Question
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Followup To
Question -
The older leaves on my orange trees are yellow and the branches on the middle top of the trees are dying. I believe these are symptoms of a lack of magnesium. I bought your epson salts and I'm not clear on how much to use. I don't want to use too much and kill the trees. How much should I use for a full grown mature orange tree? Should I spray it on the foilage or spray it on the ground?


Answer -
Before assuming magnesium deficiency, check if the plant has developed a severe mite infestation that caused the leaves to yellow and drop off (citrus is very prone to mites under warm, dry conditions) or the plant has a water problem. Mites are very tiny insects. They look like tiny red dots on the undersides of the leaves and create a fine webbing you can barely see in the leaf axils. Often, people don't even know mites are causing a problem since they are so hard to see. Spraying with either a mitacide product or an oil (such as neem) on a regular basis (twice weekly) will help get rid of the pests. However, they are persistent and will return when spraying stops if conditions are still warm and dry.

Both over- and underwatering can result in leaf yellowing. So, making sure the plant gets sufficient water but dries out just a little between irrigation cycles is important

If magnesium deficiency is the problem, sprinkle the magnesium sulfate lightly under the canopy of the tree, or use 1 tbs per gallon of water if you mix it with water.

I bought epson salts since actual magnesium by itself is impossible to find. The instructions are confusing and are for roses, not orange trees. The label says 1/4 cup per 1-2 gallons of water which is suppose to cover 500-1000 square feet for FOLIAR. That doesn't make any sense since I couldn't disslove a 1/4 of a cup with just a gallon of water in a sprayer. For soil application it says to apply 1/4 cup to base of the plant. What is the base? Is that the drip line to the trunk?

1 tbs per gallon. How much should I spray? Until the ground is completely wet around the whole tree (dripline to trunk) or a certain amount of gallons? Can I use too much?

         Thanks

Answer
The instructions on the lable always tend to be on the high side. Several lighter application are preferred to one concentrated application. This is salt, and too much can cause damage to the tree roots. You can not go wrong if you use 1/16 cup 10 times over a period of a growing season, but if you use 1/2 cup in one go you may hurt the roots.

I would use a light sprinkle (1/8 - 1/4 cup) evenly distributed under the canopy of the tree. Do not get closer than 3-4" from the tree trunk, but you can go 1-2 feet beyond the canopy as the roots of most trees extend beyond the drip line.

The best result is had if you snake a soaker hose in circles around the tree and let it water the soil

If run-off occurs (water running away from the tree), stop - wait a few minutes - start again. This will condition the soil to accept water. Soil is like a sponge. If you try to pour water over a dry sponge, it will run right off. If you wet it moderately first, you can then pour water on the sponge, and it will absorb until it has reached capacity. Soil acts in a similar manner.

First wet the soil by running the soaker hose for 1/2 hour or two applications of 15 minutes, 30 minutes apart. Then sprinkle the magnesium sulfate (epsom salt) lighthly under the canopy of the tree, and a little beyond. Restart the soakerhose and run for 30-45 minutes. STOP.

If you do not have a soakerhose, then you can use a gardenhose with a nossle, but it takes time to wet the soil first, and then water enough to allow the nutrients to soak into the soil. It takes patience with a handheld hose.

If you use the above method, you can not apply too much water.

Note: the best source of magnesium for plants are dolomitic lime (unless your soil is already high pH in which case do not use) and magnesium sulfate (aka epsom salt). You would not use chemists magensium on plants.

Kenneth