It's About Time for Dormant Oil Spray

Now is the time to use dormant oil spray.
I always choose a brand that is approved
for organic gardening such as
this one formulated with canola oil. 

Here we are with yet another thing to do in the winter garden! Who said there is nothing garden-wise to do in the winter months?

In the past few days I posted that it is time for bare root planting, and pruning here in the High Desert. And now, it is also time for dormant oil spray, which is also known as horticultural oil, pesticidal oil, superior oil and natural oil depending on the formulation and brand. Those plants especially in need of dormant oil spray include fruit trees and vines, and deciduous trees and shrubs – especially those prone to certain insect issues.

Dormant oil is considered an ecologically friendly way to manage garden insect pests and consequently, some diseases. Many available oil products are made from mineral oil, but there are others made from vegetable oils such as cottonseed, canola, or soybean. These oils are usually mixed with some kind of emulsifying agent, which allows it to be mixed with water and used as a spray.

Dormant oil, used at a time when the plants are dormant or resting, is a good way to reduce pest numbers during a season where pollinators are not present. Insect pests such as aphids, mites, scales, leafhoppers, mealybugs, thrips, whiteflies, caterpillar eggs, and others tend to overwinter in the various cracks and crevices of the plant’s trunk and branches.

Dormant oils work by suffocating the pests by blocking the spiracles through which the insects breathe. The oils can also disrupt the metabolism of insect eggs and the ability of some insects to feed. Many insects such as aphids vector diseases, so by controlling the aphids, some diseases may also be controlled.

Dormant oils should be applied just before the leaf and/or flower buds show signs of swelling or breaking open. You don’t want to spray too early or the insects won’t be active and breathing.

Dormant oils should not be applied in freezing temperatures or when the temperature is over 100 degrees F. During freezing temperatures, the oils don’t hold together well and coverage becomes uneven. If the plants are drought-stressed, they can be more susceptible to damage from the oil. The oils should also not be sprayed on windy days or when it is raining. Some lighter versions of these oils can be used in the summer months, but extra care needs to be taken to not burn the foliage. Some species of plants, including redbud, smoketree and spruce, are sensitive to dormant oils and are usually listed on the product’s label.

Dormant oils are fairly safe and are not poisons, but are still considered pesticides and should always be used according to the label’s instructions. Use only when absolutely necessary as it can kill both good bugs and bad bugs. It is considered safe around humans and pets because it has no toxic residue.

Pruning Tips for High Desert Plants

A couple days ago I posted that it is bare root planting season. It also happens to be pruning season here in the High Desert. There are a number of reasons for pruning plants — producing more or better flowers, developing or maintaining a desired shape or appearance, reestablishing balance between roots and branches, training young plants, rejuvenating older or neglected plants, removing dead or diseased wood, and repairing or removing damaged wood.

The pruning tools available are varied and run from really cheap to very expensive. In my opinion you get what you pay for, so a good approach is to buy the best quality tools that you can afford. Some of the quality brands that are readily available include Corona, Fiskars, and Felco to name a few.

Maintenance of tools is very important for good pruning and the longevity of the tools. When sharpening your pruners, use a file, not a stone, and maintain the original beveled angle. Have a professional sharpen your saws.

Clean your tools after each use. Wipe the tools with an oily cloth – there are some products made for cleaning tools such as Corona’s CLP. Use linseed oil on wooden handles to help keep them in tip-top shape. Use a solvent to remove sap. If you have been pruning to remove diseased branches, soak the tools in a solution of nine parts water to one part bleach between each cut. Keep in mind that the bleach can be corrosive to the tools so make sure to lubricate the tool(s) afterward.

It is always a good idea to have a certified arborist come in to do big pruning jobs such as trees, or anything near power lines. Also, don’t forget safety gear such as leather gloves and goggles.

Before pruning a plant, it is important to know how it grows. Trees and shrubs grow each year from the ends of branches (terminal buds) and the side branches (lateral buds). The terminal buds determine the direction and rate of growth. Lateral buds form branches and twigs that fill in the framework of the major branches. Dormant buds are less obvious and only grow when injury occurs to the terminal or lateral buds. A key to good pruning is learning how to take advantage of the lateral and dormant buds to redirect or rejuvenate plants.

Normally, terminal buds grow faster than lateral buds because of a chemical they produce to retard the lateral growth. This is really strong in young trees and less so in shrubs. Cutting away the terminal bud allows the lateral buds to start growing more aggressively.

When making pruning cuts, the rule is to prune back to a branch or bud and don’t leave a stub (or hat rack), which will die back and cause decay or disease, not to mention being unsightly. Pruning cuts should be no more than a quarter-inch above a bud or side branch. Pruning cut angles should be at 45 degrees and tilted in the direction the bud is pointing. Plants all have buds facing inward and outward. You want to cut to a bud that is facing outward, which results in the plant having attractive outward growth rather than making a tangled mess by growing inward.

Plants that should be pruned in winter (late January, February and into March in the High Desert) include fruit trees, certain roses, broad-leafed evergreens, most trees, vines and some flowering plants.

There are generally three accepted systems for pruning fruit trees – central leader, open center and modified leader.

Apples and pears should be trained with a central leader, which forms strong side branches and one main trunk. Remove some branches growing from the trunk to maintain open space between limbs. Also, thin the secondary branches growing from these limbs in order to allow sunlight and air to reach the center of the tree. Eventually, you might want to switch apples to the modified leader method as it tends to be easier and is close to the way they want to grow naturally (see the Principles of Pruning Guide mentioned at the end of the column for details).

Fruits that should utilize the open center or vase method include quinces, cherries, crabapples, plums, peaches, nectarines and apricots. This system eliminates the central leader and allows plenty of light and air into the tree’s center, but makes for weaker branches so it is not recommended for apples or pears. Try to avoid having all of the branches arise from nearly the same point.

Many fruits such as pears, apples, plums and cherries produce their fruit on stubby growths called spurs. These spurs should not be eliminated or you will not get fruit, however thinning them is recommended.

When planting young shade trees all you need to do is trim off some of the twiggy growth that won’t be a part of the tree’s framework of branches, and twigs that are dead or broken.

Mature shade trees should only need maintenance pruning to remove dead or damaged wood or perhaps a little thinning to allow air and sunlight into the crown. Always cut limbs back to a live branch or main trunk. Cuts should be made just outside (one-quarter of an inch or so) of the branch collar (usually an obvious swelling or wrinkled area at the base of the branch). If you are trimming a large branch, use a three-cut method to reduce tearing of the bark (see photos).

Shrubs should only be pruned for maintenance. Occasionally a shrub may get too tall or broad and may need to be cut back. If it’s a flowering shrub, you need to know if it flowers on old wood or new wood. If it blooms on old wood, you want to prune it right after it flowers – examples include lilac and forsythia. If it blooms on new wood, winter is a good time to prune – examples include butterfly bush and crape myrtle.

Broadleaf evergreens, such as oleander, olive, cotoneaster, privet, euonymus and Pyracantha generally need very little pruning and are often better off if you leave them alone. The only pruning should be to remove dead, diseased or damaged wood whenever it occurs, and prune back branches that get too long.

Vines should be pruned to keep them within their bounds. If you want them to stay compact, prune terminal growth during the growing season. If you want them to ramble, cut to the base all but three or four of the strongest branches. Most flowering vines bloom on last year’s wood so avoid pruning in winter or early spring or you won’t get any flowers.

Most roses bloom in late spring, a little during the summer and again in the fall in this area. If you are pruning a newly planted rose from a container, you should only need to prune away broken or damaged growth. If it is a bare root, you will need to prune away broken or mangle root tips and twiggy growth from the top of the plant.

For maintenance pruning of roses, begin by removing dead, diseased or damaged canes. Next, prune out branches that rub together, and crossing growth in the center of the plant. A general rule of thumb is that when pruning is done, the remaining skeleton should be a vase shape (or you should be able set a small bucket inside the framework). On roses three years old or more, you should prune away about one-third of the oldest growth, then cut one- and two-year-old canes back to the height you want to maintain.

For more complete information, including diagrams, Corona Clipper (my source of information) puts out the Principles of Pruning guide, which is available for free at http://info.coronatoolsusa.com/corona_principles_guides

Use the three-cut method when sawing off large branches

1. Make an undercut at least
6 inches from the bark collar.

2. At about an inch beyond the undercut,
remove the limb with a top cut.

3. Remove the remaining stub with
one smooth cut from top to bottom
just outside the bark collar.

NOTES:

Types of pruning tools:

• Bypass- or anvil-style hand pruners: Bypass works like scissors and tend to give a better cut. Anvils can come with a ratcheting mechanism that makes it easier to use. Hand pruners come in various sizes that can cut branches up to three-quarters of an inch in diameter.

• Loppers: These are great for larger sized branches. Loppers are similar to hand pruners except that they have bigger blades and much longer handles for additional leverage, and depending on the size, can handle branched up to three inches in diameter.

• Hedge shears: These are designed with long, scissor like blades. They should be used for clipping soft young growth – never use these on harder wood.

• Saws: Bow saws are lightweight and are intended for medium sized branches. Other pruning saws can have a straight or slightly curved cutting edge. These usually cut on the pull, rather than on the push, making the work much easier. Sometimes saws are designed to be folded, making transport and storing easier and safer.

• Pole pruners: These are handy for high work, but be careful to stay away from power lines. These can be a hook and a blade similar to hand pruners, or it can be a saw, sometimes a combination of both. These are usually at the end of a long pole, generally 10 to 14 feet in length, sometimes extendable.

• Of course there are all kinds of power tools available.

It's Bare Root Planting Season

Here it is, almost February - a new year has begun - and this means it is bare root planting season. Generally speaking, bare-root plants are available in late winter through early spring in most nurseries, garden centers and mail-order companies. Many plant varieties are available bare root - fruit and shade trees, flowering shrubs, roses, grapes, cane fruits and strawberries.

One of the bare root selections for my yard
include these thornless blackberries,
which I planted in large barrel containers.

Among the benefits of bare-root plants are that they tend to cost significantly less, and establish quicker than their containerized counterparts. One of the reasons for their quicker establishment is that when you plant bare-root plants, you generally backfill the hole with soil that was dug from the hole. This means that the roots grow in only one type of soil. When you put a containerized plant in the ground, there are two types of soils - that from the container and that from the ground. This usually creates layers with a difference in textures coming in contact with each other. When this occurs, water doesn't penetrate the rooting area evenly.

When purchasing bare-root plants, look for plants with clean, evenly colored bark, strong stems, and firm, well-formed, healthy-looking roots. Avoid plants that have leafed out, unusual swellings other than the graft union, suspicious holes, and slimy or withered roots. Of course, seeing the roots may be impossible on plants with plastic wrappers on them. Keep your receipt and return the plant to the store if you find any of these root conditions once you have opened the package.

Bare-root plants should be planted as soon as possible after purchasing. If you must delay planting, temporarily plant them in a trench with potting soil or sand on the shady side of your house and keep the roots moist, but not soggy. Whatever you do, don't let the roots dry out. Before planting, make sure to remove and discard any saw dust/wood shavings that the plant may have been packaged in, soak the roots in water for 30 minutes to four hours, and then trim off any broken or damaged roots back to healthy tissue.

When planting bare root plants,
make a mound at the bottom of
the hole (in the ground or in containers),
spread the roots out around the mound,
and then backfill making sure
to not leave any air pockets.

When preparing the hole for bare-root plants, make a firm mound of soil in the bottom of the hole, and then spread the roots over the mound, which helps to eliminate air pockets at the center of the roots, and then position the plant to the same level it was in the growing field. Hold the plant upright as you backfill the soil, making sure to firm the soil as you go. When backfilling is almost done, adding water helps to settle the soil and eliminate air pockets. Finish filling the hole with soil, then water again. Water once or twice a week, but don't over-water while the plant is still dormant because soggy soil may inhibit new root growth, or cause existing roots to rot.

When the growing season begins, form a well from soil around the planting site. Water when the soil becomes dry at a depth of two inches.

My blackberry plant all planted in its container.

Another thing to consider when choosing bare-root, or any other fruit tree, is whether a pollinator is needed. In most cases, the label on the plant will tell you if the plant is self-pollinating/fertile or if it needs a pollinator. If it needs a pollinator, suggested varieties are usually on the label. If you have any doubts, ask a knowledgeable sales person. Common fruits that need pollinators include almonds, pears, apples, plums and cherries.