Unravelling the mystery of drooping leaves
April 12, 2021 By Gagandeep Singh Bhatoa and Mohyuddin Mirza
Many growers use the term “praying” leaves as the normal leaves. These are leaves that are upright and expanded to trap light as much as possible. Among cannabis growers, praying leaves are considered a sign of healthy, functioning leaves.
How to recognize drooping and wilting in cannabis plants
Water is one of the most important aspects of keeping cannabis plants healthy and robust. Watering cannabis isn’t always as simple as it may appear. Overwatering and underwatering are common issues a grower faces. It’s imperative that growers do not confuse cannabis “drooping” leaves with “wilted” leaves, as they have completely opposite causes.
Drooping leaves are often a result of overwatering. Too much watering drowns the plant’s roots and causes abscisic acid to build up. Leaf stomata starts to close up and creates obstruction in photosynthesis and respiration. Both the loss of oxygen and the build up of abscisic acid will severely weaken the stem and leaves of the plant above the surface.
On the other hand, underwatering can lead to extremely dry conditions that will leave cannabis plants thirsty, eventually causing them to wilt. Underwatered plants will look ill and weak, with dry and droopy leaves, and the tip turning yellow and curl down.
From drooping leaves back to praying leaves
The picture above shows a plant where most of the leaves are in “praying” mode. There are many contributing factors, including turgor pressure, lighting and nutrients, that play important roles when it comes to optimal growth of crop.
Potassium has a role to play in maintaining turgidity of stomatal guard cells. Turgor is the pressure exerted by water inside the cell of the plant. A sufficient level of turgor pressure should be maintained so that the plant keeps growing. Without sufficient turgor pressure within plant cells, plants will wilt.
Turgor pressure helps keep a plant standing upright with its leaves outstretched or tipped up to absorb as much light as possible. When turgor pressure is high, this allows maximum expansion of cannabis leaves to receive adequate or more sunlight.
Yellow leaves often result from nutritional deficiencies. But if you know the nutrient situation is optimum and observe the praying leaves go from green to yellow, it could be triggered by light stress. In that case, you may move the lights further away or rotate your plants around to allow the stressed leaves to get more shade.
It’s common among growers to think that plant is stressed from a deficiency when the issue is actually light stress. In that case, the praying leaves are a sign to help you narrow down the cause to your light levels. So, it’s important to give plants as much light as possible without triggering light stress. Providing a sweet spot where the plant can get high light levels which result in healthy green leaves pointed up are good indication of a fast-growing, healthy cannabis plant.
Finding your plants’ sweet spot
In general, good watering practices should be followed and “good” depends on the grower’s experience, type of growing medium, water quality and climate control parameters.
Some growers have a tendency to use light period temperature of over 26 C, which require more frequent watering to meet the transpiration demand of the plant. Many growers who use hydroponic methods, especially recirculating water and fogging, should pay more attention to root health conditions and dissolved oxygen.
To fix the wilted or underwatered cannabis plants, always test the growing medium for moisture content, by pressing your finger about an inch down into the medium. You can also determine saturated weight of plants in a container and a wilting point weight, and thus use the scale to properly water the plants.
It’s important to make sure that plant roots have access to moisture at all times. Plants are constantly losing water through their leaves via transpiration and this is actually how plants get water up from the roots. As the plants lose water from the leaves, it pulls water up from the growing medium like a straw. When there’s not enough water at the roots, many plant processes cease to function. If roots actually dry out, the shoots will also suffer and could die off. Often the grower is able to see how dry the growing medium is.
A big indication that the plant is being underwatered is when you can see the growing medium separating from the container. You can see the starter cube separating from the soil because it’s so dry. The leaves will become very dark green/blue, smaller in size and thick. Most of the time the Electrical Conductivity will rise in the growing medium because of underwatering. In such situations, rehydrate the growing medium with pH adjusted water only before resuming nutrients dosing.
(For a list of references cited in this article, please email the editor at firstname.lastname@example.org)
Gagandeep Singh Bhatoa is a Plant Health care specialist in Lethbridge, Ont.
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