Kaffir Lime Care – Yellow Leaves Problem
by Kasma Loha-unchit
17. "Why Are the Leaves on My Plant Turning Yellow and Dropping?"
If the yellowing is happening to new leaves at the tips of the branches, it likely means that your plant is not getting enough nitrogen, so you'd need to feed it with a high nitrogen fertilizer (the first number in a 3-number sequence on the fertilizer label). Sometimes it can also reflect a calcium deficiency. If your plant is already being fed regularly with a high nitrogen fertilizer that also contains a wide range of micronutrients, it could mean that the plant may be suffering from either drought stress or the stress of over-watering. Either extreme can upset a plant's photosynthesis since its roots might not be able to absorb the nutrients you feed it. Basically you'd need to bring it out of stress and into balance.
There're a number of products I know which are useful in helping restore vigor to plants when they are in stress. One is an organic foliar plant food called Wonder Grow, with nutrients derived from Norwegian seaweed and yucca extract. Another is "SUPERthrive!", a supplement that contains 50 vitamins and hormones formulated to help plants flourish and survive conditions of over- as well as under-watering. Both will make the roots of your tree grow stronger and better able to survive both drought and damp conditions and to absorb nutrients in the soil.
In addition, products that contain live spores of the beneficial mycorrhizae fungus which stimulates root growth can help revitalize trees beset by root problems. Incidentally the citrus fertilizer made by E. B. Stone Organics mentioned in the foregoing section does contain mycorrhizae spores to promote strong, healthy roots. Another useful product is Dyna-Gro's "Pro-Tekt" which contains potassium and silicon to reduce stress caused by heat, cold, drought, insects and diseases. It improves heat and drought tolerance, increases resistance to environmental stress and enhances growth for healthier, stronger and hardier plants. I've used the latter with great success in helping my redbud tree recover from serious fungal disease that nearly killed it a few years ago. I now use it occasionally on plants that are susceptible to root rot as a preventative measure. Actually any of the foregoing products can be used regularly as a nutritional supplement to prevent problems before they arise.
If the yellowing of leaves is happening in between veins of older leaves on the lower part of the branches, it most likely means that your plant is experiencing an iron deficiency. You can buy a chelated iron supplement for citrus at the nursery to take care of the problem. Sometimes this symptom can also come about from a deficiency in other trace minerals the tree requires, such as magnesium, manganese or molybdenum. You might want to give your tree a supplemental feeding with a fertilizer that contains a wide range of micronutrients, such as a seaweed based fertilizer (seaweed contains over fifty natural, vital trace elements, minerals, vitamins and other nutrients essential for growing healthy plants). Other symptoms of nutrient deficiencies include: brown spots on leaves (copper or molybdenum deficiency), leaves spotted and curled and leaf tips and edges turning yellow (potassium deficiency), and pale green or yellowish young leaves (sulfur deficiency). A tree that is generally healthy with plenty of new leaves but the leaves are smaller than normal may need more nitrogen and/or more water.
If both new and old leaves are yellowing and dropping off at a disturbing rate and there hasn't been an extreme heat wave or a freezing cold snap, you may have a serious problem. Your tree may be suffering from some kind of root problem, or it simply can be a sign of nutrient deficiencies in several of the major and secondary nutrients the tree needs to flourish. You might wish to consult a plant doctor (i.e., horticulturist or arborist) at a reputable garden center for his/her opinion and advice.
The major yellowing could be the symptom of fungal root disease brought about either by poor soil drainage or from excessive watering. It's also likely that your tree absolutely can't take the hot, dry heat where you've put it, or is terribly stressed by a recent prolonged heat wave that could have subjected it to alternating periods of dried-up and waterlogged soil. If it's grown in the ground, you might want to give it a solution of Dyna-Gro's Pro-Tekt, which is what I did with my redbud tree when it lost nearly all its leaves in mid-summer one year. Then monitor your watering so you don't give the plant any more water than it needs. Withhold feeding your stressed plant the usual fertilizer until it shows signs of recovery. This helps re-direct the plant's energies into healing.
If the tree is grown in a container, you could take the plant out of the pot, check the roots and the wetness of the soil. If the roots occupy just a small portion of the pot and the soil beneath is soaking wet, then root rot from excessive watering is indeed the problem. Gently remove as much soil around the rootball as possible without causing further injury, prune off the ends of roots that look rotted with sharp shears, and repot the plant in new soil mix into a smaller pot just large enough to accommodate the rootball. Water in with a dilute mixture of Pro-Tekt or SUPERthrive! and withhold feeding the plant until it recovers. Prune the tree back hard immediately after repotting so that it is proportional to the size of the remaining rootball. Keep your fingers crossed and hope for the best!
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