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Over Fertilizing

I used too MUCH fertilizer on my mums, now all the leaves are turning brown. They just look burned. Is there anything I can do to save them?

You have probably experienced eating something very salty and then being very thirsty for a while afterwards. Well, fertilizers are salts and when you apply too much it not only prevents the plant from absorbing water, but may actually draw water from the plant. Thus your plant gets very, very thirsty. This thirst causes burning of the roots and yellowing and scorching on the tips of the new leaves and shoots. In fact, one of the most common symptoms of high levels of salts is browning of the leaf edges. Being under this high stress also opens them up to root and foliar diseases. Once this happens, there is no easy answer.

If the fertilizer was applied on the top of the soil, you can try to rake off as much as possible. Then water deeply and heavily several times to get the salts to move down and out of the soil layer that the roots are in. Once the soil salt level is back into proper perspective, the plant can begin the process of taking up water, growing new roots, and repairing the damage to its leaves. Of course, if the damage was extensive it may never recover. You will just have to wait and see.

In order to prevent fertilizer burn in the future, there are several things that you can do. First try using a slow release fertilizer that slowly delivers nutrients over the course of 3 months. Reapplying every 3 months may be a little more expensive up front, but this provides for healthy plants and more even growth as the food is released slowly and consistently over a period of time and there is less likelihood of fertilizer burn from too high an amount applied and available at one time. High concentration, quick release fertilizers provide for fast, lush growth but in the wrong amounts can be deadly and dead plants are very expensive. And the soft, lush growth they cause provides an ideal climate for pests and disease causing organisms. Also, soft, lush growth is not as stable under adverse environmental conditions such as drought, wind or hardiness.

Make sure you read the directions on the package of fertilizer you purchase and apply the proper amount spreading it completely and evenly in a wide area around each plant. This is especially important if you choose to use a quick release formulation. Fertilize only when the soil is moist and water in very thoroughly afterwards. If it is possible to work it into the soil without disturbing the roots too much, do so.

Be sure to test your soil if you are suspicious of too much salt, especially in containers. And if you see salt building, which is a white crustiness on the soil surface or around the edge of the container, leach them heavily with multiple watering, until the water that runs out of the bottom of the container is clear. And in every case, if using granular fertilizer, don’t get it on the plants or in direct contact with the roots.

Organic fertilizers and compost are less likely to cause over-fertilization as they require the soil microorganisms to provide nitrogen and other nutrients as a byproduct of their munching on these components, making them slow release fertilizers.