Lucy holding some giant carrots

How to Sow and Grow Giant Carrots

If you’re reading this blog you’ve decided to take the plunge and grow the amazing Japanese carrot variety ‘Manpukuji’. This super rare 400 year old Japanese carrot from the Edo region of Japan naturally grows very large and is therefore perfect for taking first prize at the county fair. However, unlike many giant carrot varieties, Manpukuji also remain tender and delicious up to a very large size making them an excellent culinary variety as well. We will share our hints and tips on how to grow these carrots that could similarly apply to any giant competition strain carrot growing.  With minimal effort Manpukuji will easily reach 75cm – 1m long and still remain tender to eat. However for the real giant veg fans, some extra effort can get these whoppers to grow up to 1.5m in length! Once grown, if you’re wondering what to do with them, try our salt baked carrots recipe to give them the respect in the kitchen they deserve!

How to Sow and Grow Giant Carrots

Materials you’ll need to grow carrots:

  • Giant Carrot seeds
  • Old peat free compost – perfect way reuse old container compost
  • Sand
  • Trowel
  • Watering can
  • A deep trough or container such as a dustbin, or if you’re really keen – sections of drain pipe cut to 1.5m lengths
How to Sow and Grow Giant Carrots

Sowing carrot seeds:

Prepare the Soil:

Ensure your soil is well-draining and free from lumps and large stones that can hinder carrot growth. Carrots thrive in loose, sandy soil. The best way to achieve this is a roughly 50/50 mix of compost and sand. Carrots also prefer low nutrient compost, nutrient rich soils can make them branch rather than growing as one long straight root. This is therefore a great opportunity to reuse old compost from containers that you wish to refresh. If the compost has been grown in for a season already it will be perfect for carrots.

Choose the Right Time:

Carrots can be sown directly outdoors from March to July, depending on your location in the UK. Aim for a time when the soil is workable and not too wet. Carrot seeds can take up to 14-21 days to germinate, so plan accordingly. This plant hates to be transplanted so never start your carrots in module trays, always direct sow.

Sow the Seeds:

Plant carrot seeds in shallow furrows, spacing them according to the variety’s recommendations (usually 5cm apart but for this larger variety give them 15cm). Cover the seeds lightly with soil and water gently, you are aiming to sow them roughly 1cm deep. For the serious growers out there that want the longest possible carrots, you could grow individual carrots in lengths of drain pipe filled with the same soil mix as your container. Make sure the soil in the pipes stays moist but there is no need to water excessively except in very dry periods in summer.

Thin Out Seedlings:

Once the seedlings emerge, thin them to ensure proper spacing – if you’re using the drain pipes you want just 1 per pipe. Carrots need adequate space to develop, so thin them to the recommended distance (usually 15cm apart for this large variety).

How to Sow and Grow Giant Carrots

Growing carrot plants:


Keep the soil consistently moist but not waterlogged. Water deeply to encourage the carrots to grow longer roots. In the early stages be cautious not to dislodge the delicate seedlings during watering.


Carrots don’t require feedings at all as this can cause them to branch – they’re super happy with a hard life.

Mulching (Optional):

Mulching can help retain soil moisture and suppress weeds. Apply a layer of straw or compost around the carrot plants, being careful not to cover the seedlings.  If you’re a no dig gardener there’s no need to add extra organic matter.

Protecting from Pests:

Carrots are susceptible to pests like carrot fly. Consider using row covers or fleece to protect your crop. Companion planting with aromatic herbs like rosemary and sage can also deter pests.  You’ll be growing this variety in raised containers which will help prevent carrot fly.  Carrot flies can’t fly higher than 1 metre, so if you grow at height you can avoid the problem!


Carrots are usually ready for harvest 10-12 weeks after sowing, but this can vary depending on the variety. Gently loosen the soil around the carrots with a fork before pulling them out to avoid breakage. With giant carrots it is a good plan to grow more than you need to you can sporadically pull a test carrot to see if they have achieved the desired length yet.

Growing this giant carrot is so rewarding, particularly at harvest time when you unearth the fruits of your labour – such a wow moment.  Be sure to share your growing journey with us @shegrowsveg using #manpukujimonsters 

Happy growing!

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Video – How to Sow and Grow Carrots