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GROWING FRUIT TREES PLUMS

 

Growing a Plum Tree

A plum is a sweet edible fruit produced by a plum tree (Prunus domestica). Plum trees are grown worldwide and have been cultivated by humans for thousands of years. There are hundreds varieties of plums, so it is important to choose one that is right for your area.

 

Type

Edible plums are usually divided into two groups: European and Japanese, for purposes of pollination. Additionally some varieties of plums are grown for fresh eating, while other varieties are grown for preserving or jam making.

 

Size

Grafted plum trees are all similar sizes that can be maintained at approximately 15’-17’ tall.


Pollination

Many plums are self-fertile and require no pollinator, however some varieties are not. Unless otherwise noted, Japanese plums with only pollinate with Japanese plums and European plums will only pollinate with European plums. While many plums are self-fertile, generally a pollination partner will increase the size and quality of the harvest.

Pollination is important during your orchard planning as well, since you need pollinators to fly between your plum trees. The pollinizers should be planted no further than 50 feet apart, to ensure proper cross-pollination.

 


USDA Hardiness Zone

Plum trees are hardy to USDA zones 4-9, unless otherwise noted . This rating tells you the minimum winter temperature the plants typically survive when properly hardened off. On our web site you will find a USDA Hardiness Maps  which provides information on the average minimum winter temperature in your location, by zip code.

 


Chill Hours

Plums need a certain number of chill hours per year, which means that you need to pair the chill hours to your climate. If you live in the south or an especially temperate area, you will want to choose a variety of plum classified as “low-chill”. This means they have a lower required amount of hours the temperature is below 45F degrees.

 


 

Where to Plant Your Tree

Plums need to be planted where they receive at least 8 hours of full sunlight. People often don’t realize that it is the sun that ripens the fruit, and without enough of it your plums will never fully mature.

Plum trees like well-drained soil, nothing too wet. Soil can be somewhat rocky and sandy, but needs to be moderately rich and retain moisture as well as air. Clay soil should be amended prior to planting, but can be accomplished by mixing in coco-coir and perlite to improve drainage.

 


 

Growing in Containers

Plum trees generally grow too large to successfully grow in a container.

 


 

Care and Maintenance

Watering Your Tree

This is the most important and often the most difficult part of successfully growing plants. There are many factors, including the humidity, temperature, soil type, wind, and amount of direct sun that affect how much and how often water should be applied.

A general rule of thumb for plants in the ground is to ensure they receive an inch of water per week over the root zone. An inch of water is equivalent to about ¾ to one gallon per square foot of soil surface area. The typical three foot diameter planting hole would need 7 ½ to 10 gallons of water per week provided by rainfall or by the gardener.

Apply this water once a week, two times per week if soil is fast draining. This will of course depend on your own conditions and the plants you are growing! DO NOT water lightly each day because this results in a wet surface and dry root zone area. The soil should be moist but not soggy to a depth of about a foot for most growing plants. The top inch or two can feel dry, and the plant still be well watered. The trick is to have the water available where the roots are. In hotter and sunnier areas, a mulch of straw, bark, etc. can greatly ease the burden of summer watering. For plants in containers, water until the soil is saturated and water comes out of the drainage holes. Let the container dry until the soil is dry to the touch 1-2 inches down and the container is lighter in weight. A plant that has wilted can be receiving either too much or too little water.

In rainy areas like the Pacific Northwest most of the plants that we offer will need relatively little supplemental irrigation ONCE THEY ARE WELL ESTABLISHED in the ground and have had a chance to develop a good root system. However even here it is important to make sure plants have regular, deep watering during the first couple of growing seasons, and the first summer is especially critical. In drier areas, permanent irrigation is essential. Remember that you don’t want your trees to just survive, but rather to thrive. Make sure they get the water they need.

One method is through drip irrigation. We use half- inch flexible plastic pipe with punch-in emitters for trees in the ground. For each young tree, we use two emitters, spaced one foot from the trunk. The pipe can be put on the ground, under the ground with risers, or tied loosely from the trees. We use emitters that drip one gallon per hour. See drawing above. There are many different styles of drip systems, some controlled by timers and others by hand. Or, each tree can be watered with a hose deeply about once a week. Sandy soils will need more frequent watering than clay soils. For smaller plants, like strawberries or raspberries, soaker hoses work very well.

 

Fertilization

For good steady growth and high productivity, your trees need to have adequate amounts of various mineral nutrients. Some people are fortunate and have naturally rich fertile soil. Many soils, however, are deficient in some nutrient or another and use of fertilizers, organic or chemical, can be highly beneficial if you want your trees to grow well. If you have a large gardener orchardist can be well worth it to have your soil analyzed by a qualified laboratory so you know for sure just what your soil needs. Typically this might cost $30-$60, depending on how detailed an analysis you want. Unless you know what is available in your soil, you will not be able to supplement it properly.

Use an all-purpose or balanced fertilizer like the organic fruit tree and shrub fertilizer.  A couple of inches of well-rotted compost on the root zone can also be ineffective fertilizer. A generous leaf or straw mulch around your trees will not only conserve moisture and help in weed control, but also keeps your soil healthy by building up humus, attracting earthworms, and supporting beneficial fungal organisms. This encourages young trees to be strong, healthy and productive. Use of concentrated products like chemical fertilizers or strong organics (for instance blood meal) is usually done from late winter through early summer. Applying fertilizer after early summer can encourage lots of soft new growth that is much more likely to be damaged by winter cold. Excessive use of fertilizer can in-crease disease problems on your plants and can even kill them. Use of too much fertilizer, whether chemical or organic, canals contribute to stream and groundwater pollution, so please try not to use more than your trees really need. As a general guide, if your tree is producing about one foot of new growth or more a year and has healthy looking foliage, it may not need much or any fertilizer.

 


 

Pests and Diseases

 

Bacterial Canker

Symptoms

Sunken blackish cankers on stems or trunk, wilting and death of branches, gummy ooze from cankers, dead dormant buds.

Control Methods

Copper fungicide in early fall and again in January. Cauterize cankers with a torch in early summer. Apply foliar micronutrients to aid tree immune system.

Comments

This disease is most severe when spring frosts damage bark or when pruning is done in winter or early spring before bud break. Newly planted trees are especially susceptible.

 

 

Brown Rot

Symptoms

Wilting and death of twigs and blossoms. Fruits turn rotten, gray-brown in color, often hanging from the tree as “mummies”.

Control Methods

Promptly remove any infected twigs or mummified fruits. Apply copper, sulfur, or lime-sulfur fungicide at petal fall, midsummer, and again in fall.

Comments

Blossom brown rot can be a difficult problem in very wet spring seasons. Spray promptly as soon as dry weather permits.

 

 

Peach Leaf Curl

Symptoms

New leaves blister, deform, turn reddish, and eventually die.

Control Methods

Plant resistant varieties. Lime and sulfur applied starting in mid-December. Spray are 3-4 week intervals.

Comments

Prevent infection by covering the trees from December to February to keep stems dry. Control times vary with climate. For low-chill varieties, apply spray 3-4 weeks earlier.

 

 

Cherry Slug

Symptoms

Dark olive green slug like larvae skeletonize leaves, especially common in summer

Control Methods

Insecticidal soap spinosad, pyrethrin, rotenone dust, or bioneem. Pick off and destroy by hand.

 

Comments

Trees can tolerate up to 25% defoliation with little harm. Not actually a slug; just resembles a slug. Also affects pear, plum, hawthorn, and mountain ash.

 

 

Shot Hole Disease/Corynium Blight

Symptoms

Small reddish-purple spots on leaves, which fall out leaving holes. Fruits may also be spot ted. On peaches, twigs may also be spotted and develop cankers.

 

Control Methods

Bordeaux mix or copper fungicides in early fall, winter, and spring.

 

Comments

Spores are spread primarily by splashing water, keep sprinkler water off foliage and fruit.

 

Scale

Symptoms                                   

Small barnacle-like bumps on branches and leaves.

 

Control Methods

Dormant oil spray in early spring.

 

Comments

Insecticidal soap or soap/oil spray during juvenile phase.

 

 

Deer

Symptoms

Browsed shortened branches. Leaves are obviously munched on or plants are pulled up.

 

Control Methods

Fences or cages at least 8’ tall. Plastic mesh, electric, or woven wire fences.

 

Comments

At Raintree, an 8’ woven wire deer fence has worked best. Repellents don’t work consistently. and only trained large dogs patrolling the perimeter are effective.

 

 

Bird

Symptoms

Fruits disappear or have gaping holes in them. Strawberries, blueberries, cherries and filberts are most susceptible but most fruits suffer occasionally.

 

Control Methods

Reflective Bird Scare Tape can work well. Bird netting. Cages.

 

Comments

Blue Jays start harvesting filberts when ready to pick, and so should you. Nuts dropped by jays are usually empty.

 

 

Vole/Mouse/Rabbit

Symptoms

Bark eaten in a band from soil level up to 8” and roots eaten too, usually in snowy areas with lots of mulch or tall grass at base of trees.

 

Control Methods

Keep mulch 4”-6” away from trunk. Keep grass short and 1’-2’ from trunk. Use vinyl tree guard wrapped around trunk until tree well-established.

 

Comments

Voles and mice will chew a couple inches above ground and also into the root system. Rabbits will chew up to 8” high, particularly apple trees.


 

Aphid

Symptoms

1/32 to 1/8” long pear shaped insects that multiply rapidly, espe- cially on the underside of leaves and on stems. Can be pink, green, black or white. Leaves show red blisters or are curled-down and stems turn black with sooty mold.

 

Control Methods

Natural predators like lady bugs and parasitic wasps often provide control. Knock aphids off with water spray. Spray with Pyrethrin, Rotenone, Insecticidal Soap, or delayed dormant oil. Control ants if they are also present.

 

Comments

Trees can tolerate some infestation. Monitor in late spring and summer. Control is more important on new trees. Grow plants that attract predators, i.e. dill or yarrow.

 

 

Ant

Symptoms

Numerous ants scurrying up and down the tree trunk; aphids, scale or mealybug present in large numbers, lots of sticky honeydew, perhaps sooty mold.

 

Control Methods

Find hill and apply pesticide. Apply Tangle Trap over 2-3” wide band of paper wrapped around trunk. Eliminate other pathways into tree.

 

Comments

Ants nurture and protect these insects in exchange for their sugary secretions. Insects may be difficult to control until the ants are controlled.

 

Brown Marmorated Stink Bug

Symptoms

Poking-type feeding damage followed by decay on fruits, nuts, berries and leaves. Deformity in the healthy tissue surrounding the dead tissue. Brown spots can show up in stored fruit.

 

Control Methods

Monitor with traps, some broad spectrum pesticides may work. Researchers are working on finding effective controls, but no info has been released yet.

 

Comments

BMSB over winters in groups in dry protected areas, such as houses. If you find them on or in your home use the vacuum, squishing releases their defensive stink.  See stopbmsb.org for more info. Feeding begins in spring when the weather warms up and continues until new adults go dormant for winter.

 

Rust

Symptoms

Lesions on the upper surface of the leaf, or on the fruit or stems, followed by orangish structures on the bottom side of the leaf, or on the fruit or stems, which produce spores.

 

Control Methods

Copper fungicide after harvest before fall rains and again in early spring for prevention of some\ rusts. Remove and destroy infected parts of the plant. If possible select resistant varieties. Many varieties have not been studied. Cedar-apple rust is a problem east of the Rockies.

 

Comments

Rust diseases require an alternate host, removing the host (within 900’ radius), applying fungicides, or removing infected parts may help. Check with your extension office to see what rust diseases in fruiting plants may be common in your area, and their alternate host.

 

Sunscald

Symptoms

Vertical splits in bark appear spring or early summer, usually on the south or east side of the tree. Disease or insect infestations may then occur.

 

Control Methods

Whitewash trunk and lower limbs with interior latex paint cut 50/50 with water each fall until bark has thickened. Avoid planting in frost pockets or where water collects in winter.

 

Comments

Injury occurs during pattern of warm days followed by freezing nights. Sap gets stuck in trunk, freezes, then rapidly thaws in the warm sun the next day, rupturing cells.