Apply annual landscape fertilizer to fix yellowing leaves

Q: I have a bottle brush shrub that is open and getting yellow.

A: The Australian bottle brush plant is sold as a shrub but can reach heights of 25 feet so it can also qualify as a small tree as well. Just don’t use dwarf types like Little John if you want a larger tree-sized plant.

In tree form, it can be used on single-story homes for shade. To be on the safe side, plant it away from hot walls.

There is a weeping form and a nonweeping form as well as dwarf varieties. Also flower color can range from yellow to red and shades of red to pink and white.

Yellowing of the leaves oftentimes occurs when the soil is low in nutrients as well as its organic matter content. Fix yellowing leaves by applying a landscape fertilizer every year in the spring and combine it with an annual application of chelated iron.

Enriching the soil with organic matter is done by raking the small rocks back and applying a thin layer of compost to the soil, wetting it and raking the rocks back. Large rocks may not need raking. The compost and fertilizer will just wash through it into the soil.

To improve the density of its canopy, make sure it gets enough water. The plant grows best if treated as a mesic plant rather than a desert or xeric plant.

Water should wet the soil about 3 or 4 feet in diameter to a depth of about 18 to 24 inches deep each time. Water it as you would any mesic plant such as ash, bottle tree and African sumac. As this plant approaches 10 feet tall, then wet the soil about 5 to 6 feet in diameter.

To get a small tree out of this, remove the lower limbs when it is 3 or 4 four feet tall so that the canopy occupies about ⅔ and the trunk is about ⅓ of its height. Plant it at least 5 feet away from hot walls or it will fry.

Q: If you were to buy one product for insect control on plants, what would it be?

A: Probably soap and water sprays or an oil but not a Neem-type oil. Soap and water sprays are deadly to all insects whether it’s a good or bad insect.

With soap and water sprays “what you spray is what you will kill.” Be careful when you use soap sprays and spray only what you intend to kill. In many ways, it’s like a gun.

The advantage of industrialized pesticides is that they stick around longer after you spray them. Soap and water sprays must be repeated more frequently to protect plants from undesirable insects but are perceived as more environmentally friendly. I always carry a bottle of soap for mixing with water in case I see an insect problem that needs my immediate attention.

In a pinch, you can make your own soap spray by adding about a tablespoon of dishwashing soap to a gallon of water. I prefer using a pure castile soap to mix with water.

The oils I’m talking about are the horticultural oils or dormant oils made from paraffin or mineral oil and not from the Neem plant. These types of oils have been proven to be very effective on soft-bodied insects like scale, aphids, mites and whiteflies. Follow the label directions when making an application.

Q: I am growing a healthy bottle tree in a very large concrete container in Queensland, Australia. The lower branches have been turning brown and then falling off. Is this typical behavior as this tree grows taller or a water problem? I am watering maybe two to three times a week using a handheld hose. We are currently moving into our summer with very warm to hot days.

A: Growing in containers or pots presents its own set of problems (primarily heat, soil and water management) that growing them in the ground does not. I would encourage you to think about planting in the ground if possible. Bottle trees get big.

In Australia, they sometimes call Brachychiton rupestis a bottle tree. In the U.S., Brachychiton populneum is called the Australian bottle tree. Both are natives to you but rupestis gets the typical bottle look when younger while populneum gets a bottle shape that is not as exaggerated.

Dropping of lower limbs may be natural with that species if they get to be 8 years old. Hard to know since it depends on how old it got and if the trunk was starting to swell.

I would suggest growing them in double pots for heat management. The outside container creates shade and acts like a heat protector for the roots. When the sun shines on the pot directly it can damage or kill about 50 percent of the roots due to heating up of the soil.

The surface of dry containers when the air temperature is 105 degrees is about 175 degrees. Plant roots can handle temperatures at about 135 degrees. I tell people to water their plants just before the heat of the day.

As trees get older their roots occupy more of the container and this can be a significant problem during the summer. Root growth occupies space.

Soil in containers wears out (depletes) in about five years and should be changed or amended every three to five years. I would discourage you from growing a large tree (bottle trees mature at about 50 or 60 feet) in containers.

Most containers are not large enough to handle tall trees and their roots as they get larger. Containers are better suited for smaller plants like limes, calamondin and finger limes.

The usual problem with bottle trees is poor drainage and watering too often. The roots will rot if they get a continuous water supply and the soil stays wet. Digging them up when roots are rotting is usually accompanied with a putrid smell as the roots rot.

When watering by hand, about ¼ of the applied water should come out the bottom to remove salt.

If you can’t control the water in the soil (drainage) or the application of water, then plant the tree on a hill that is at least 1 foot higher than the surrounding soil and 6 feet in diameter. Cover the soil with a 2-to-3-inch layer of surface mulch, either rock or woodchips.

Q: I am growing iceberg roses and have noted holes in the petals of the flowers. I have taken this problem to nurseries, and they are stumped. Do you know what causes this?

A: The shape of the damage to the petals can give some clues. If the shape is circular and smooth, or near circular, then it is probably damaged by a leaf-cutter bee. These bees cut holes in flowers that are nearly circular and about the size of a dime. They are great pollinators when they are active.

Since these are solitary bees and the female cuts these circles for egg-laying, they start showing up when it gets warm, in about April and then through the summer. That’s why they make good pollinators for apples, pears or other late or continuous bloomers.

You will not see these near-perfect circles show up until that time. If the holes have jagged edges around their outside, then most likely it’s a chewing insect or possibly snails/slugs.

You will have to do some detective work if the holes are not from leaf-cutter bees. Snails and slugs are the easiest to detect because they’ll leave a slimy trail on leaf undersides when they do their damage.

If you think it’s snails or slugs, then spread out wet newspaper or cardboard just before nightfall. They like darkness and moisture, so the dark and moist undersides make perfect traps. Squeamish fingers will pluck them from this underside for execution.

If it’s not snails or slugs, then make or buy sticky traps. These can be made by hanging yellow sticky 4-by-6-inch business cards close to the damage and covering them with a sticky substance. Smeared Vaseline jelly will work but not Vicks.

Q: Should I turn off the water to my yuccas during the winter?

A: I would not. I would water them once during the winter months of December and January. That is the time to give them a good soaking.

Q: Why do you encourage people to avoid planting during the winter months? I can understand it in Minnesota but why Nevada?

A: Simply because I don’t know what is going to happen. If it is a warm winter, then planting during the winter is OK. But if it is a cold winter, such as the lower teens at night, then be careful.

Plants need soil at least 45-50 degrees to grow roots. Otherwise, the roots just sit there until the soil warms. If the plant is winter tender, like bougainvillea or most citrus, then you are playing Russian roulette with the winter temperatures.

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.