Key takeaways
- Record-breaking vegetables start from pedigree seed or pips passed between growers
- Giant pumpkins need a bed several metres across, lots of water and daily care
- Show onions are sown around Christmas under heat for September shows
- Pot leeks are grown from pips and judged on the size of the blanched stem
- See the giants at the Harrogate and Malvern autumn shows in September
- Start with one giant class at your local show rather than chasing a record
Giant vegetable growing is the gloriously over-the-top corner of the hobby, where one pumpkin can outweigh a small car. UK growers have set world records for some of the heaviest and longest vegetables ever grown, and the autumn shows are packed with people who come to gawp.
This guide explains how the champions do it, where to see the giants and how to have a go yourself. If you’d rather grow vegetables to win on looks and quality, our guide to show growing for your village veg show covers the regular classes.
What makes a giant vegetable different?
Champion vegetables aren’t ordinary crops left to grow longer. Growers stack every advantage they can, and four things matter most.
Pedigree seed. Champion seed comes from plants that have already grown huge. Giant pumpkin seed is listed by the weight of the fruit it came from. Onion and leek growers keep their own lines and swap them with trusted friends.
Deep, rich beds. Beds are dug deep and filled with plenty of well-rotted manure and compost, often months before planting. Long carrots grow in containers of sieved compost or sand, as any stone makes the root fork.
Protection from checks. Many giants start under glass with gentle heat. Growers avoid anything that stops growth, such as cold, drought or pests, because a plant that stalls rarely catches up.
Daily care. Serious growers check their plants every day through the season. They water, feed, measure and watch for trouble. This is the part newcomers most often underestimate.
How do growers raise giant pumpkins?
Nearly every giant pumpkin is the Atlantic Giant type, bred from the line developed by Howard Dill in Nova Scotia. Growers buy seed with a known pedigree, often through pumpkin clubs and seed exchanges.
One plant, one fruit and a bed all to itself. Growers measure every day to check the pumpkin is still piling on weight.
Sowing: In late April, indoors with heat. Pot on as soon as the roots fill the pot.
Planting out: After the last frost, under a cloche or temporary shelter at first. One plant gets a big bed to itself, several metres each way.
Choosing the fruit: Growers hand-pollinate a few female flowers on the main vine, then keep just one fruit. All the plant’s energy goes into it.
Care: Lots of water, regular feeding and shade over the fruit on hot days. The vines are trained out flat and pinned down so they root along their length.
Show day: Lifting a giant pumpkin needs slings, several people and often a pallet truck. A crack or soft spot can rule it out of the weigh-in, so the journey is nerve-racking.
For ordinary-sized pumpkins and squash, see our guide on how to grow pumpkins and squash. Big marrows follow a similar routine on a smaller scale, as our guide on how to grow marrows explains.
How are giant show onions grown?
Giant onions are all about a long season. Growers sow around Christmas or New Year in a heated propagator, so the plants have time to bulk up before the September shows.
Exhibition strains such as ‘Kelsae’ and ‘Robinson’s Mammoth’ are the usual choices. Seedlings are potted on as they grow, then planted into a rich bed, often under glass. Regular feeding and steady watering keep them growing without a check. As the bulbs get heavy, some growers support them with soft slings so they keep their shape.
At the show, onions are cleaned and dressed, with the neck neatly tied. Giant classes are judged on weight, and damaged or soft bulbs get marked down. Our guide to exhibition onions covers the smaller, quality-judged onion classes.
A giant show onion dressed for the bench. These need a head start from Christmas to get this big by September.
Pot leeks: the North East tradition
Pot leeks are short, fat leeks judged on the volume of their blanched white stem. They’re a proud tradition in North East England, where clubs have held leek shows for generations.
Pot leeks are short and fat. Collars keep the stem white, and that blanched part is what the judges measure.
Pot leeks are grown from pips. These are small bulbils that form on the flowerhead of a show leek after the flowers are removed. Each pip grows into an exact copy of its parent, so good lines are kept going for years and closely guarded.
The leeks grow in deep, rich beds, often under cover. Growers blanch the stem with collars or tubes to keep it white. Our guide on how to grow pot leeks for show walks through the season.
Long carrots and parsnips for show
Long carrots and parsnips are judged on length, so the root must come out of the ground in one piece, right down to the thin tip.
Long carrots are grown in drums of sieved compost. The thin tip counts, so it has to come out in one piece.
Growers fill tall drums or pipes with sieved compost or sand, then bore a hole down the middle and fill it with a fine mix. Seed is sown at the top in spring and thinned to one plant. Lifting is the tense part: the container is washed or tipped away gently so the long, thin root doesn’t snap.
Our guide to long carrots for show explains the method step by step.
Where to see giant vegetables in the UK
Autumn is giant vegetable season. These shows have big giant vegetable displays:
| Show | Where | When |
|---|---|---|
| Harrogate Autumn Flower Show | Great Yorkshire Showground, Harrogate | Mid-September |
| Malvern Autumn Show | Three Counties Showground, Malvern | Late September |
| County and village shows | All over the UK | August to September |
Check each show’s website for this year’s dates and classes before you travel. Growers are usually happy to chat about their giants, and you’ll learn a lot just by asking.
Village shows often have a heaviest marrow or biggest onion class. It’s a friendly way to have your first go.
How to try a giant class at your local show
You don’t need to chase a world record to have fun with giants. Here’s how to start.
A heaviest marrow class is a fun first giant. One plant, one fruit and plenty of water does the job.
- Find a local show with a giant class, such as heaviest marrow or biggest onion. Village and allotment shows often have one.
- Read the schedule carefully. It says exactly what to bring and when to stage it.
- Pick one class. Grow two or three plants in your richest soil and take the biggest.
- Water and feed steadily. Big vegetables need a lot of both, without stopping and starting.
- Stay for the judging. Chatting to other growers and the judges teaches you more than any book.
To see how judges score the classes, read our guide to allotment show judging. There are more crop guides in our growing section.
Common mistakes with giant vegetables
- Ordinary seed. Normal pumpkin or onion seed won’t grow giants however well you treat it. Get seed from a proven line.
- Too many fruit. Leaving several pumpkins or marrows on one plant splits the energy. Keep one.
- Uneven watering. Dry spells followed by soaking can split fruit and bulbs.
- Planting out too early. Cold nights check pumpkins and marrows, and they rarely recover their pace.
- Rough handling on show day. A cracked or bruised giant can be marked down or ruled out.
Once you’ve caught the bug, our guide to show runner beans is a good next class to try.
Frequently asked questions
What is the world record for the heaviest pumpkin?
In 2023 Travis Gienger in Minnesota set it with a pumpkin of about 1,247kg. Records are broken often, so check the Great Pumpkin Commonwealth for the latest figure. Almost all record pumpkins are the Atlantic Giant type.
How long does it take to grow a giant pumpkin in the UK?
Around five months from sowing to the autumn shows. Most growers sow indoors in late April and plant out after the last frost. Sowing too early leaves plants stuck in pots, and sowing too late gives the fruit too little time to swell.
What seeds do champion vegetable growers use?
They use pedigree seed from proven winning plants. Giant pumpkin seed is listed by the weight of its parent fruit. Onion and leek growers swap seed and pips through specialist societies and shows, so joining one is the best way in.
Where can I see giant vegetables on display in the UK?
The Harrogate and Malvern autumn shows are the best places to see them. Harrogate’s Autumn Flower Show runs in mid-September and Malvern’s Autumn Show in late September. Many county and village shows also have giant vegetable classes.
Can I grow giant vegetables on a normal allotment?
Yes, some giant classes fit on a normal plot. Big marrows, show onions and long carrots need only a corner. A record-chasing pumpkin is harder, as one plant needs a large bed and daily attention.
Can you eat giant vegetables?
Most can be eaten, but they rarely taste good. Giant pumpkins and marrows are watery and coarse, and huge onions are mild and soft. Growers grow them for the weigh-in, not the kitchen.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
