Before growing watermelons the grower should consider the following:
He/she should be aware that the plants will need quite a bit of growing space, and that they require long hot summers where day temperature gets to 27°C (80°F) and the night time temperatures doesn’t go below 13°C (55°F)
This raises the question; do you have sufficient space?
This is particularly relevant if you also intend growing plants such as tomatoes, cucumbers and peppers in the same greenhouse/tunnel.
One could consider using a covered coldframe, and growing through black PVC sheeting, this will help to raise the soil temperature.
What variety to grow?
If your choice is a seedless variety, you will also need to plant a seeded variety of watermelon nearby.
Seedless watermelons will not produce fruit without a seeded variety planted nearby for pollination.
Week 16: Sow seed singly (on edge) into 75mm (3") pots of seed compost.
Germinate at 18°C (65°F)
Germination will take five to seven days.
After germination place the seedlings where they can get maximum light (but not direct sunlight) maintain a temperature of 10°C (50°F)
Week 17: When the seedlings have three true leaves, pot them singly into 150mm (6") pots of potting compost, setting them so as the bottom set of leaves are just above soil level.
Week 20: Prepare the growing bed by incorporating liberal amounts of well rotted manure or compost.
Rake in bone meal mixed with lime at a rate equivalent to 100gms per sq.metre (4oz/sq. m)
Week 22: Plant out in the greenhouse border 900mm (3ft) apart.
Water the plants in to settle the soil around the root ball, then water regularly for the rest of the growing season.
To prevent mildew, avoid wetting the leaves when watering.
Week 24: Pinch out the growing tip of the main stem when it is 600-900mm (2-3ft) long.
Week 26: Feed fortnightly from now on, with a high Nitrogen fertiliser.
Assist pollination by removing the male flowers and brushing them into the centre of the female flower, which is recognizable by the embryo fruit behind the petals.
Allow no more than three fruits per plant.
Ideally pollinate all three flowers at the same time then remove all other flowers.
Harvest when the tendrils on the stems become brown.
The surface of the melon should be dull, hard and rough, and the area of the watermelon that is in contact with the soil may turn slightly yellow.