight they receive is too low compared to the average temperature they feel over the day.

Pumpkins grow best in a sunny spot in friable, free-draining soil rich in organic matter. Add aged compost to planting beds in advance of sowing (I generally top all my beds up with compost in July/August).

At planting I place a mound of cow manure and plant the single plant from its pot into that, no need to disturb the roots. I also lay black plastic down on the ground to ensure higher soil temperatures as we are in a cool climate. This can be ignored if the season is warm and you are confident of sunny warmer days up to x-mas. Not what we have achieved the past 3 seasons.

I prefer to not dig over the soil as it breaks the soils water holding ability. Having soil that holds moisture during dry times is an advantage after x-mas when we usually get warmer and drier conditions.

You can direct seed pumpkins into the mound of manure, just note that the ideal soil temperature is 21 C, so you may be waiting till later November in many seasons at the earliest. Some areas of Tasmania will be warmer so direct seeding is a viable option most years (I prefer the seedling route to maximise my growing season – Hobart are areas with warmer nights may have an extra 2 to 3 weeks growing season).

Once planted and the black plastic is down, be prepared to cover the seedlings if a cold spell hits (As it did while writing this). Below is a photo of fleece over wire which takes 5 minutes to erect to offer protection from nasty cold weather. I believe Bunnings and the like have ag fleece.

Varieties:

There are many varieties to grow. In a short growing season, Golden Nugget is a reliable performer which is a smaller bush. Personally, not my favourite for flavour in mid-winter, but quite nice a few weeks after picking. I also really like the buttercup styles like Delica F1 or buttercup. Of the larger winter pumpkins, I often have grown Qld Blue, Jarrahdale but my favourite is Sweet Grey F1. It is a hybrid with early maturing tendencies and handles more volatiles conditions well. It is also a quick germinator which helps in our volatile springs. It produces lovely sweet flesh in winter soups or baking dishes. There are many options for the gardener to try each year and I have not grown all that is out there. A few years back during a very warm summer, I grew Musquee de Provence which was nice. However, given the cooler summers of 2020 to now, I have opted for reliability. I am growing seed collected of Sweet Grey in the hope to debybridise it in the future so we can save its seed reliably, but these things take time.

One recommendation is to ensure you space the pumpkins adequately. If 1m is recommended, then go 1m. If you go closer, be prepared to water lots to ensure adequate soil moisture.

How many should you grow? I look at it as 1 plant minimum per person in the house, 2 ideally. So, for two people I would plant 4 plants. The large vining plants will give probably 2 good sized pumpkins each, 3 if you do well.

Often, I get asked at market why are my flowers not forming fruit. They turn black and fall off. This is a pollination issue, or lack thereof. The first flowers will be male flowers (no mini pumpkin at the base of the flower). Around a week after seeing male flowers, you should see female flowers. These flowers must be pollinated by bees and beneficials by moving pollen from the male to the female. So, get the cosmos, marigolds and other flowering plants (hyssop and lemon balm is great) to help out.

If you’re struggling to see the pollinators or concerned, you can do it yourself to ensure those few pumpkins (Or to ensure no cross pollination from other varieties if you want to save the seed). Use a small art brush to collect pollen from a male flower then brush the pollen onto the centre of the female flower. Or break off a male flower, tear off the petals and then insert into the female flower! Best done in the morning also, as the flowers tend to close up later. The are many ways to do this, these are just how I do it.

Outside of the initial compost and manure, I really only fertilise with 3 weekly seasol until x-mas. Then I give the plants a side dressing of rock mineral (phosphorus) and some powerfeed with the seasol each 3 weeks. And ensure the soil is kept most. Slow and deep watering is better than short sharp ones.

As the trailing vines grow, I pinch the ends off when they have 6 or so leaves on them. This encourages side shoots and more male and female flowers. Once my large vining winter pumpkins have 3 fruits on them, I pinch the rest off the vine with no fruits on them. This is to help those 3 get large and stop the plant trying to share the load. It is hard to know if summer will be wrm enough to get more per plant. You can leave more fruits on and fingers crossed they mature in time to have that lovely sweet flesh in winter. 

How do you know your pumpkin is ready to harvest? I wait till the connection stalk to the pumpkin looks to be dead or shrivelled a bit. Keep an eye on it and you will see it change. That is when I leave 15cm either side of the vine connected when I cut it off. Give it a wipe over and store in a dry place. I have a studio where they sit on a ping pong table before going into the kitchen pantry.

Hopefully this helps you in some way. The biggest tip I can really say is get that black plastic down to keep soil temperatures higher (Especially useful for Waltham Butternut – a real heat lover). You will be rewarded, especially when the spring is cold as it has been.

Happy Growing

Dave