Yellow leaves not necessarily caused by fertilizer

Q: I see many times where you’ve said fruit trees only need feeding in the spring. However, without periodic applications of nitrogen, my 3-year-old peach tree leaves become yellow. Could there something going on I should investigate?

A: Yellowing can be from lots of different things, not just fertilizer. If enough fertilizer is applied in the spring, you should get dark green leaves and lots of new growth. Enough for the whole year. You want lots of new growth in the spring and the fertilizer to slowly disappear from the soil. This should take about two months.

There is one reason why you might apply fertilizer frequently to plants — extremely sandy soils. This soil would be like planting in a sand dune. I haven’t seen any of it in Las Vegas, but I have in Bullhead City, Arizona. When the tree is planted in extremely sandy soils, fertilizer is applied lightly every couple of weeks and water daily, sometimes twice a day.

Running out of fertilizer in a couple of months from a spring application gives the tree time to set up fruit production for the next year. Fertilizing the tree continuously pushes lots of new growth but may cause low fruit production. The tree sets up its fruit production for the next year any time from about late June through September. It depends on the fruit tree.

The tree should grow about 18 inches each year when they are young and established. No more than that. Excessive growth is frequently caused by overapplying fertilizers. Too much growth and it’s just wasted since it is cut back during winter pruning. After fertilizer is applied in early spring, the tree will grow dark green leaves for the first two months and then the leaves will become a lighter shade of green as the season advances, but they shouldn’t be yellow.

If yellowing is caused from a lack of nitrogen fertilizer, the older leaves become yellow, not new leaves at the ends of branches. If yellowing is caused by a lack of a micronutrient fertilizer such as iron, yellowing appears in leaves at the ends of branches. The yellow leaves in both cases becomes worse as the season progresses unless the correct fertilizer is applied to correct it.

Yellowing leaves can be from watering too often or poor soil drainage, or both. This leaf yellowing also appears at the ends of branches, like iron. Yellowing can be from planting too deeply. The tree should be planted the same depth it was in the container or grown at the nursery.

Yellowing can be caused by early borer damage. Borers damage the trunk or limbs by their feeding, which interrupts the flow of fertilizers, like iron, to the leaves. Because the leaves lack iron, they turn yellow.

Investigate all these possible situations before jumping to the conclusion it’s a lack of fertilizer. If you’ve applied your spring application of fertilizer and the leaves are dark green, it’s not a fertilizer problem.

Q: I’m growing a saguaro cactus in my yard, and it’s developed a black spot on its surface. Do I need to be concerned?

A: Yes, you should be concerned. As you know, this is not saguaro country, so our location poses some problems when growing saguaro here. At planting time, make sure the soil drains well and amend the backfill around the roots with a small amount of soil amendment. Be very careful not to damage the plant in any way when planting.

First, let’s find out if there is a problem or not related to that black spot. Take a sharp, sanitized knife and cut the black spot out of the saguaro. Look at the flesh inside the cactus and under the black spot you removed. If the flesh is green and clean, there is no problem. Leave it alone and let it heal. It will.

But if the flesh under the black spot is black or brown and oozing like it’s rotting, then this could be a problem called bacterial necrosis of saguaro. If this infected black spot is low on the saguaro, there may be nothing you can do except wish it well and hope for the best. But it will probably die.

If this disease is caught early and all the infected flesh is removed with a sharp, sanitized knife, there is a good chance it will heal and recover.

This disease spreads easily from infected plants by insects landing on open wounds or being careless during planting. So be very careful not to damage the plant in any way during planting.

Q: What is the best way to prune bougainvillea? Do I cut back the top branches? Or just leave it alone? I see new growth at the base of the plant.

A: Pruning depends on how much of the bougainvillea died back during the winter. It’s tropical. Bougainvillea is damaged at the slightest freezing temperatures. If freezing temperatures occurred during the winter for any length of time, the plant probably is dead to the ground. New suckers appear at the base of the plant and can regrow from this crown.

New growth from the trunk or collar signal where the pruning cut, or cuts, can be made. Wait for strong new growth to appear and make your cuts just above strong growth. Sometimes there will be an inch or two of weak growth followed by strong growth beneath it. Cut it just above the strong growth and remove the week growth as well as anything that’s dead.

In climates where it doesn’t freeze, bougainvillea can be quite large and is grown as a shrub, trellised or pruned back.

Water and fertilize it and it will come back like gangbusters.

Q: I’m ready to buy five fruit and nut trees. I listened to the podcast from your blog and narrowed them down to an almond, a pistachio pair, a Babcock peach, a Santa Rosa plum and a Flavor Delight apricot. Where are they available for purchase?

A: Good selections but it is approaching the end of fruit tree planting season soon. When air temperatures get hot, trees will struggle to get established. The best time for planting fruit trees starts in about mid-January. Get fruit trees planted as soon as possible.

A good almond tree to get — and I’ve seen it available here — is All-in-One. I have grown them, and they are a good producer and dwarf compared to the size of other almond trees. Other almonds will work here just fine and grow very well, but they will be a standard size.

Pistachio trees start producing nuts slowly compared to almonds. Expect the trees to take four or five years and a fairly good size before they start producing nuts. They are very productive, but they can get big. So, plan on giving them a little bit more space.

Babcock is a good, freestone white peach with excellent flavor and aroma with fruit ripening about mid-July. June and July are good months for peach.

Santa Rosa plum is a good old-fashioned purple, soft plum that’s also an excellent pollinator for many pluots. Flavor Delight is an aprium, not an apricot, but the fruit looks and tastes just like an apricot but better. The tree stays small compared to apricot. It’s an excellent choice.

I think you will find all of them locally except for the aprium. People don’t know what they are yet, and they don’t recognize the name. They will before long.

Make sure tree holes are dug and the soil amended before you bring the trees home. They will need a minimum of 10 feet between trees, so they don’t crowd each other. At these spacings, they will need to be pruned to keep them smaller. Give the pistachios a bit more room.

Plant them early in the morning when it’s cool and make sure that when they are gently eased from their containers, they are planted directly into wet soil without lingering. Thoroughly water them in with a hose two or three times and then turn them over to the drip system.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.