How I Grew the Heaviest Outdoor-Grown Pumpkin in the UK
Growing giant pumpkins requires dedication, but a little bit of gardening knowledge goes a long way. In spring 2016 I was a giant pumpkin novice, by October I could lay claim to a UK record. Here’s how I did it.
I started off by consuming as much information as possible. The Giant Veg Community is a great place for help and advice, but I also scoured bigpumpkins.com and got my hands on a couple of Don Langevin’s ‘How to Grow World Class Giant Pumpkins…’ books. These were an invaluable guide through the summer and the amount of information available to novice pumpkin growers is huge in comparison to other giant veg.
To stand a chance at growing anything over a couple of hundred pounds, you have to get the right seed. Normal ‘Atlantic Giant’ from the garden centre just won’t cut it. You need to source pedigree Atlantic Giant seed from other growers if you want anything over 300lbs. I struck lucky and was given the opportunity to grow the 2096 Meier, which sold for a world record price (£1,250!) at auction in spring 2016. Don’t worry, you don’t have to spend that kind of money. Seed with excellent genetics is widely available at more affordable prices (just not at your local garden centre).
Giant pumpkins make big plants and take up a lot of space. I gave my plant a patch measuring 30ft wide by 40ft long (1200sq ft). In hindsight this is a bit too much. Don’t worry if you don’t have that kind of space, pumpkins weighing 800lb have been grown in patches just 10ft x 15ft in size.
When I started the ground had been a neglected field for over a decade. In the autumn I dug it over to about one spit (a spades depth) deep, turning in all of the grass and weeds. My soil is heavy clay so I leave it exposed to winter weather; this allows the frost to get into the clods and break them up. In the spring I covered the patch with garden compost about 2” deep, before rotavating it in, helping to break the soil up further. Compost is the key; it boosts the fertility of the ground and improves drainage alongside its ability to hold moisture. Another layer of garden was put on in the late spring as a mulch. This is not normal practice but it worked wonders keeping the weeds down.
In the area where I was going to plant the giant pumpkin, I double dug (2 spits deep) an 8ft x 8ft square. This was to improve drainage in the area where the main roots would be. Pumpkins do not like sitting wet. I dug in sandy grit in this square to improve the drainage further.
I also surrounded the patch with green wind netting, to about 4ft high. I garden on top of a hill, which can be very windswept. Strong winds and large pumpkin leaves do not go well together and I knew this would be the greatest danger on my patch. This is the trade off I made in order to have a patch that faced south and benefitted from full sun all day, with nothing to cast a shadow.
It is important to have your soil tested. I sent samples off in early spring. This gave me enough time to correct anything I thought was wrong before planting. Thankfully, clay soils are naturally fertile and I didn’t have to make any changes or apply lots of fertiliser. A pH of anything outside 6.2-7.2 would probably be enough to get me thinking. Anything between 6.5-7 is ideal.
To grow a giant, it is said that you need about 90 days leaf growth and 90 days fruit growth. With the weigh off in early October, this meant I had to start in mid-April. The best way to germinate the seed is to soak it for a few hours in lukewarm water (20-30c). You can add a bit of liquid seaweed too (I use Maxicrop). Some growers will file the edge of the seed with a nail file or fine sandpaper to improve water uptake. DO NOT FILE THE POINTY END- this is where the root emerges from. After soaking, put the seed in damp kitchen paper, then inside a sealed freezer bag. Rather than the freezer, then put this somewhere warm (no hotter than 30c). An electric propagator is ideal, if not the airing cupboard makes a good substitute! If conditions are right, you should see a root emerging from the seed within 36 hours. Or, if you’re a novice like I was, don’t do any of this, just stick ‘em the potting compost and wait! I paid the price for this, and lost some of my seeds to rot.
I pot the seeds into a 4.5litre (1 gallon) pot. I use a potting compost called Sylvamix (this is peat free, very free draining and low in nutrients), mixed with perlite (about 50/50) to improve the drainage. The compost needs to be moist, but not dripping wet. It also helps that it’s not freezing cold. Get the compost up to temperature the day before hand. Put the seeds (pointy end first) a centimetre or so under the surface. Do not press them in. Put the pots in a propagator set no higher than 30c, or the warmest, sunniest windowsill you have. Don’t be tempted to water, the moisture from the soaking should be enough to get the seedling to emerge, and they hate sitting wet (did I mention that already?!) They should be up in 3-5 days.
Once germinated, the plants need to be taken out of the propagator, away from direct heat. If you can stop them experiencing night time temperatures below 10c, so much the better. If you have grow lights, use them, it will really help, but don’t give them more than 14-16 hours of light per day. Once the first true leaf appears, you should be getting ready to plant them out, usually this will be early May. This is where my path differs from other growers. In the UK, it is common practice to grow giant pumpkins in a glasshouse or polytunnel. This means they are protected from cold nights and possible late frosts during April and May. Not many of us have this luxury, me included. To overcome this problem I built a cloche covered in clear polythene, measuring 3m x 2m. This was positioned over the plant until it had outgrown it. When this stage is reached, further wind netting is erected around the plant, which is moved as the plant gets bigger. Don’t position it so close that it casts shade though. On sunny spring days I had to open ends of the cloche to stop the plant from overheating, at night I covered the plants with horticultural fleece to keep them warm. In the future I hope to use soil warming cables and heaters in the cloche to speed up early season growth. If you can’t give the plants this protection, delay sowing your seeds until you can plant them out after the last chance of frost. Beware though, as doing this will give you a shorter growing season in which to produce a heavyweight monster.
The main vine of the plant will grow opposite the first true leaf, so put the plant in the ground with this leaf facing straight down the middle of the patch. Again, don’t firm the plant in too much. Use another sprinkling of mycorrhiza in the planting hole and on the plant roots at planting time.
Training, Pruning & Vine Burying
If conditions are good, the plant will grow rapidly, and growth must be controlled. It is best to train the main vine down the middle of the patch. Sideshoots (secondaries) should be trained perpendicular to the main vine, towards the edges of the patch. This is what is called the ‘Christmas Tree’ pattern. You will understand once you start doing it! Any sideshoots on the sideshoots (tertiaries) should be completely removed, you don’t need them and they will just make everything a congested mess. Be careful not to remove the immature flowers that form at the same place (bottom of each leaf), you will need these in a few weeks time.
A useful trait that pumpkins have that growers can exploit is the fact that the plants will send out roots at the bottom of every leaf. By encouraging this to take place the plant can be rooted across the entire patch, pinning the plant to the ground (making it less susceptible to wind damage) and giving it the ability to take up more water and nutrients. To help this process along vine burying needs to take place. This can be as simple as scooping soil over the base of each leaf, or completely burying the entire vine in soil. I used a method developed by Ian & Stuart Paton (the UK record holders), which involves filling 3 litre pots with compost, getting them sodden through, then placing them upside down over each leaf node. Whatever method used, the basic idea is to block out light to the base of the leaf, encouraging roots to develop. If you are really lucky, you can get three to form at each node; one underneath and one either side of the leaf. A sprinkling of mycorrhizal fungi in these areas will help to inoculate these new roots.
Through May and June the main aim is to encourage as much leafy growth as possible, this will provide a big ‘engine’ to fuel rapid fruit growth once pollination has taken place (leaf growth behind the fruit is the main driver for fruit growth, leaf growth after the pumpkin less so). If things are going well you will have to carry out vine burying a couple of times a week to keep up. It’s at this stage the plant will require feeds that are higher in nitrogen. I used dried blood (bloodmeal), an organic choice. This is 12% nitrogen and comes from abattoirs. It is fast acting and water soluble so can be applied as a granular feed or liquid. Be careful not to get it all over the leaves, as they may scorch. As with all things, moderation is best, too much will make the plants bloated, soft and vulnerable to pest and disease attack
The aim is to try and get a female flower to appear on the main vine, between 10-15ft away from the stump, between 21st June and 7th July. This will give you enough days of the growing season left for maximum fruit growth. I scrapped in by the skin of my teeth and pollinated on the morning of the 7th! Any closer to the stump and there will not be sufficient leaf growth to fuel rapid swelling of the fruit, any further away and you will probably have to delay pollination and lose precious growing days.
It is important to be able to tell male and female flowers apart. Male pumpkin flowers have long stalks, and held a few inches away from the stem. Female flowers lack this stalk, being positioned much closer to the stem, and have a small, immature, un-pollinated pumpkin (about the size of a marble) at their base. A keen eye is needed to tell when the female flower is about to open. The evening before opening the petals will swell and will just begin to prize open at the tip. It will open early the next morning (about 4am!) so you need to be ready. Most growers will hand pollinate themselves, in order to pollinate the flower with pollen from a known parent. This is only important if you value the seeds forming inside your pumpkin and what them to produce giants too. If not you can leave the pollination to the bees. Be warned though, anything in the cucurbit family is extremely promiscuous and your giant pumpkin could be pollinated by a bee that’s just visited your neighbours courgette plants!
To stop the bees getting there first, I tie the female flowers shut with twine the evening before they are due to open. Placing plastic cups over them also works. Also that evening, cut some male flowers that will open the next day (so the unopened ones- keep them in a glass of water indoors overnight) from whatever plant you want to pollinate with. You can use the male flowers from the same plant you are pollinating (this is called ‘selfing’ and keeps the genetics pure). I used male flowers from another giant pumpkin plant, so the 2096 Meier (female) was pollinated with the 1998.5 Jutras (male).
It is best to pollinate first thing in the morning, anytime between 5am-10am, before the heat of the day kicks in. Untie the female flower and let it open up. That one flower can only be pollinated for a few hours on the day it opens, so don’t leave it. Take the male flowers and remove the petals from it, leaving yourself with a stalk with a stamen on the end covered in yellow pollen. Using it like a paintbrush, dab this pollen all over the lobes inside the female flower. Use multiple male flowers to ensure good pollination. Then tie the female flower shut again (to keep out the bees and pollen beetles) and if it’s hot cover the flower with a tea towel. Pollination is much better if you can keep the flower out of direct heat. You may want to pollinate two or three flowers over the course of a week or two on the main vine to ensure you get at least one that sets. Ultimately though, it’s one plant=one pumpkin if growing for size.
Positioning the Fruit
When the pumpkin is small and young, it’s the perfect time to get it placed properly. You need to get the fruit positioned perpendicular to the vine. This will lessen the chance of the ‘shoulders’ of the fruit pressing against the vine it is attached to as it grows, potentially snapping itself off the plant. Make small adjustments each day, preferably at the hottest time of day when the stems are at their most supple, until the ideal position is reached. I placed a sheet of plywood (which had been covered in black plastic) underneath the fruit, with a layer of kiln dried sand between the board and the fruit. The sand allows the pumpkin to slide and swell easily, reducing the chance of it developing a concave underside and therefore weighing less. When growing its quickest, the fruit made ripples in this sand, amazing! You should also aim to keep the stem end and blossom end of the fruit as parallel to the ground as possible. The board gives you the ability to adjust the position of the pumpkin when it reaches a size so massive it’s no longer possible to move it by hand.
Once pollination has occurred, that’s when the importance of watering correctly really matters. I water my plants using leaky hose laid out across the patch, each hose spaced about 30” apart. They would need to be closer if I had sandy soil. I am incredibly lucky and can connect this to a watering system in the garden that pumps reservoir water out at about 7 bar. If using tap water, it is advisable to fill up water butts the day before, partly to let the chlorine disappear but also to let it warm up a bit. The aim is to give the plant about 1” of water per week, which includes natural rainfall. I watered my plants every day, at the same time of day, for the same length of time, giving them the same amount of water. I believe this consistency was key to my success. I was aiming to keep the ground moist, but not sodden. I hope to improve the accuracy of my watering this year to measure exactly how much water I put on each day. Erratic watering can spell disaster for giant pumpkins, if they go without for an extended period, growth will slow and the fruit will begin to harden. If they then get a deluge, the plant will take it all up, but the fruit won’t be able to expand and will split; just like tomatoes do. Little and often is best. Cross your fingers and hope to avoid summer downpours, this is one of the biggest dangers of growing outdoors.
Once the fruit begins to grow, huge demands are put upon the plant to sustain that growth. These need to be managed to keep the pumpkin growing smoothly. I fed my plant with Maxicrop Tomato feed (5.1:5.1:6.7), basically changing from a higher nitrogen feed to a higher potassium one. Again, little and often was the method, but much more often than it says on the bottle! My plants got two liquid feeds at the main roots each week (2 gallons watering can each time) and one foliar spray a week. I like to use balanced feeds like Maxicrop, rather than fertilisers that are really high in one particular nutrient (such as Miracle-Gro). The plants were showing signs of magnesium deficiency (yellowing of the leaves) so they got a weekly foliar spray of Epsom Salts (magnesium sulphate) to cure this. They also got sprayed once a week with a product called SB Plant Invigorator. This isn’t a feed as such, but more of a plant health tonic. The main reason to use it was that it helps control sap sucking insects (aphids) and shows some control on powdery mildew (which is public enemy number one when it comes to growing giant pumpkins).
The Push to Weigh Off
Once pollination has occurred, it really is just a matter of keeping the plant healthy, giving it everything it needs to put on maximum fruit growth and being consistent with everything. Don’t treat your plant erratically, and if something is not quite right, don’t just act on a whim without thinking. You know what they say about record breaking; dedication is what you need, and this includes trying to break personal bests. Anything that’s not perfect will need addressing quickly, but stop and think about what to do instead of acting quickly and making a mistake. I made the mistake of going to the patch on a hot summers day in mid-afternoon (it was +30c) to find a plant with wilting leaves and sagging growing tips. In my hurry to cool the plant down I got the hose out but ended up scorching all of the growing tips. I should have waited for the hot weather to pass.
The pumpkin will grow slowly for the first week or two, but will then suddenly take off. It pays to measure this growth to keep an eye on how fast the fruit is growing. This is called taking an Over-The-Top (OTT) measurement. To do this, three measurements of the fruit are needed. Using a tape measure (you will need a big one eventually!) measure the pumpkin from side to side from ground level. Then do the same measurement from stem end to blossom end, from ground level. Lastly, measure the circumference of the fruit at its widest point, but try and keep the tape measure parallel to the ground. Add these three measurements together, which you can then compare to the OTT chart (available on the Great Pumpkin Commonwealth website) to give you an estimated weight for your pumpkin. At the very least, you need to do this once a week to track weekly weight gains. This is how my record pumpkin performed:
7th July: Pollination
29th July: 121lb
4th August: 236lb (+115lb)
11th August: 437lb (+201lb)
18th August: 661lb (+224lb)
25th August: 868lb (+207lb)
1st September: 1047lb (+179lb)
8th September: 1166lb (+119lb)
15th September: 1247lb (+82lb)
22nd September: 1296lb (+55lb)
29th September: 1317lb (+21lb)
8th October: 1333.8lb (+16.8lb)
Just remember, if you grow anything upwards of 500lb, you will need at least half a dozen strong people to lift it, with a large piece of material underneath it. Anything over 1000lb and you will need a machine! Final job of the season is get to a weigh off or giant veg show, see what you have achieved, enjoy yourself, get chatting to other growers and get planning for next year.