Q: If I prune my old oleanders this fall, will they bloom this coming spring?
A: It depends on how they were pruned and the type of fertilizers applied. Oleanders flower on new growth.
If oleanders are cut to the ground, they first shift their growth to replace leaves and stems that were lost. This is so they collect sunlight for future growth first. In doing so, they replace what was lost before they begin flowering. Producing flowers and seed takes a lot of energy.
Depending on the amount of growth after pruning, they may or may not flower the following year, but they will flower in year two and onward until they are pruned again.
If they are cut back moderately, they will probably flower immediately after new growth appears in the early summer, a few weeks after pruning. There may be a slight delay in flowering, depending on how much of the plant was removed during pruning.
Flowering might be delayed by adding high-nitrogen fertilizers. Making lots of nitrogen available to plants encourages leaf and stem growth first, which delays flowering. Applying reasonable amounts of high-nitrogen fertilizers should not reduce flowering, but when it is applied in combination with severe pruning, it might.
Two approaches used when pruning shrubs is renewal pruning and rejuvenation pruning. Renewal pruning leaves a substantial number of smaller stems remaining after pruning. Only a few larger stems are cut back to the ground.
Use rejuvenation pruning if a tangled mess of growth cannot be easily pruned or there is substantial winter damage. This technique removes all growth to a few inches off the ground. Replacement growth occurs from the remaining stubs left after pruning. Rejuvenation pruning causes the biggest delay in flowering.
Q: I see resorts with gorgeous masses of jasmine, and in many places, they are pruned into low mounds for borders. How do I avoid having the woody, exposed leggy stems showing? Will the plant regenerate itself if I simply prune it all the way to the base? What time of year to do that would work?
A: Star jasmine performs best as a vine, rather than a groundcover or shrub, but it can be used in a variety of ways if given enough room to grow and carefully managed.
The picture of your star jasmine shows it planted a few inches from the brick or concrete pavers. Star jasmine is a medium-sized plant that can grow 2 feet tall and 10 feet wide if left to sprawl.
This means plant spacing should be 5 feet apart to totally cover an area. It should be planted about 5 feet from pavers, not a few inches.
Light pruning can be done anytime, but the best time to prune to optimize flowering is after they finish flowering in late June or July. Pruning then gives the plant a chance to rebuild itself for the next flowering cycle, which should begin in late spring.
Star jasmine can be cut back very hard so that 4 to 6 inches is sticking out of the ground, and it will regrow into a plant full of new growth and flowers. Pruning it as a vine is different. After pruning, apply a light fertilizer application (a rose or tomato fertilizer will work) and water it in.
Q: Is it too late to treat my shrubs for grubs this season? I’ve lost several Indian hawthorn shrubs and several agaves to them during the summer. What is the best time and way to apply?
A: Most information circulating on the internet tells us that grubs are immature forms of specific beetles, usually June beetles. Here grubs might range from scarab beetles (June bug) to snout beetles (weevils) to dung beetles and even flies and moths.
All these different kinds of insects have different life cycles which produce grubs at different times of the year — some at multiple times per year. Many times, we call these types of grubs “white grubs” when they aren’t.
The best time to eliminate them is when they first begin feeding on plant roots as baby grubs. This would be midspring for these types of grubs.
To get good control, the grub should be present and just started feeding. Organic control measures like bacteria and nematodes are quite specific to the type of grub, or it can apply to all the grubs, as it does for some insecticides.
In your specific case, the Indian hawthorn probably has grubs from a type of June beetle, and the agave grub is probably from a weevil or snout beetle. The Indian hawthorn grubs might be controlled with an organic application of milky spores (Scotts GrubEx) in late March or April.
Control the grubs in the agave with an insecticide poured over the top of it so that it runs inside the crotch of the leaves. Apply it to the soil twice: once in April and once in May.
Q: Our subdivision is disgruntled with our current landscape company, as we have 30 bad lawns out of 68. People living here since 2000 say it is the worst. Do you know any companies with a good reputation?
A: This type of question is sent to me quite often and a common complaint from HOAs. The company you privately mentioned to me, generally, has a good reputation. I know areas of town it is servicing, and I have heard no complaints.
Large landscape maintenance companies send crews on specific routes. These crews have supervisors. Maybe it’s a supervisory problem, rather than a company problem. Call the company and initiate a discussion about the problems and see if these can be rectified before moving to a new company.
Q: I have a 3- to 4-year-old crape myrtle that had a lot of flowers this summer. Now the leaves are dark green on the top part but beige or brown on the bottom part. It almost looks like the leaves are burned. The watering habit hasn’t changed. Do you know what the problem would be?
A: That description fits a water shortage to the top of the tree. This could be from not enough irrigation water applied; collapsing soils that suffocate roots and cause them to die slowly; watering too frequently, which also causes roots to die slowly; and damage to the tree trunk, which causes drought and damage to the leaves. All these problems cause leaves to turn brown along the edges.
Follow the KISS principle. Check the tree trunk for physical damage. Borers can cause this damage as well as people. If this is the cause, reduce the size of the treetop by eliminating entire limbs that are not necessary. Reducing the canopy reduces the tree’s need for water.
As trees get bigger, they need more water. Water required by this tree after four years will increase to about 15 to 20 gallons each time you water. If the water is on for one hour, then four or five drip emitters are needed that deliver 4 gallons each hour so the tree gets 16 to 20 gallons each time the tree receives water.
Place emitters 2 feet apart under the tree’s canopy and water at least half the area under its canopy. Give the tree at least a one-day rest when it receives no water at all during the hottest months. Give it more rest days when it is cooler.
Rock on top of the soil can, after about four years, cause this kind of problem. Plants like crape myrtle that are originally from wetter climates and different soils may have a tough time in our soils without some soil amendments.
Soil amendments used at planting time run out of steam in about four years. In other words, they are gone. Rocks covering the soil surface do nothing to replenish the depleted organics.
If the soil around it is covered in rock, rake it back about 5 feet. Then cover the soil first with about 1 inch of compost (about 2 to 3 cubic feet), water it in thoroughly and finally cover this with wood chips 3 to 4 inches deep.
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.