How do I get thick stems on cilantro plants in hydroponics growing? I am getting a vice-like tangled mess.

Young cilantro plants tend to naturally have quite thin stems, so obtaining a really thick stem is probably not likely. However, there are a few factors that can help make the plants as sturdy as possible.

The first is overcrowding — cilantro seed is often over sown in clumps of many seeds and the resulting high number of seedlings tends to result in thin, stretched plants that tangle up together. A better option is to sow seed singly, separated from each other by at least one inch initially; this will give sufficient room and light for the seedlings to develop. Plants can then be further spaced out as they develop so that they are not touching each other. If seedlings or plants are too close together and overcrowded, they compete for light by elongating upwards with thin, weak stems.

The other factor is light — cilantro is a high light, warm season herb and will perform best under a good intensity of full spectrum light for the most compact plants. This is particularly essential during the early, post germination phase when cilantro plants can rapidly elongate upwards. If growing under artificial light, increasing the blue spectrum and overall PPFD can help with more compact plants and thicker stems. If growing outdoors or in a greenhouse, exposure to full sunlight as soon as the seedling has the first true leaves expanded is recommended. Cilantro seedlings and plants grown under low winter light with shorter day length then to be taller and thinner than those grown with higher light levels. Also, a combination of warm temperatures (higher than 22°C/72°F) and low light will cause the most significant stretching and resulting thin stems of young cilantro plants, while overall high temperatures over 28°C/82°F often lead to very tall, thin plants.

Nutrition can also play a role. Higher EC helps maintain strong and compact plants and cilantro seedlings should be given a half-strength, fully balanced nutrient solution as soon as the first leaves have expanded, increasing this to a full-strength solution (ED 2.0 – 2.2) once plants are two weeks old.

Choice of cilantro variety can also help significantly with growing full, bulky plants with sturdy stems. Some of the more modern cultivars have been selected for these traits and one of the best ones would be the cilantro cultivar Cruiser. This variety is used under commercial production for its large leaves and thicker stems and performs very well in hydroponic systems.

Good luck with your cilantro plants!

Lynette Morgan
Suntec International Hydroponic Consultants