Leaves will help tell story of plants’ health

Q: Do desertadapted shrubs like Texas rangers, cassias and others benefit from adding sulfur to the soil? Will they perform better in a pH around 7.5 as opposed to 8? I know it’s probably not necessary but I’m just wondering if the additional sulfur in the soil will help them thrive better or if it’s overkill.

A: We have to remember that the pH scale is exponential, like the scale used to measure earthquakes. So changing the pH from 8 to 7.5 is a huge change. Our soils are chock-full of calcium carbonate or lime that wants to force the soil to a pH around 8.2.

Because there is so much lime in our soils, lowering the pH is always just a temporary solution to the pH problem.

Yes, sulfur in moist, warm soils will slowly bring pH down from 8 to some lower value. So will decomposing organic matter. Mineral sulfur (not sulfates) will produce acidity as the sulfur changes to the sulfate form.

When most of the sulfur has been converted to sulfate, the pH will begin to rise again rather quickly. Then you apply more sulfur and it will work again in the same manner.

When organic matter is mixed in the soil and is decomposing, the microorganisms responsible for breaking down this organic matter release carbon dioxide. This carbon dioxide mixes with soil water and produces carbonic acid, which also lowers the soil pH. However, it also only works in warm, moist soils.

The question becomes: Is it really necessary? In some cases, probably not. The pH of the water conducted from the roots to the leaves of most plants is about 6.8. So any time you can keep the soil close to pH 6.8 you are better off.

Some plants are fussier about soil pH than others and demonstrate this fussiness through problems such as leaf yellowing because of iron chlorosis. These fussy plants need the soil modified with sulfur or organic matter or the additions of iron in a form that works at a higher pH. At a pH of 8, the only chelate applied to the soil that really works is EDDHA. This is the reason I mention it so often.

Many desert plants would prefer to have their roots surrounded by a soil at a pH of 6.8 but can tolerate soils much higher than this. Plants not from desert soils, like photinia and Indian hawthorn, apparently do not handle soils with a high pH very well.

What can you do? The plants you mention are tolerant of desert soils and probably will not have these kinds of problems.

Watch your plants. If they are having some problems (yellowing of leaves, unhealthy weak growth) and you have planted them correctly, watering and fertilizing them, then apply some sulfur or wood mulch at the surface that will decompose and let the soil slowly adjust its pH during the warm months.

If they are doing well without it, then don’t bother. If yellowing leaves are the problem, then apply the iron chelate, iron EDDHA, to help get iron inside the plant in a form it can use. I would do it case by case.

Q: I have a dwarf Rio red grapefruit tree and a dwarf Valencia orange tree, both from mail order. They are 2 years old and about 3 feet tall. The grapefruit produced in 2011 and 2012. The fruit was great. The orange has not produced so far. This winter I thought I lost both because of the cold but they came back strong and look wonderful except for some yellowish leaves. The problem is they are very bushy and crowded with some branches touching the ground. I feel they need to be pruned. I found a lot of information on how to prune the trees but when to prune is conflicting.

A: In the desert it is a bit trickier because of our high light intensity and potential for sunburn if we prune too much at the wrong time. But the bottom line is this: You can do some pruning any time of the year, but only do aggressive pruning during the winter months. Or, if you have fruit on the tree, wait until after harvest and prune then.

On citrus you want to prune after harvest but before it flowers again. The other thing about citrus is that it can be damaged by winter cold, as you know. It is best if you can wait until you are pretty sure most of the cold has passed and then prune it. This way if there is some cold damage, you can remove it at the same time as you prune.

Q: I wonder if you can help me diagnose a problem with my camellia, Marie Bracey. I had it in a container but moved it to our backyard where it gets the morning sun and afternoon shade, which is what the card that was