Leaves will help tell story of plants’ health

Q: Do desert-adapted 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 attached stated. It was growing fine but now there are about 30 leaves that have brown tips.

A: You are fighting an uphill battle growing camellias in the Las Vegas Valley since they require similar conditions to azaleas and rhododendrons. There are camellia societies, the counterparts to rose societies, on the southeast and west coastal areas and inland in Northern California. It’s not that you can’t do it, but it will take quite a bit of care on your part.

You have the Japanese camellia type. These plants are medium to large shrubs and even can be trees so it may take some time for them to get big enough to flower.

Camellias do not come from desert s. This will give you some insight as to what you will have to do; improve the soil a lot and give it some protection from our harsh desert environment.

You did that by following the card attached to it. But just a warning: That growing instructions card was not intended for Las Vegas but for friendlier camellia environments so you may need to take what it says further. Even morning sun may be too intense for it if it extends into late morning and thus may contribute to the browning of the leaf edges.

Other things that can contribute to leaf scorch are poor soil conditions and salty water coming from Lake Mead to our taps. Those people with well water frequently have much better water than the water coming from our taps.

Another problem you will most likely have will be yellowing leaves. Camellias like the soil to be slightly acidic and our soils are not. This will mean that iron will be tough for the plant to get in a form it can use.

The only way to provide that kind of iron is to make the soil more acidic or give it iron in a form it can use. Lots of decayed or decaying organic material will help in the soil around the roots and on the soil surface on top of the roots.

Usually the more effective way to apply iron is to use chelates. Like the broken record I am, the chelate EDDHA combined with iron is the most effective way for iron to reach the plants in our soils.

Sulfur applications also will help but the sulfur should be pulverized into a powder, not like little rocks, if it is to be effective.

So what to do? Make sure the plant had lots of good compost mixed into the soil at planting time. If you are not sure, replant it carefully this fall around the first week of October.

Mulch the soil surface with organic or wood mulch. This is important with camellia since it has a shallow root system. Find a place that gives it early morning sun and not late morning sun, is out of strong winds and not near a hot wall. Filtered light from a tree that allows scattered light on the ground with plenty of air movement (but not strong wind) would even be better but not total shade.

Next spring, after all danger of frost has passed (usually around the first to the middle of March), fertilize the plant with an azalea or rose fertilizer and add iron chelate as well. Expect that your camellia will not be picture perfect since it is not growing in an ideal climate and soil.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.