I asked Pete Duncombe, horticulturist at the Springs Preserve, to answer some questions that have come my way.
Q: Why are my flowering pear leaves turning yellow, scorching and turning black?
A: You are describing a severe iron deficiency. They need iron to keep them beautiful. Our alkaline soils bind up the iron so pears can’t get it. Approach this problem in one of two ways:
Spray iron directly on the sick leaves to regreen them, but this is only a temporary fix. Add dish detergent to the iron solution to spread the iron over the leaves for a better response, otherwise the iron runs off.
To get rid of the problem for years to come, Duncombe advises vertically mulching the tree, that is drilling holes 2 inches wide vertically into the soil. Space the holes 2 feet apart under the entire canopy of the tree.
Duncombe said it sounds like a lot of work but it’s not. The Springs Preserve and UNLV vertically mulch their trees yearly and they’re all healthy looking.
“Purchase a Ross-Root-Feeder and attach it to your garden hose. As the water jets out of the root feeder, it drills the holes for you. Drill them as deep as you can. Finally, fill the holes with compost.
“Vertical mulching does wonders for struggling trees and shrubs. The root feeder opens up your tight soils to dissipate those toxic gases. The compost and microbial activity lowers the soil’s pH to unlock the soil’s iron for better tree growth and water and oxygen peculates deeper into the soil.”
Duncombe strongly urges gardeners to use Iron 138 sold at Plant World and Star Nurseries. Your soil cannot lock up this iron, so it’s always available to your tree.
Q: We planted a 5-foot-tall ash tree and are wondering if we need to stake it?
A: Duncombe questions if it really needs staking? If it stands upright, don’t stake it. Remove the transportation stake coming from the nursery. Don’t remove the small branches growing along the trunk. They strengthen the trunk. You’ll remove them next year.
If you must stake, they immobilize the roots so the roots can spread. Drive stakes into solid undisturbed soil to hold up trees during winds. Holding the trunk, run your hand up until the tree is somewhat vertical. At this point, place ties loosely around the trunk. If there’s lots of top growth, selectively thin out the branches so the winds freely sail through. Prune trees anytime, but keep the trunk shaded to prevent sunburning the bark.
Q: I planted a beautiful salvia greggii in June and it’s gone down hill ever since?
A: It goes semidormant during the heat but will bloom again in the fall, the expert advises. Remove its spent flowers to spruce up the plant.
Q: We just planted two pineapple guavas and are wondering what’s the best way to care for them?
A: Pineapple guavas are beautiful when in bloom, Duncombe says, they must be well nourished with a phosphorus fertilizer to perform as you expect. Phosphorus stimulates new growth to keep blooms coming. Most of them are undernourished. They do best when plants get relief from afternoon sun.
Q: Does blue grama grass grow here? I love the blue color of the grass.
A: Yes, blue grama grass grows here. It’s drought tolerant and requires little maintenance; tolerates some traffic; greens up early and stays green longer into the fall; easy to start by seed; spreads by rhizomes and only needs monthly mowings. You’ll need to order it from highcountrygardens.com.
Q: What are the bugs gnawing holes on my cactuses?
A: This new bug becomes very content on cactuses and quickly multiplies, Duncombe says, so you must remove it. He suggests vacuuming them off. It doesn’t do any good to wash them off.
Q: Why won’t my crepe myrtle trees bloom and is it too late to expect any blooms this summer?
A: Blooms come from the new wood produced this spring. If you are removing this wood it eliminates your potential blooms, Duncombe warns.
Your trees may also be suffering from malnutrition preventing them from blooming. Use a fertilizer high in phosphorous. It is high in phosphorous so plants bloom more. Follow each feeding with a deep irrigation to move the nutrients to the rooted area.
Are your trees getting enough light? They need at least morning sun to bring on the blooms.
Linn Mills writes a garden column each Sunday. You can reach him at email@example.com or call him at 702-526-1495.