Growing mulberry trees

Every gardener struggles with weed control, but please be aware of the personal health effects and environmental concerns of using herbicides. Although not readily available to the home gardener, one product that appears to be much more toxic than most others is paraquat. Here is a link to the dangers of paraquat: https://www.drugwatch.com/paraquat/
At the request of another consumer protection organization (consumernotice.org), I've been asked to post this link to information on the dangers of glyphosate. My long-time best friend (who never smoked) is in Hospice care dying of lung, kidney, and brain cancer, which in my opinion, originated from the constant spraying of glyphosate in his orange grove over the span of many years, without using a respirator. https://www.consumernotice.org/environmental/pesticides/roundup/

Site Selection and Preparation

The first consideration when planting mulberries is to choose a location away from driveways and walkways, where the berries and bird droppings pose a hazard. Do not plant mulberry trees near septic systems, as they have invasive roots. Consideration of their mature size also needs to be addressed; unless you are planting a dwarf variety, most mulberry trees will attain a height exceeding 30 feet tall and equally as wide. Properly pruned, they can be a delight to relax in their shade on a warm summer day, as they have a pronounced cooling effect. Mulberries will fruit heaviest in proportion to the amount of sunlight received, but if a heavy load of fruit is not your main concern, most mulberry varieties grow reasonably well under almost any sunlight condition, short of complete shade.

For optimum growth, the soil where you are planning to plant your mulberry should be well-drained and between pH 5.5 and pH 7.0. If the soil is below pH 5.5, it can be limed. Soil with a pH between 7.0 and pH 8.3 can be treated with sulfur to lower the soil pH. Although not ideal, Morus rubra and Morus nigra can grow in soils up to pH 8.5. Your county agricultural extension office can accurately test your soil for pH and nutrients (some even do testing for free), or you can get a soil test kit from a home improvement center for under twenty dollars. Ideally, soil treatment should be done at least a year before planting, but few have that kind of foresight.

If the planting location is not a rich organic loam, you should add a good amount of organic matter to the planting hole, as this will greatly enhance the growth of your tree and protect the roots from becoming too dry during droughts. One or two bags of compost (from a nursery, home improvement center, or your own mature compost) should be mixed in at a ratio of 1 part compost to 3 parts soil from the planting hole.

A simple test to determine if your soil is in the proper pH range for growing mulberries: Take two “zip-lock” quart bags and put a quarter cup of your soil in each bag. Mark one bag “acidic test” and the other “alkaline test”. Put a tablespoon of baking soda (sodium bicarbonate) into the bag labeled “acid test” and mix well. Add water to cover soil, and while expelling the air out of the bag, immediately seal. Put aside. In the bag labeled “alkaline test”, add one-quarter cup of white vinegar and seal as before. Look at the two bags. If the “acidic test” bag has a lot of bubbles or foam, your soil is acidic and could benefit from liming. If the bag labeled “alkaline test” has a lot of bubbles or foam, your soil is alkaline and could benefit from the addition of sulfur. If you don't see little white bubbles in either bag, check them again in an hour. If both bags show no signs of bubbles and have not puffed out at all, your soil is most likely in a good pH range for mulberries.

Planting

The planting hole should be at least three feet across and deep enough to accommodate the roots without bending. Remove your mulberry plant from its container and if it is slightly root-bound, place it horizontally on the ground and, using your fingers, loosen up the roots (at the outer surface only). If it is heavily root-bound, using a hand pruner, make 3 to 5 cuts down the sides and across the bottom, cutting through the mat of roots to a depth of about an inch (This is extremely important: Root-bound plants will stifle and suffocate their own growth if planted in the root-bound mode). With a helper holding the plant in the planting hole at the same level it was growing in the pot, start filling the planting hole with the soil/compost mixture; breaking a few times to water in well. Staking your plant is a good idea to prevent it from being uprooted by wind or varmints.

For bare-rooted trees planted in the dormant winter season (mail-order plants are often shipped this way), plant in the same way as specified above for the container-grown plant, but put extra emphasis on keeping the plant well watered until established.

After Planting

If the plant is dormant and without leaves, it is only necessary to water infrequently when the soil starts to become dry. When growth returns in the spring, keep it well-watered. A ten dollar soil moisture meter works quite well to assist in knowing when and how much to water. After their first year, mulberries can withstand more infrequent watering. Established trees seldom die in drought periods, but water-stressed trees will drop their fruit (a moist soil is also needed for good fruit set).

If available, mulberries enjoy a 4” to 6” blanket of leaves or mulch extending at least 3 feet from the trunk (but not touching the trunk). Mulching keeps the roots near the surface moist and cool while inhibiting weeds which rob the tree of nutrients. Fertilize with two cups (10-10-10 or equivalent amount) of fertilizer containing minor elements when leaves begin to appear in the spring (but at least four weeks after planting). Fertilize again early summer; if your soil is fairly fertile, a light application every spring may be all that is necessary to produce abundant crops of berries. Mulberries do very well with organic fertilizers or composted manures.

Young trees are also much more susceptible to harsh winter conditions. So often it is reported a young mulberry tree failed to break bud in the spring. Young mulberry plants do not have thick bark and a deep root system, nor do they acclimate well to an approaching winter. If a hard freeze is in the forecast while the young mulberry still has green leaves it may be wise to give it some protection. It should also be protected during extremely cold winter events. An easy practice is to mound mulch to protect the young tree. If winter conditions become too severe for the branches above the mulch, at least you will have a live plant in the spring (make sure your mound of mulch stays well above the graft union). Carefully remove the mulch in spring before bud break.

Mulberry leaves contain up to 17% protein (dry weight) which makes them very desirable to deer. Deer have a voracious appetite when it comes to mulberries and in one night may not only strip all the leaves off of your young mulberry plants but may also eat the stems all the way to ground level. If there are any deer in your area it is best to be proactive and protect your young plants before a tragedy occurs. Repellants made specifically for deer work to a limited extent, but by far the best protection is achieved with a cylinder of 5' high field fence around each young plant. Use at least two posts to prevent deer from knocking the wire cylinder over. Besides eating the tender parts of young mulberry plants, rutting deer will also rub off the bark of mulberry trees; If the bark is removed completely around the circumference of the tree it will die. A variety of materials, from fencing to corrugated drain pipe (split open with a box knife or jigsaw) can provide a barrier to prevent this from happening. Protecting the truck to 4' high is recommended.

Training

Mulberries generally need very little pruning to grow into an attractively shaped tree (if their ornamental value is your main concern). Morus albas are especially prone, though, to branches that overlap each other, and some authorities feel those branches should be removed. Because of mulberries' tendency to bleed a white sap when cut, it is recommended to save major pruning jobs for the winter months, “when the sap is down”. Mulberries grow rapidly, and soon that little stick you planted can turn into a towering monster, leaving just a few lower branches reachable for berry harvest. This is where it becomes advisable to prune the tree so most of the fruit remain accessible. Pruning out the center branches growing upright, opening up the center of the tree, and encouraging lateral growth, will keep the majority of the harvest within reach. Opening up the center allows the lateral branches to receive more sunlight and increase the yield on those branches. Pruning doesn't usually affect production since most mulberries produce fruit on new growth. Unfortunately, "pure" Red Mulberry (Morus rubra) cannot be heavily pruned. Active buds are generally only found near the terminal ends of branches, while the base of the branches lack the specific meristematic tissue which would give it the ability to differentiate into new growth from dormant buds. Most Red Mulberry cultivars are actually hybrids with White Mulberry and will do quite well with light pruning.

Branches can also be made accessible by pulling down their tips until almost touching the ground and then releasing, thereby reshaping the tree (A safer approach is to tie string to the tips and fasten to bricks for a week or so).

Mulberries can be forced into growing into a bush form. Wait until the trunk on your mulberry tree is at least 1" in diameter at the base and cut it off at ground level (Note: This only works on mulberries that are not grafted, unless the grafted plant had originally been planted at least a foot below the graft union for more than a year). Multiple shoots should spring up from the base and it should grow into a multi-stemmed bush. I have only done this a few times, so attempt this at your own risk, since I have no idea if most cultivars will reliably adapt to a bush-like form.

Pruning can also be used as a tool to induce fruiting. In areas of the country lacking sufficient cold weather for certain cultivars, heavy pruning can be used to stimulate fruit production. It may be necessary to remove one third to one half of the plant to be effective.

As to their hardiness, a Carolina mulberry grower testified as follows: "Yeh can't kill the things. Yeh kin plant yeh mulberries jest like yeh would cane—cut it off in joints and graft from the one yeh want to. I moved a tree last yeah. Jest put a man cuttin' roots off— and he cut 'em scandalous—and I hooked two mules to it and hauled it ovah heah.

I didn't 'spect it would live, but it did."

"A Georgia Tree Farmer"; J. Russell Smith, The Country Gentleman, December 4, 1915, pp. 1921-22.

Insect Pests

Insect infestation can affect the beauty and charm of a mulberry tree, but seldom pose a serious problem for obtaining good fruit production. If you learn that certain fruit-loving insects are a problem in your area, most varieties of Morus alba have an early fruiting period which occurs before most insects “wake up” from winter dormancy. Since ants are in a symbiotic relationship with certain insects, “Tanglefoot” applied to the tree trunk (please refer to instructions) to stop the movement of ants can go a long way to limit insects such as scale, mealybugs, and aphids.

Fall Webworm

Scale

Thrips

Fruit fly

This common caterpillar can defoliate large sections of a tree. Prune out the branches containing their nests of webbing, if so desired. Better yet, open their nests with a stick to give birds a treat.

Whiteflies make their presence known by flying up from lower leaf surfaces in a cloud of white when a branch is disturbed. Their sweet excretions cause the growth of sooty mold. Infestations seldom become a serious problem and control is not recommended.

Whiteflies

Various scale insects can infect the trees, feeding off their milky sap. "White Peach scale" can severly weaken plants. Two dormant oil sprays applied before spring can reduce infestations.

White cotton-like masses on shoots and twigs indicate Mealybugs. A large infestation can hurt tree growth and vigor. Removing infected twigs and Neem oil sprays help to control their numbers.

Mealybugs

Various species of these minute sucking insects can cause significant leaf or fruit damage. Leaves display a silvery dappled appearance, while other species cause fruit to become dried and shriveled. Neem oil (for leaves) or Spinosad may offer some control.

See Below

Stink bugs are attracted to MOST fruit trees and mulberries are no exception. These crafty, juice-sucking insects are always on the look-out for predators, so disposing of them can be challenging.

Stink Bug

Fruit flies can be a problem in some parts of the country. Not affecting tree health, their larva can develop inside fruit and make it less desirable (but still edible). Over-ripe and damaged fruit are the most susceptible. See the section on “Harvesting fruit” to remove these and other insects from your fruit.

See Below

Leafroller larvae (caterpillars) can cause severe defoliation in some years. The moth responsible does not seem to discriminate between mulberry plants and no cultivar appears immune to infestation. The larva protects itself from predators by using its silk to pull sections of leaf into a tunnel. Bacillus thuringiensis sprays are a safe, effective control.

Leafroller

Thrips and fruit flies can cause significant damage to fruit and most people consider them unappetizing. Thrips tend to be abundant during dry weather, while fruit flies are usually most abundant in wet weather. If you notice tiny insects flushing to the surface of the fruit and scurrying about when it is bent, they are most likely one of many species of thrip. Fruit flies on the other hand tend to hover around the fruit when disturbed.

An effective control for thrips (and I've tried them all) is just a simple vegetable oil spray. Most searches and videos will state one or two tablespoons of oil (olive, soy, canola, etc.) but in my experience, it is necessary to use up to four tablespoons of oil per quart. Also, add a tablespoon of dish detergent. The mixture MUST be continuously shaken while it is being sprayed on the fruit because the oil separates from the water. Spray should be directed at the fruit, avoiding the leaves as much as possible...especially when the weather is forecast to rise above 85 degrees F. In periods of heavy infestations, it may be necessary to spray every three days. If your infestation of thrips is extremely heavy, or you have a fruit fly infestation, a tablespoon of Spinosad can be substituted for one of the tablespoons of oil. Spinosad alone is not very effective in controlling the insect pests on fruit, the addition of oil is the key. Although Spinosad has an extremely low toxicity profile to mammals, rinse fruit well before consuming. For those that wish to avoid any pesticide for fruit fly control, a tablespoon of peppermint oil, substituted for one of the tablespoons of vegetable oil, appears to repel some species of fruit flies.

Ants can be a serious nuisance, but are easily controlled by a barrier of a sticky, grease-like product called "Tanglefoot". It is a petroleum product, so it cannot be applied directly to the trunk, since it can kill a young tree. Cover about 3 or 4 inches of the truck with "flagging tape" and apply a thick layer of "Tangefoot" to the tape. Apply the tape and product as high as practical, so it doesn't pick up leaves or grass clippings during mowing.

Diseases

Bacterial and Fungal Leaf Spot are the two main diseases that affect mulberries. Both are spread by rain and wind. Raking up fall leaves under the tree may help delay the onset of fungal leaf spot, but control is difficult or impossible if conditions become favorable for development. Fungal Leaf Spot is more pronounced on older leaves and often results in premature leaf drop. Affecting the vigor and beauty of the tree, it seldom seriously affects fruit production.

Bacterial Leaf Spot is a more serious disease and causes dieback of new growth and stunting of growth in general. Progression of the disease can be minimized by pruning off the affected growth during the winter, but it cannot be eliminated.

The best control measures for these two diseases, especially in locations with warm, wet, and humid springs and summers, is to plant cultivars that are more resistant to these diseases. Morus macroura cultivars and hybrids do exceptionally well, as do Morus rubra cultivars and hybrids. Shangri-la is a Morus hybrid that originated in Naples, Florida that is supposedly disease-resistant (it probably is a Morus rubra or macroura hybrid).

Popcorn disease (from Mississippi State University Extension)

"Popcorn disease of mulberry is caused by a fungus (Ciboria carunculoides). It occurs in late spring and early summer. The white mulberries are more susceptible to this disease. The disease manifests on the developing carpels and looks like popcorn kernels. It is a serious disease if the tree is being cropped for commercial purposes; however, it does no harm to the overall health of the trees, thus homeowners do not need to worry (if the tree is only used for ornamental or shade purposes)."

"So, if this disease does occur what can be done to stop it? Sanitation is a good first step — clean up any infected material and remove it from the area where the tree is growing. There is very little else a homeowner can feasibly do to reduce the disease. Spraying the tree with Bordeaux mixture may help too, but getting coverage over the entire tree may be problematic. As with many fungal diseases, the severity will depend on the environmental conditions from year to year. Some years will be worse than others."

Fungal Leaf Spot

Popcorn disease

Fusarium canker

Fusarium canker is caused by several different species of Fusarium fungi. It produces lesions, which are usually elongated, in the bark of branches or the main trunk of the mulberry plant. The canker disrupts the flow of nutrients, resulting in die-back of the branch above the canker. Cutting through the branch at the site of the lesion will reveal dark discoloration in the wood.

There is no effective chemical treatment for Fusarium canker. It is controlled by cutting the affected branch at least 3 inches below the infection. The removed branches should be burned or hauled away. Disinfect your pruning tools (before and after) with 10 percent bleach or 70% isopropyl alcohol. It may be a good practice to spray the cut with a fungicide also.