17 May 2023 11:14

A melon plant portrait


Most experienced greenhouse owners have probably tried it at some point... Growing melons in the greenhouse. If you haven't tried it yet, this summer could be a great opportunity. However, I would say that it requires a greenhouse of at least 10 square meters as melon cultivation takes up a lot of space. Once you have tasted a homegrown melon, you will never forget it. The fruits are not quite as big as those you buy in the supermarket, but the taste is absolutely fantastic and intense - the taste of "Sun and Summer", if you ask me. 


The taste of melon 

The taste of the melon fruit is formed from many components, which can be divided into three main elements: the ratio of several types of acids, sugars, and flavours. 

The varieties of melon used for industrial production have two primary characteristics. The skin must be robust and hard. The flesh must be firm. This is because the fruits must withstand machine handling, transport, and long-term storage. The taste is therefor not the primary consideration. The varieties we grow in hobby greenhouses are not nearly as robust, the skin is often thinner, which makes the taste often much better. Varieties with a thinner and softer skin quickly release all flavour compounds when eaten. Therefore, a homegrown melon has a more intense taste. 


A big family 

Melon, Cucumis melo, belongs to the Cucurbitaceae family, also known as the squash family. Melon is related to many other well-known vegetables such as squash, cucumber, pumpkin, and watermelon. What they all have in common is their explosive growth and their great love for heat and direct sunlight. There are many varieties of melon (see overview from Only Foods). 

Melon is an annual plant with a creeping growth habit. That is, melon does not climb like the cucumbers do in the greenhouse. Melon prefers to grow in the bottom of the greenhouse and in the warmest and sunniest place in the greenhouse. Melon can also be grown upright, but it is not as easy as horizontal cultivation. 

The Origin of Melons

The exact origin of melons as a species is not known for certain. Some botanists believe that melons originated in India, while others think it came from Iran. Yet others believe its origins are to be found on the African continent. However, the common factor is a significant warmer climate than we know it from our gardens.

It is this warm origin that we need to mimic in our greenhouse when we want to succeed with growing melons. From seed to mature fruit, the process for melons is long, between 70 and 90 days. It is often this long development time that we find most difficult to replicate in the greenhouse. However, with a few tips and tricks, it can still be done. 


Growing Melons 

Melons are one of the last plants you should pre-germinate on your windowsill in April. A basic rule of thumb is to sow them 3 to 4 weeks before transplanting. Once the melon seed has sprouted, the plant develops quickly. Within weeks, the melon plants take up all the space on your windowsill. Therefore, you should start sowing now, so that the plant can naturally be moved outside when it gets too big. 

The temperature during sprouting should be around 20 to 25°C. The seeds should be covered with soil with a maximum of three times the thickness of the seed itself. That means the seed should only be covered with a few millimetres of soil. Always use seed and potting soil for indoor sowing. 

After sprouting, the plants need as much light as possible. Melon plants don't like temperatures below 15°C at any time, especially when they are small. If you want to be on the safe side, you should not transplant your melon plants until the temperatures in the greenhouse are above 15°C at all times. 


Planting in the greenhouse

You probably know that tomatoes can be planted deep in the soil without being damaged. With melons, it's the opposite. Melons are more sensitive to soil-borne fungal diseases. Melons should not be planted so deep that the new soil covers the stem and root collar (*) of the plant. It's important that you plant your melon plants in the warmest and sunniest places in the greenhouse. This is where the plant thrives the best.


Temperatures in the greenhouse

Although melons grow best at 28-35°C, the plant cannot tolerate temperatures above 40°C for very long. Most fruits are formed when the temperature is between 18.3-23.9°C during the day and not below 15.6°C at night. Fruits set best between 18.3-23.9°C. This is when the pollinating bees are most active.


Pollination of melons

With cucumbers, pollination challenges have long been outdated. It's a bit different with melons. Melon plants have both male, female, and hermaphrodite flowers on the same plant. The female flowers must be pollinated by pollen from the male flower before the melon fruit develops. You can tell if a female flower has been pollinated correctly when it forms a small knot in the flower base below the flower. You can play bee with a small brush and pollinate by hand, but our experience is that it's rarely necessary. Keep the windows open all summer. Attract pollinating bees into the greenhouse with flowers. You can for instance sow some honeywort, Phacelia tanacetifolia, or sweet pea, Lathyrus odoratus, and nature will do the rest.


How to get many fruits 

We all want as many fruits as possible on our melon plants, and here are a few tricks you should know. It's simply a matter of not being too good to the melon plants. You should not grow your melon in self-watering boxes for the simple reason that the plant has too easy access to nutrition and water. With a lot of nutrition and water, melon plants tend to produce a lot of leaves and fewer flowers. The plants will be in the so-called vegetative stage.

However, the goal is to get the plant into the so-called generative stage, where it sets flowers. In order to get it there, the plant should be stressed a little, for example, by letting the plant dry out between waterings. Another way to provoke the generative stage is to hold back on fertilization. 


Fun Facts 

  • Not all melons are sweet.
  • A melon fruit consists of 90% water, 9% sugar, and 1% protein. 


Bonus info 

  • Keep the base of the plant where the fruit develops dry - for example by letting the fruit grow on a plate. 
  • The fruit is ripe when it comes off the plant with a light pull. 


(*)The root collar is the place on a plant that forms the transition between the stem and the roots. The root collar is in a vulnerable position because the humidity constantly fluctuates around it, which makes fungal attacks possible.