A quiz I wrote a few weeks ago was so popular with readers that I thought I would quiz you with more questions, but this time focused on what to do in the fall.
Q: Are the cooler fall months the best time to plant trees and shrubs?
A: It depends. Divide the available trees and shrubs into two groups: those that are winter hardy and those that are winter hardy. The best time to plant winter hardy trees and shrubs is in the fall, from late September to mid-November.
The warmer air and soil temperatures of fall and spring give these plants two âspringsâ to establish themselves before the heat of summer. The worst time to plant winter trees and shrubs is in the fall due to the risk of frost in December, January and February.
This recommendation depends on our winter and our landscape. Sometimes we have winters that don’t freeze at all. Sometimes we have winters that barely get below freezing. Every now and then we get a hard frost with winter temperatures well below freezing, up to the teenage years and even below.
I recommend trees and shrubs which are important design features of your landscape to withstand temperatures up to 20 degrees, 12 degrees below zero. There is a good chance that established trees and shrubs will recover from rare frost events. On rare occasions our landscapes can get colder than this.
Q: What is the best fertilizer for roses in the fall.
A: The worst months for roses growing in the hot desert are those 3 and a half months of hot summer. Our 3.5 months of extreme heat are brutal for landscape roses, and they need a chance to recover as soon as the air temperatures start to cool.
The planting months in early fall are also the best time to fertilize roses with the same fertilizer used in spring: high in phosphorus and potassium with lower amounts of nitrogen. The instructions on the fertilizer bag recommend the maximum amount of fertilizer to apply.
If your roses have dark green leaves, lots of growth, and ready-to-pop flower buds, halve the recommended amount to apply. Some Rosarians like to use Epsom salts – for magnesium content – as part of their fertilizer blend.
Roses like compost and wood chips, not stone. Roses work best surrounded by rotting wood chips with compost mixed into the soil.
Be aware that there are two types of compost available, including rich compost which is packed with fertilizer. Rich compost usually consists of recycled animal or human waste that has been composted.
A 1 cubic foot bag of compost will treat four standard roses. Rich compost does not need an application of fertilizer. Other types of low-nutrient compost likely will. Apply all fertilizer and rich compost within 12 inches of established plants.
Q: Is spring the only time to deeply fertilize trees and shrubs?
A: Not necessarily. Inexpensive venturi type fertilizer injectors such as EZ Flow are becoming more and more popular and are probably the best way to fertilize winter hardy landscape plants. The old-fashioned way of periodically applying granular fertilizers depending on what you are growing is probably the most cost effective method. Both methods work.
If you are using a fertilizer injector, there is no reason to deep fertilize trees and tall shrubs. But if you are using the old-fashioned way of applying granular fertilizers by hand, then deep fertilizing landscaped trees and shrubs is one method that you may or may not be interested in.
Deep fertilization of trees and shrubs was first designed for mixed landscapes where trees and shrubs grew in lawns. The method avoided killing the lawn in places like dog urine does.
If your trees are in mulch and not in a lawn, just drop a handful of fertilizer where the drippers are and the fertilizer doesn’t need to be placed deep. The water from the drippers helps move the fertilizer to where the roots are actively growing.
Q: If you had to buy an insecticide that would treat as many pests as possible in a landscape, which one would you buy?
A: Probably dormant or horticultural oil. It is an oil applied in the middle of winter, after the leaves of deciduous plants have fallen, which suffocates many insects and prevents them from being a problem months later. It is a preventative application, so when used the results are usually not noticed.
A second insecticide I would use is just old soap and water mixed in a spray bottle. Neither is technically organic by definition, but they both work.
Dormant or horticultural oil is sprayed all over the plant, from top to bottom, after the leaves have fallen and pruned. Spray on a warm, windless winter day.
These types of oils are used to control outbreaks of soft-bodied insects like aphids, mealybugs, mites, whiteflies and others. It doesn’t control that bug or those crazy larvae that feed on roots in the soil. But, like many organic sprays, it’s a blind killer: both good and bad are killed.
I had to include the second mixture of insecticide, soap and water because it is so effective. It also doesn’t distinguish between good bugs and bad ones – it kills whatever you spray.
I was taught years ago that it kills by drowning the insect. But the insect’s waxy outer layer is also damaged.
A tablespoon of liquid soap mixed with a gallon of water is a very toxic combination when the pests are sprayed directly. But like many natural sprays, there is nothing left, no residue, after spraying. Frequent repeated sprays are necessary when insect problems persist.
Q: Is this the right time to seed the damaged areas of my lawn?
A: Now until late October or maybe mid November (if it stays warm) and the lawn is cool season fescue type. But if your lawn is made with low-water-consuming hybrid Bermuda grass, bison grass, zoysia, or any other warm-season grass, then you’ve missed the time to fix the dead spots. If this is a warm season lawn, seeding, spreading or hooking up for the establishment by the fall should have been done in late July or maybe even early August.
But you are not too late to fix the dead spots. You still have time to overseed your lawn with perennial ryegrass (I said perennial and not annual ryegrass) for the winter months and then repair your warm season lawn in the spring around April or early May. .
Perennial rye is much prettier and mows better than annual rye. But both will work. Annual ryegrass is for the price conscious, and perennial ryegrass is for those who focus on beauty rather than price.
Q: When can I start pruning?
A: Light pruning can be done at any time of the year, even in the height of summer. Tie your pruning shears to your pants or belt every time you go out into the garden. But heavy pruning should only be done when the plant stops growing. For the most part, the plants have stopped growing by mid-fall, but the leaves have not yet fallen.
What do I mean by lightweight pruning? Light pruning is simply cutting or pruning small diameter stems or branches. Pruning with a hand pruner can be done at any time, but not excessively.
Do not open the tree for sun damage. Heavy pruning occurs when something larger than a hand pruner, such as a pruner or saw, is used for the cut. This should only be done during the cooler winter months and best after the leaves have fallen.
You can prune woody plants before the leaves drop if the plant has stopped growing. Pruning invigorates a tree and makes it grow if it is done too early. But after the leaves fall, you can see the architecture (limb structure) of the tree and make better and faster decisions.
October and November are the time of year when the plant has stopped growing but has not shed its leaves. You can safely start pruning now if you can see what you are doing.
Bob Morris is a horticultural expert and Professor Emeritus at the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send your questions to [email protected]