Grow a giant pumpkin

Information sheet

Learn how to grow a giant pumpkin. Get top tips from record breaking outdoor pumpkin grower and RHS fruit and vegetable expert, Matthew Oliver. 

  • School term: Early Autumn, Late Autumn, Late Spring, Early Summer, Late Summer
  • Level of experience: No experience needed
  • Subject(s):

A month-by-month guide to growing a monster pumpkin!

Start by purchasing giant pumpkin seeds from a seed supplier. Some good ones are ‘Atlantic Giant’, ‘Wallace’s Whoppers’ or ‘Paton Twins Giant’. These are all genetically huge pumpkin varieties and are perfect for growing yourself a monster!


  • In the winter before you begin this project, or at least 6 weeks before planting, you should aim to improve the soil in the area in which you plan to grow your pumpkin.
  • You can do this by digging in ‘well-rotted’ manure or green waste (garden compost), or by adding soil improver. Pumpkins are hungry fruits and this will add the nutrients needed, as well as provide the best soil structure - increasing your chance of growing a monster!
  • Our soils’ resources on digging clay and sandy soils can advise the best treatment for particular soil types.

See our ‘Pumpkin crop sheet’ for details on how to sow and grow your pumpkin plant. Below is additional month by month advice for growing a giant!


  • Giant pumpkin seeds are larger than normal pumpkin seeds so before sowing, soak them for an hour or two in tepid water (20-30°C)
  • Sow a couple of seeds pointy end down into a light, free-draining compost.
  • Do not overwater! Pumpkins hate being cold and wet. The number one error for beginners is overwatering seeds before they germinate, which causes them to rot. Moisten the compost and don’t water it again until the surface has dried off.
  • To encourage germination, keep the seeds somewhere warm and light (25-30°C is ideal). Your seedlings should start to appear within 3-7 days.


  • Pumpkins grow VERY quickly. Transfer your seedlings into a bigger pot as soon as possible - you’ll be amazed at how the roots fill the new space.
  • If all your seeds have germinated, this is the point to decide on the best one to keep (monster pumpkins take up a LOT of space!). You could grow them all and host a competition to see which will be the biggest!
  • Plant your seedlings outdoors from mid to late May, the more outdoor space you have the better.
  • Keep plants warm, especially at night. If possible cover them with a cloche or horticultural fleece during cold spells.


  • The aim now is to grow as many leaves as possible! Give your plants a high-nitrogen liquid feed which encourages growth of green leaves. These leaves will fuel the growth of the pumpkin once it starts to grow and continue to feed it until they die off in the autumn.


  • Yellow flowers will start to appear on your plant, look for a female one. Female flowers have a small pumpkin at their base and only have stigma. See our Flower structure diagram to help you identify this flower.
  • Choose a female flower on the main vine as far away from the stump of the plant as possible. This is where your pumpkin will form. You can let the bees pollinate the flowers for you, or you can do it yourself by remove some male flowers and using them as a paintbrush to dab the pollen onto the centre of newly-opened female flowers.
  • Wait until more than one flower has been pollinated and then see which pumpkin gets off to the best start, then removing the rest. Your pumpkin will grow far bigger if you only have one fruit on the plant!
  • Once your plant has been pollinated and fruit has started to develop behind the flowers, you can begin to give a high potassium feed, such as tomato food.
  • Water regularly from now on - every day if you possibly can!


  • If you are measuring your pumpkin be careful not to damage it as the skin is delicate and any scratches will cause a scar that could affect the overall size.


  • Look after the plant and keep it healthy. Continue watering and feeding until the end of the month.
  • Calculate and record your final estimated weight. If your pumpkin reaches 45kg, you’re doing really well. If you manage to grow anything bigger than 136kg, you’re on to something!


  • Let the fruit mature and colour on the plant and remove before the first frost strikes. If storing, allow skins to harden in the sun.

Matthew’s Top Tips

  • Plant your seedlings with the first true leaf facing the direction you want the plants to grow in, as the main vine grows away from this leaf. The first true leaf appears after the two seed leaves.
  • If you are feeling keen, scoop up a bit of soil with your hands and bury the stems at the bottom of every leaf. This will encourage more roots to form, anchor the plant to the ground, and let it take up more water and nutrients – all helping to grow a bigger pumpkin!
  • For maximum size, cover your developing pumpkin with a white sheet. This will keep the sun off and stop it from ripening too quickly
  • Keep watering the plant regularly. If you’ve got everything right, you will be amazed at how quickly the fruit grows
  • Gardeners who are looking for a “prize for size” pumpkin might select the two or three prime candidates and remove all other fruit and vines.

More Top Tips

  • Pumpkins can be prone to rotting if they are sitting on wet ground. If necessary you can raise the fruits off of the ground using a wooden board.
  • When growing pumpkins you can help the fruits to ripen by removing any foliage that is shading them.
  • You may need to harvest pumpkins a few weeks before Halloween and bring them into a warm room to help them ripen in time.

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