Tough, Versatile Junipers

 If you’re looking for a tough plant to grow somewhere in your landscape in a place where most others fear to tread, a juniper may be just the thing. These hardy, drought tolerance evergreens are available in more than 170 varieties, ranging from low-growing shrubs to tall, slender trees. Foliage color can vary from light to dark green, blue to silver and yellow to gold. Low-growing varieties make excellent groundcover or foundation plants while the taller-growing types are well suited for screens, hedges or windbreaks. All in all, they are truly work horses in the landscape.

Planting

Junipers are very tolerance to adverse conditions including drought, heat, a wide range of pH levels, dry, clay soils and sand. But they do have two essential requirements—full sun and good drainage.  

Proper spacing is also important because when planted too close together, lack of air circulation at maturity will make them more vulnerable to insects and disease.

Prepare their permanent home by first digging a hole two to three times wider than the size of the root ball and no deeper than its depth.  Remove the plant from its container and break up the root ball with a knife or your hands. Most of the bark the plant was growing in will come off so mix it in with the backfill soil. Then place the top of the root ball level with the soil surface. Fill in the backfill soil and tamp down to eliminate air pockets. Water thoroughly after planting and keep it watered in the absence of rain. Water amounts depend on the time of year, but if you plant during the dormant months of November or December, you may not have to water again until spring or summer.

Fertilization and Watering

Once established, junipers need very little if any supplemental irrigation. They are one of the most drought tolerant plants in our landscapes and can actually suffer from over watering. However, if they have been accustomed to regular irrigation for many years, they can suffer if the water is suddenly and permanently eliminated.

Junipers respond well to a balanced fertilizer such as two teaspoons of 10-10-10 per one-gallon plant at planting. Incorporate the fertilizer into the soil or spread it around the plant, but avoid directly placing fertilizer into the planting hole unless it is a slow release type such as Osmocote.

Established junipers will benefit from a complete fertilizer such as 16-4-8 applied at a rate of one-half pound per 100 square feet in early spring and again in late summer. If you have older or mature junipers, fertilizing once during spring should be enough.

Pruning

Junipers do not tolerate heavy pruning because of the lack of new growth on old wood. Therefore it’s important to know the growth habit of a particular juniper prior to planting so that future pruning can be minimized. Junipers can be tip pruned and thinned, but not cut back to large limbs where there is no foliage. Pruning out old, dead foliage underneath creeping junipers will often contribute to better air circulation and thus better health of the plant.

Pest Problems

Although junipers are tough, they can fall prey to common insect pests including bagworms, spider mites, leaf minor, webworm, scale and aphids, all of which can be controlled (some better than others) with an appropriate insecticide. The following is a guide to identifying and treating junipers for these common insects.

Spider Mites.
Spider mites are the most serious pests of junipers. They are small and not easy to see with the naked eye. They have piercing mouthparts to suck plant sap, which results in speckling on needles. When bad enough, needles may turn brown and fall off. With heavy infestations, fine webbing may be seen on the plant. Several seasons of heavy untreated mite feeding can kill a juniper.

Control.
Naturally occurring enemies of mites include other predator mites, ladybugs and other insects. These predators will usually suppress mite populations. Since insecticide use kills beneficial predators as well as mites, use insecticides as a last resort. Unfortunately, there are basically no good miticides on the market for homeowners. Of those available the best insecticides are: acephate (Bonide Systemic Insect Control), bifenthrin (Ortho Max Bug-B-Gon) and disulfoton (Di-Syston, Bayer Advanced  2 in 1 Systemic Rose and Flower Care). Organic alternatives include horticultural oils, insecticidal soaps and sulfur. Mites don’t like water, so many can be removed with a strong spray of water, if applied regularly.  

To determine whether a mite infestation is severe enough to warrant insecticides,  hold a white sheet of paper under a branch and shake the branch. The mites that are knocked off will be seen crawling around on the paper. You may need a magnifying glass to help you see the mites.

Bagworms.
Bagworms infest many shrubs and trees, but conifers (evergreens) are the preferred hosts. Caterpillar feeding causes plant damage, which causes loss of foliage. Mild infestations slow the growth of junipers, while heavy infestations can kill a plant.

Prevention and Control.
Several parasites and predators feed on bagworms, generally keeping their numbers under control. Removal of the egg-containing bags during winter and early spring is a very effective method for preventing problems before next growing season. Once removed, destroy the bags.

If the infestation is severe or the bags are out of reach, spray with the organic bacterial insecticide Bt (Thuricide). This insecticide contains spores of the bacterium, Bacillus thuringiensis, which when eaten kill the caterpillars. Young larvae are much easier to kill than are older larvae so apply in the spring as soon as bagworms are seen. Control is most effective when spraying is done in late afternoon or early evening. Other insecticides that provide good control are malathion and various pyrethroids such as bifenthrin (Ortho), cyfluthrin (Bayer Advanced) and lambda cyhalothrin (Spectracide).

Diseases

Several diseases can occur on junipers, but are almost always associated with poor cultural problems such as overwatering, overly wet soils and too much shade.

Twig and Tip Blight.
Junipers frequently exhibit die back of shoot tips or entire shoots and browning of needles. Needles may drop from the plant and dark cankers may form at the junction of live and dead wood. This problem typically occurs during warm, wet weather conditions and is usually caused by one of the fungal organisms described below.

Phomopsis Tip Blight.
This disease begins by infecting the tips of branches smaller than the diameter of a pencil. The new, immature growth becomes infected while the darker green, mature foliage remains resistant to infection. Infected twigs become pale, then turn reddish brown and finally become brown after death. Scraping away the bark will reveal a sharp line between discolored, dead wood, and healthy wood. Watch for disease development during the spring or summer flush of new growth when warm, wet conditions are present.

Kabatina Twig Blight.
Symptoms are the same as described for Phomopsis tip blight, except this fungus kills older twigs in the spring. Damaged or stressed tissues are more susceptible to Kabatina twig blight.

Cercospora Twig Blight.
Begins by infecting the oldest needles that are located on the lower branches, inside the plant. As disease development progresses, the needle browning spreads upward and outward. Branch tips usually remain healthy and green. Needles of spur branches turn brown and die usually in the late summer, leaving a plant with an inner crown devoid of foliage. This disease is sometimes confused with mite damage.

Prevention and Treatment.
Each of these diseases requires similar methods of control. First, closely inspect the entire plant, since symptoms of tip and twig blight can be caused by other problems, such as drought, overwatering or root injury.

Purchase disease-resistant plants that are healthy with no evidence of dead or dying twigs. Don’t plant them in shaded or poorly drained locations and select areas with good air circulation to promote rapid drying of needles. Do not crowd plants and avoid frequent overhead irrigation. Promptly prune and remove any diseased or browning branches as they occur. Except on highly susceptible cultivars, pruning will usually control these diseases.

If chemical control is necessary, fungicides are available for protection, but they must be applied before infection occurs. Select a fungicide labeled for use on junipers containing one of the following: mancozeb (Bonide Mancozeb Flowable, Dragon Mancozeb Disease Control), thiophanate-methyl (Fertilome Halt Systemic Rose and Flower Fungicide, Green Light Systemic Fungicide) or copper compounds (Bonide Liquid Copper, Dragon Copper Fungicide, Hi-Yield Copper Fungicide).

Phytophthora Root Rot.
This is the most serious and difficult to control fungal disease that affects not only junipers, but a wide range of plants in area landscapes. It is caused by a soil-borne fungus and the most common symptom is the slow decline of the plant. Leaves on the plant become thin or sparse. Some plants may die a branch at a time.The centers of the roots change from white to reddish-brown and the outer layer of the roots separates easily from the core. High soil moisture and warm soil temperatures favor disease development.

Prevention and Treatment. 
It is important to prevent this disease by cultural methods, since chemical treatment is ineffective once symptoms appear. Avoid planting in poorly drained areas where this root rot thrives. Heavy clay soils, areas that flood and sites where runoff water is a problem typically create root rot. Plant junipers in raised beds, except in deep sandy soils.

Avoid varieties that are the most susceptible to rot. Junipers  likely to be killed by root fungus include Andorra, Bar Harbor, Parsoni, Sargents, Shore and Juniperus procumbens Nana.

Soil-drench fungicides, such as Banrot and Subdue, can be effective on a preventative basis and require repeat applications. They will not cure an infected plant. There are no “homeowner” fungicide soil drenches, as they are only packaged for commercial applicators. You don’t need a pesticide license to buy them, but they come packaged in containers that make private purchase and use impractical. Homeowners may want to hire a landscaper to apply these products.