When a plant needs something it is lacking, it will often provide signs in the foliage. Understanding these signs will help the gardener solve garden problems more effectively. The following are a few signs to look for:
1- droopy leaves, wilting- this is an indication that the plant needs water. Check the soil below the surface. The deeper you check, the better you can gage the quality of the soil. If the soil is dry, water deeply. Sometimes, the leaves might act droopy even though the soil is wet. If too much water is the problem, after some time, the droopy leaves will turn dark colors and die. If an excess of water is the problem, dry the soil out by not watering it. Repot the plant if necessary.
-it should also be noted that sometimes, during the peak afternoon heat of the summer, many plants will droop their leaves to avoid sun scald and conserve water. A general rule of thumb is that if the leaves are perky in the morning, they don’t need water, but if they droop in the morning, this is sign that they are thirsty.
2- discolored leaves- depending on the color, this could mean many things.
If the leaves are the color:
-Brown- pick a leaf off the stem and bend it between your fingers. If it is crunchy and crumbles, the leaf is too dry, and so is the plant. If the leaf bends and flexes between your fingers but doesn’t crumble, then this is a sign that the plant has too much water, and the roots are beginning to drown. Always check the soil after the leaf crumble test to confirm conclusion.
-Yellow- this could mean a few different things. Often, this means that the plant needs to be fertilized, and the remedy is nitrogen, and micronutrients like iron, calcium, and magnesium. If the plant continues to shed yellow leaves through the seasons, year after year, and starts to look sickly, this could mean that a pH imbalance in the soil is responsible. This could mean that your soil is either too acidic, or too basic (or alkaline, the most common problem in Texas), and important nutrients for the plant are being locked away in the dirt. If your soil is too alkaline, then amend the soil around the plant heavily with compost, pine bark mulch, and/or coco-fiber. Spray liquid seaweed often, and/or spread epsom salts or horticultural sulphur in the cool months. If you soil is too acidic, add lime, ashes, or other basic soil amendments. These steps should help correct the problematic yellow of the leaves.
-yellow could also be an indication of a fungal infection. To check for this, examine the leaf for circular raised bumps. They might appear to have tiny bubbles on top. This is a good indication that a fungus is at work causing the leaf to die. See “Gardening 101” to resolve basic fungal problems.
– white- if the leaves have a coating of white on them, examine it closely with your thumb. If it is a powdery substance, the plant has powdery mildew, and any organic fungicide will do. (see “Gardening 101“) If, on the other hand, the white seems to be an infestation of insects (there are many kinds, like scale and whitefly), then cut the bad stems off the plants and spray with an organic insecticide (more on this later).
-purple- the leaves of many plants will turn purple in the fall, and this is normal. Most of the time, these leaves will fall off for the deciduous plants, while other more “evergreen” varieties will keep their purple leaves all winter. The purple is the result of a shift in the production of certain chemicals at the onset of colder weather and diminishing periods of sunlight. However, if during the peak of the growing season, and a plant’s leaves turn uncharacteristically purple, this could be an indication of some kind of cultivation stress.
-unnaturally multi-colored , “sickly”- this could be an indication of a kind of cultivation stress, like drought, or a problem with fertilizer concentration. More importantly, it could be an indication that the plant has contracted a virus. If this is the case, look for unusual sap or “weeping”, look for leaf “burn”. If you are unsure, call a specialist to very this. If it is a virus, then parts of the plant will die off, eventually taking the whole plant with it. It is best to remove an infected specimen, throw it away, and heavily compost the soil is was growing in. It would be best to not plant the same kind of plant as the infected one in the same spot.
3- If the leaves appear burned on the edges- this could mean heat or drought stress. The solution is to water the plant deeply, and it will usually recover. If the leaf burn occurred after fertilization, then this is probably a nitrogen burn. Hopefully, the plant can be saved by deeply watering the soil to dilute the nitrogen before it burns the entire plant. Sometimes, a leaf burn is the result of a viral infection. If this is the case, look for excess sap, “weeping”, discolored leaves, and dead stems. Consult a specialist if you are unsure.
4- unnatural spots on the leaves- this could be a fungal leaf spot. Look for raised bumps like bubbles on the surface of the spot (a magnifying glass comes in handy). Treat this with an organic fungicide, and try to correct any cultivation issues that might lead to fungal leaf spot. (see “Gardening 101“)
5- holes in the leaf- insect and predator damage. Small, tiny holes or spots can be aphids, or “rasping” insect damage. Big chunks of leaf cut from the edges is typical of grasshopper damage. Smaller caterpillars will eat away at the interior parts of the leaf, while snails, slugs, and large caterpillars can eat entire leaves in a brief amount of time. A general natural or organic insecticide/ repellant will help take care of this, such as neem oil, spinosad, cedar oil, garlic, or pyrethrum. For caterpillars use spinosad or BT. Grasshoppers are are difficult to treat for. For such things, sometimes it is best to think outside of the box and hang a bird feeder in the area, and let the birds take care of the grasshoppers.
6- webbing in the leaf (look for it in the above picture)- spider mites. A strong jet of water targeted on the webbing followed by the application of neem oil or a general organic insecticide should help control spider mites.
Well, this is a good start, at least. There is always more to talk about. Check back for more tips in the future.