Melons in a greenhouse – the basic facts

Looking at the global hydroponics produce trends, cultivation of melons in soilless culture is a fairly new trend that is showing promising results in many parts of the world. Though you might think that the size of melons would make them hard to grow hydroponically, they grow quite well in coir substrate in greenhouses and poly houses.

Melons have to be trellised well and supported to optimise quality and appearance.

Most of the melon growers focus on growing two high quality melons per plant. Melons in hot conditions can be grown up to 4 cycles per year, as it takes around 80 days from planting to harvest. Melons are a crop that requires a very low moisture level in the final phase, just before harvest. It’s correct for all types of conditions but even more critical in tropical weather. The growers that grow melon in grow bags experience better root system, zero root diseases, less physiological disorders, more homogeneous fruit size and darker flesh colour. The biggest concern with growing melons hydroponically is making sure that they have a controllable growing medium, adequate light and good trellising support for their increasing weight. With the proper irrigation, lighting and maintenance of the nutrient solution levels, it helps to maximize melon production in a short period of time. Production of melon in soil versus in a grow medium, has shown a yield of 9.2 Kg/Sq m compared to in-soil production of 4 Kg/Sq m with the same melon variety. Melon seedlings should be provided by your seedling grower. This gives you as producer the peace of mind that your success in growing melons – especially as a new grower – started on the right foot. With the correct grow mix, growers succeed to grow two or three melons per plant (comparing to soil) with excellent brix levels of 15 and higher. Ideal greenhouse temperatures are between 18°C and 23°C. They should be regularly ventilated to keep air fresh and disease free. For the best yields, average root temperatures for your melons should be kept around 21°C or higher, so it helps to put the grow bags into the greenhouse well ahead of planting time, in order to heat up prior to receiving the seedlings. The pH of the grow mixture should be from 6.0 to 6.5 and contain rich organic matter. Compost or manure is best for this. Frost is an ever-present danger to production of melon, especially at either extreme of the growing season. Melons outdoors are a high-risk proposition, but they are ideal for greenhouse conditions. The melon vines will need some support once they get a bit bigger. Prepare for this early by installing trellising wires for

them to climb and cling to, and rope with anchor stuck into the grow mix, a few centimetres from the root ball. Tie the strongest shoot to the support once it is long enough. Pinch the side shoots to remove them and the plant will grow upwards – this is to train the plant in the right fashion. Once the main stem reaches the full height you want it to grow, pinch off the end of it to trigger melon production. Limit the number of melons per vine to two or three. This will result in bigger melons, rather than a larger number of stunted, small ones. Irrigating your melon plants is also a big factor. Water should penetrate into the deep roots, but without saturating or swamping them. Too much water will have the melons split open. Aim for a grow medium that is moist, but not wet. A drip or similar watering system is ideal but must be regulated to not overwater. Liquid tomato fertiliser, applied once per week once fruit has started to appear, will keep your melon plant fed and happy. Remember to scale down on irrigation once fruit are at the right size. In order to get those fruits in the first place, the flowers must be pollenated. Open doors will allow bees to enter and do this job for you, or you can do so yourself. With a small, soft brush, go from flower to flower, brushing the delicate internal structures of the flowers, one after the other, until you have made the rounds to each of them at least once. A few days later, the female flowers will have tiny fruits beginning to form on them. The ones that don’t are likely male flowers, and these should be removed. The growing melons will require regular inspection for support on the trellising system. There are small net ‘hammocks’ available but care must be taken when fitting these to support the melons and not to disturb it calyxes. Removing any leaves that block the light from the fruit is important too. Light on the fruit will result in a sweeter melon that ripens sooner. During the melon growing stages, above average rising temperatures can be an issue. To prevent damage on very hot days, increase humidity in the greenhouse to lower the temperature. A mist watering system is recommended. Melons ripen in about three weeks’ time. The producer can therefore structure his growing and marketing to suit him best. When seedlings of same age were planted, raised under the same circumstances, treated with water and fertilizer equally, it should offer a very simultaneous harvest. To tell when a melon is ready for harvesting, watch for the time when a melon stops getting bigger. If you tap it, it should sound a dull thud. Beginners might want to open one to test its progress and then compare it to the state of others around it. If you wait too long, and the vine separates from the melon, this is a sign that it is too late – the melon will be rotten inside. The serious melon producer will soon learn the little intricacies of production management on melons. It is a popular fruit and always in demand on the market. Melon production is a financially viable proposition for a greenhouse farmer with his finger on the pulse of his business. JS (pictures: Riococo)

Trellised melon plants in a greenhouse. Note the beehives.

Worldwide Expertise for Food & Flowers

Specialists in Horticulture

More information? Herbert Stolker Consultant KZN, Gauteng, Mpumalanga and Limpopo T +27 (0) 72 545 5757 E h.stolker@delphy.nl www.delphy.nl

Yulandi Holtzhausen Consultant Cape Town region T +27 (0) 82 896 2156 E y.holtzhausen@delphy.nl