Question

What is the ideal nutrient ppm concentration for watermelons, and what special care is needed to grow square watermelons?

Answer
By Lynette Morgan | Last updated: January 9, 2017

Watermelons grow extremely well in hydroponic systems. Provided conditions are warm enough, plants will produce large, sweet fruit. The elemental levels for growing watermelons, as with most fruiting crops, changes as they go through the vegetative and into the fruiting stages of production. Below are some nutrient recommendations for each stage of growth in ppm:

Watermelon ppm values for hydroponic production:

Vegetative (EC = 2.0–2.4 during this phase): N=243 ppm, P=67 ppm, K=208 ppm, Mg=85 ppm, Ca=258 ppm, S=113 ppm, Fe=5 ppm, Mn=2.5 ppm, Zn=0.25 ppm, B=0.70 ppm, Cu=0.07 ppm, Mo=0.05 ppm

Fruiting (EC = 2.0–2.2 during this phase): N=202 ppm, P=91 ppm, K=322 ppm, Mg=101 ppm, Ca=169 ppm, S=134 ppm, Fe=5 ppm, Mn=2.5 ppm, Zn=0.25 ppm, B=0.70 ppm, Cu=0.07 ppm, Mo=0.05ppm

Growing square watermelons involves placing the young fruitlet inside a square box or mold while it is still attached to the vine. As the fruit grows and fills the mold, it takes on the shape of the cube. Japanese melon growers also produce heart-shaped melons using a different type of fruit mold. The main points to consider are the size of the square enclosure—it needs to be just slightly smaller than the mature size of the melon—and growers need to be continually checking the watermelon towards the end of growth so that it can be harvested before cracks or splits start to occur. In Japan, the square watermelons grown in this way are typically not edible, they are ornamental fruits only for display, as the melon has to be harvested before it is fully mature. Japanese growers traditionally used tempered glass cubes for these melons, although nowadays commercial melon molds can be purchased that are made from acrylic or clear polycarbonate that bolts together in the middle, making removal at harvest much easier. The square molds are usually transparent, as this allows the growers to check that the melon is in the correct position and it also promotes better coloration. Square molds for melons also need some drainage holes/ventilation to help prevent moisture buildup inside the cube and the fruit rot that this would promote. Good luck with your watermelon experiment.

Share this Q&A

  • Facebook
  • LinkedIn
  • Twitter

Tags

Hydroponics Ventilation Plant Nutrition Tools and Equipment Plant Growth Harvest Growing Methods Metering & Monitoring

Written by Lynette Morgan | Author, Partner at SUNTEC International Hydroponic Consultants

Profile Picture of Lynette Morgan

Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.

More Q&As from our experts

Related Articles

Go back to top
Maximum Yield Logo

You must be 19 years of age or older to enter this site.

Please confirm your date of birth:

This feature requires cookies to be enabled