Watermelon Growing Guide

5 Steps to Watermelon Planting Success

  • Choose a hot, sunny spot in well drained soil. Summer is the best time to plant watermelons in New Zealand. 
  • Prepare your soil with organic matter like compost and sheep pellets.
  • Add a layer of citrus & fruit mix to plant into. 
  • Feed your watermelons regularly with seaweed tonic until they reach full size.
  • Give watermelons plenty of water in early stages of growth. 

Follow our full guide below to a bumper crop of homegrown watermelons.

Watermelons are a summer favourite! Vast and sprawling, they are grown the same way as their vege relatives from the curubit family - pumpkin, squash and cucumber, but the flesh is much sweeter. With their delicious red flesh and glossy green rind, watermelons are a refreshing summer snack and can range in weight from 2-3kg up to a gigantic 20kg.

Prepare

If you’re sowing seeds, watermelon seeds can be sown monthly from spring to early summer. Sow your seeds in Tui Seed Raising Mix indoors as they will have more chance of germination. If temperatures are below 15°C, they may not germinate properly.

Seedlings can be planted into their permanent spot in the garden when they have about five leaves.

Watermelons will thrive in regions with hot summers, as they need a long period of warmth to grow and reach full maturity.

Plant

Like building a house a good foundation is the key to success in your garden. The better the soil, the better your plants will grow. Watermelons prefer sandy, well-drained soil.

If you are starting with an existing garden bed dig in organic matter like Tui Sheep Pellets and Tui Compost to your soil. Then you can add a layer of Tui Citrus & Fruit Mix.

The best times to plant are early in the morning or late in the day, so the plants aren’t exposed to the hot sun straight away. 

Planting watermelons in garden beds

Position your watermelons in the sunniest spot in your garden, sheltered from winds and salty air. Protect your watermelons with frost cloth if frosts are a risk.

Watermelons have sprawling lateral growth, so they need a lot of room to grow. Plant melons on low mounds 1.5-1.8 meters apart, or up to 3 meters for larger watermelons. Grow two plants on each mound and trail the developing seedlings in opposite directions from one another.

Watermelons plants can be encouraged to grow up frames to reduce damage to the fruit. Either insert canes and wires or plant them near a sturdy fence.

  • Soak seedlings in a bucket of Tui Organic Seaweed Plant Tonic and allow to drain. This will help prevent transplant shock and give your plant a healthy boost.
  • Add a layer of Tui Citrus & Fruit Mix to the planting area.
  • Dig a hole, approximately twice the depth and width of the root ball of your plant.
  • Gently loosen the root ball of your plant and position the plant in the centre of the hole.
  • Fill in with Tui Citrus & Fruit Mix.
  • Press soil gently around the base of the plant.
  • Water your plant well and continue to water regularly.

Planting watermelons in pots and containers

Watermelons can also be grown in shallow but wide containers, although you can expect a smaller crop. Leave plenty of room around the container for lateral growth.

  • Soak seedlings in a bucket of Tui Organic Seaweed Plant Tonic and allow to drain. This will help prevent transplant shock and give your plant a healthy boost.
  • Partly fill your container with Tui Citrus & Fruit Mix.
  • Gently loosen the root ball of your plant and position the plant in the centre of the container.
  • Fill your container with Tui Citrus & Fruit Mix up to 3cm from the top.
  • Tap the container gently on the ground to settle the mix.
  • Press soil gently around the base of the plant.
  • Water your plant well and continue to water regularly.

Nourish

Feed your plants and they will feed you. Watermelons use nutrients from the soil as they grow, so replenishing the nutrients ensures they will grow to their full potential.

Feed regularly with a liquid fertiliser such as Tui Seaweed & Fish Fertiliser or Tui NovaTec Premium fertiliser - which feeds plants for up to four months. 

While your watermelons are growing, pinch out the growing tips when they reach 1 metre. This will encourage more side shoots to grow. The side shoots produce female flowers which means more potential fruit.

Pollination

Bees and other inspects pollinate melons, but hand pollination might be required, especially if there are not many insects around. The male flowers generally occur in small groups, while the females are solitary. The females are also recognisable by a swelling behind the petals. Pollinate several female flowers at the same time, they will then all set fruit and develop at the same pace.

Watering

Watermelons need plenty of water and a humid environment in the early stages of growth. Be careful to not let water collect around the stems, as they will rot quickly.

For container grown watermelon, incorporate plenty of SaturAid into the soil to ensure thorough and even water retention.

Well watered, well nourished watermelons will have a better chance of keeping insect pests and diseases at bay.

Harvesting

Watermelons are a summer fruit, and can mature into mid-summer, depending on when seeds were planted. Watermelons should be left to mature on the plant. You can tell when watermelons are ready to be harvested when the fruit gives a dull, slight echo when tapped.

tui tips

  • The more sun your watermelons get, the sweeter they’ll be.
  • Heavy melons need to be protected with netting, or place straw underneath each fruit to keep it off the ground.
When should I plant
in
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Harvest in 140-160 days