Sprinkle several drops of water onto your edible leafy crops. Take a close look at how the water behaves once it hits the plant's leaves. Some may form droplets and roll down easily but some may stay on the leaves without a shape. You may also notice that, for certain kinds of greens like choy sum and cabbages, the leaves can be quite glossy, while others like kale may look glaucous. That’s because these leaves are covered by a layer of naturally formed wax, a.k.a, epicuticular wax/ a mix of lipids. Depending on the thickness, structure, and composition of the wax, leaves may feel and look very different.
Wax serves important purposes for greens. By coating on leaves, wax conserves water stored in the plants. Leafy greens, as the name implies, have mostly leaves as their structure and every leaf is a large surface for water evaporation. This could be a huge stress for the plant. That’s why they produce wax on the leaves naturally to limit water loss. This wax also protects the greens as a physical barrier from pests and diseases.
Planting choy sum in spring is a big challenge for local farmers, but Cheong Gor from Hong Miu manages to produce a small amount of choy sum with some glow on leaves.
Wax is good, but it is also energy-demanding for a plant to produce. There are so many things happening in a plant that needs energy to drive. For instance, a plant needs to make new cells to grow, and new cells require components like proteins, cellulose, and chlorophyll to build, each requires energy to make. Only when a plant is healthy enough to be highly efficient in photosynthesis, then it can allocate enough energy to make wax sufficiently that coats its leaves and help them become water-proof.
Next time when you have leafy greens, try to see how the leaves behave with a splash of water. The better and healthier the greens are, the quicker these water droplets will roll off of the leaves!
The waxy cuticle is on the surface of leaves. It is a very thin layer but performs a key role in plant health.
Chinese cabbages in Hong Miu Farm had severe pest problems last year.
This year, the Chinese cabbages are not free of pests, but have shown huge improvements. We look forward to continuing the monitoring process on how compost application and nutrient amendments at Hong Miu farm will help to produce thicker and more glossy leaves in the next crop season!
Although leafy greens don’t look oily, they do produce lipids. Leaf wax is a clear example, but actually, plants need lipids in every part of their structure - from seed to root.
References:
Allen, D. K., Bates, P. D., & Tjellström, H. (2015). Tracking the metabolic pulse of plant lipid production with isotopic labeling and flux analyses: Past, present and future. Progress in Lipid Research, 58, 97–120. https://doi-org.proxy.library.nyu.edu/10.1016/j.plipres.2015.02.002
nagwa (n.d.) Lesson Explainer: Support in Plants. nagwa. Retrieved from: https://www.nagwa.com/en/explainers/573184167273/