Since 2020 I have been growing melons in a small but professional style. At the beginning I had a few questions about cultivation that I couldn’t find an answer to at first, especially not within Switzerland. Over time, I was able to try out many different farming methods and found helpful non-fiction literature from abroad. In this short journal I would like to address some of the points that I have learned so far in the cultivation of sugar melons and watermelons.
When growing melons in Switzerland (cold conditions) it became clear that they have around three harvest peaks. The reason for this is found in the structure of a melon plant. Like all cucurbits, melons are climbing plants and prefer to grow up a climbing aid. This has several advantages for the plant. On the one hand, this leads to better utilization of light, on the other hand, the leaves dry faster and fungal diseases have a harder time spreading. Modern varieties of pumpkins, but also melons, have produced much larger fruits than originally intended by the plants itself. If such varieties were grown vertically, the fruits would eventually break off as they become too heavy. This is why most pumpkin plants are grown on the ground today, even though the plants are always looking for a way to the sky. However, if melons are grown on the ground, this quickly results in a messy jungle. If, on the other hand, the plant grows vertically on a climbing aid, it is much easier to get an overview. This is why the following drawings are also intended for this purpose.
Vertical cultivation is very easy to achieve in a greenhouse and is preferred anyway, as more plants can be grown in this way. The picture above shows a plant that is about 3 months old and growing vertically (climbing support is missing for a simple schematic representation). The plant already has several larger fruits. This cultivation method clearly shows that the fruits hang at different heights, usually on so-called side shoots. The fruits ripen from the bottom to the top of the plant, as the oldest fruits always hang at the bottom. This “tiered harvest” usually takes place on three side shoots per plant, which explains the average three harvest peaks per year.
How is a melon plant structured and how do you have to prune?
But what is a side shoot and how does the plant actually grow? These questions are important to understand when growing melons. All melon plants have a so-called main shoot (see picture below, horizontal view of the plant from above without side shoots).
As with all cucurbits, only male flowers usually bloom on the main shoot, but it cannot be ruled out that a female flower may also appear. After successful fertilization of the female flowers, the melon fruit finally forms. Male flowers (bottom left) are very easy to distinguish from female flowers (bottom right) in cucurbits. The latter have a short flower stalk and do not have the typical ovary, a roundish thickening behind the petals.
The side shoots always grow away from the main shoot at the leaf axils and bear the female flowers in plants of the pumpkin family. All side shoots from our example plant are shown in color below, the main shoot is gray.
The side shoots are often counted from bottom to top in order to name them and determine the development status of the plant. The oldest side shoot, and therefore the lowest, is the 1st generation side shoot. Our example plant therefore has several side shoots of different ages, whereby the youngest side shoot is from the 3rd generation. This true representation also clearly shows that the side shoots never stop growing during the vegetation period and become longer and longer. The side shoot of the 1st generation is therefore much longer than the side shoot of the 3rd generation and does not stop growing after the formation of the first fruit.
At first glance, this seems very tempting, as more and more fruits are formed per side shoot. However, allowing all side shoots to grow as long as possible in order to achieve the maximum number of fruits is not a good strategy. I also did this in my first year and later bitterly regretted it. In the beginning I sometimes had over 20 fruits per plant, but in the end I harvested far fewer, and their taste was never comparable to the fruits I produce today. The reason for this is simple: the more fruit a plant bears, the more “offspring” it has to provide for, which can very quickly lead to the plant becoming malnourished. This can have significant negative effects on fruit quality and plant health. For this reason, even professional growers recommend leaving only one fruit per side shoot. The side shoot is cut off after about one or two leaves after the fruit.
But caution is advised! Watermelons, on the other hand, tolerate pruning of the side shoots very poorly and should therefore not be pruned, nor do their side shoots grow as crowded as those of sugar melons. If you have the space, you can grow watermelons horizontally on the ground, as most varieties are not suitable for vertical cultivation because the fruit is too heavy. Small-fruited watermelons as well as large-fruited sugar melons (> 1 kg) can still be grown vertically, but the fruit must be supported separately at a later stage.
As is so often the case, there are exceptions when it comes to cutting sugar melons. Unfortunately, this information is very difficult to access and often only available to growers and large-scale producers. Among other things, I found that melon plants with smaller fruits have a lower yield after the side shoots have been cut, compared to untrimmed plants. Modern varieties such as “Honey Rock” from the USA should therefore not be pruned at all. The smaller fruits usually ripen all together and it is not necessary to control the fruit yield for fruit quality, provided the growing season is long enough. In conversation with an American farmer, I found out that in America the main shoot of this variety is sometimes topped after the second side shoot. After topping, the two side shoots are allowed to grow unhindered. This is said to result in many more fruits per plant. I have not yet tried this method myself. European cultivars of the Charantais type are more susceptible in this respect and should usually be pruned as described above. In general, the rule of thumb that has worked well for me is that sugar melons with fruit weighing more than one kilogram should always be pruned on the side shoots. For smaller fruits, this is not absolutely necessary for the fruit quality, but it does bring many advantages during the harvest.
Another care measure during the cultivation of sugar melons is the cutting of the first side shoots. This is sometimes done to support the plant in its vegetative growth for the first time. In this way, the plant does not go straight into fruiting and first gathers some strength for the growing season. In my opinion, this measure is of great importance if the plants cannot be optimally fertilized during the growth phase. In my cultivation, I have not noticed any difference in fruit quality or yield, but I have noticed a difference in the start of the harvest. Logically, plants that are prevented from forming fruit for the first time bear fruit that is ready to harvest much later. For me, this is an important criterion for not pruning the plants at the beginning. However, if you are not dependent on an early harvest and have long, warm fall days in your region, you can make good use of this cultivation measure for a strong plant.
I hope that this short article will provide many hobby gardeners with an understandable overview of how to prune sugar melons for optimum yield and fruit quality. With this in mind, have fun caring for your plants! If you are unsure whether you should prune or not, please contact me and give me the exact names of your melon plants. I will try to find out their ancestry so that I can give you more detailed information.