A plum is a sweet, edible stone fruit produced by a plum tree (Prunus sp.). Plum trees are grown worldwide, including the United States, Western Europe, Eastern Europe, the Middle East, Japan, and China.
Plums come from a variety of places. Prunus domestica are native to Eastern Europe and the Caucasian mountains, while Prunus salicina originated in China. In recent years a number of improved varieties and hybrids have also entered the world of plums.
Centuries of cultivation and selection have given us a wide variety of plum fruits, both large and small. Different plum tree varieties have different pollination requirements; the fruits have a wide range of textures and uses in your kitchen including fresh eating, jam making, drying, baking, sauces, salsas, chutneys, vinegars, and making alcoholic beverages. Below is a brief list of the different types of plums trees you can plant and cultivate in your own orchard.
So exactly what is a European plum? What does it look like and how does it taste? European plum trees produce plums with skins in a wide variety of colors – generally purple or yellow, although popular ‘Green Gage’ and Persian plums are often green. Many European plums are freestone and less juicy than Asian plums and are often canned, dried, or made into jams or chutneys. European plum flavor varies from intensely sweet to complex and floral, with different kinds of plums developed for different uses.
The main characteristic of the Damson is its distinctive intense flavor. Unlike many other European plums, Damson plums are both very high in sugar AND astringent compounds that give Damson its unique and complex flavor. Despite being clingstone, Damson plums are almost exclusively cultivated to create the most rich and wonderful plum jams. The trees are very reliable producers of heavy loads of fruit.
Prune plums are characterized by their high sugar content and low moisture content, creating a fruit that dries quickly and stores for long periods without refrigeration. Different kinds of prune plums originate from various parts of China, the Middle East, and Europe, with French and Italian prunes being the most commonly known.
Mirabelle plums are a special kind of European plum that is both smaller and more intensely flavored than many classic culinary plums. Despite being smaller than most plums, Mirabelle plums are exceptionally easy to pit and process, with an incredible floral flavor that has caused them to be one of the most sought-after fruits grown in France.
So exactly what is an Asian plum? What does it look like and how does it taste? Generally Asian plum trees produce plums with thin, tart skins in a variety of colors and shapes. Usually red, purple, or yellow and round or oblong, Asian plums are much juicier than many European plums. These qualities make Asian plums very popular for fresh eating and making salsas, vinegar, sauces and wine, but not as useful for standard cooking applications.
In recent years plum hybrids have become extremely popular for their intense and unique sweet flavors and novel skin colorations. Plum hybrids include pluots, pluerries, plumcots, apriums, and nectaplums. Complex crosses have some specific pollination and growing requirements, but they are definitely worth the extra time and effort to grow. They are reliably pollinated by Asian plums that produce a lot of pollen, like Shiro, Toka, Beauty, and Santa Rosa.
Size in both European and Asian plum trees is dictated by the rootstock they are grafted onto. We generally use two rootstocks, Marianna 2624 and St. Julian A. Both will produce a semi-dwarf sized tree between 10'- 15' feet tall, with some minor differences.
Marianna 2646 produces a larger semi-dwarf tree (80% of vigor) that can be easily maintained from 12 to 17 feet tall at maturity through regular pruning. This rootstock tolerates wet soils and has good disease resistance; it's moderately resistant to phytophthora, crown rot, root rot, and oak root fungus, as well as root-knot nematode resistant. Marianna 2624 can sucker in adverse conditions. Hardy to USDA zone 4-10.
St. Julian A produces a mid-sized semi-dwarf tree (75% of vigor) that can be easily maintained from 10 to 15 feet tall at maturity through regular pruning. This rootstock tolerates a variety of soil conditions including wet and heavy clay. St. Julian A is particularly good for colder environments with fluctuating early spring temperatures. Hardy to USDA zone 3-9.
Plum pollination is achieved primarily through pollinating insects. Self-fertile plum varieties provide self-compatible pollen to produce fruit and will openly pollenate other plum trees flowering at the same time, including those of the same variety. Plums varieties that are not self-fertile will require another variety of plum flowering at the same time to cross-pollinate. Below is a handy reference for plum pollination.
In general plums are considered a summertime fruit, ripening anywhere from 140-170 days from the end of the bloom period. Asian plums usually ripen earliest in the season, followed by complex cross varieties, and then European plums - some of which will continue ripening into the beginning of fall.
Unless otherwise listed, plum trees are hardy to USDA zones 4-9, making it possible to grow them all over the United States. The USDA zone rating tells you the minimum winter temperature at which the plants typically survive when properly hardened off. On the USDA website you will find a USDA Hardiness Map which provides information on the average minimum winter temperature in your location, by zip code.
It should be understood that a USDA zone only refers to winter low temperatures and not the overall growing conditions for your area, such as rainfall, summertime temperatures, season length, soil quality, chill hours, or any other factors that go into successfully growing your plum trees.
To regulate hormones and produce healthy flowers and fruits all plants must undergo a period of dormancy. Dormancy, which is like a kind of sleep for plants, is triggered by what we call "chill hours" or "chilling hours" - a period of time where the temperature is between 32 and 45 degrees Fahrenheit. Different varieties of plums will require different amounts of chill hours, with cultivars requiring less than 600 hours being considered "low-chill".
Both European and Asian plums have standard-to-high chill hour requirements at 700-1000+ for most varieties, with a few exceptions.
If you have questions about the chill hours in your area contact your county Agriculture Extension Office to get your local details!
Plum trees need to be planted where they receive at least 6-8 hours of direct sunlight as measured in early summer (late June to early August). Sufficient sun exposure triggers the initiation of new flower buds for the next growing season, without which there will be no fruit. Fruit ripening and flavor development are also benefited by the carbohydrate production stimulated by the sun, as well as the sun's heat.
Plum trees tolerate a wide variety of soils, but a well-drained sandy loam soil at a pH of 6.5 is ideal for growing plums. Improve your soil where you intend to plant by mixing an inch or two of composted organic matter, aged manure, or leaf mould into an area 2 times the diameter of the planting hole and up to a foot deep. A 2-4” deep layer of mulch (straw, leaves, or wood chips) applied after planting will continue to improve the soil and maintain moisture.
Allow sufficient space for both the top of the plum tree and its root system when selecting the planting location. Refer to size descriptions for each variety, keeping in mind these are generally managed or pruned sizes, not maximum potential sizes. If you are planting an orchard be sure to include enough space between rows for healthy airflow and for transporting your supplies in and your fruit out.
Due to the large size of plum trees most European and Asian plums are not good candidates for container growing. There are some complex crosses, like the nectaplum, that are bred and grafted specifically for container growing and can be considered for a container growing environment.
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. 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 under mulch work very well.
For good steady growth and high productivity, your plum trees need to have adequate amounts of various mineral nutrients. Many people are fortunate and have naturally rich fertile soils with the neutral to mildly acidic pH that fruit trees need to thrive. Some soils are deficient in some nutrient or another and use of fertilizers, organic or chemical, can be highly beneficial if you want your plum trees to grow well.
For fruit trees you will want to use a balanced fertilizer containing nitrogen, potassium, and phosphorous, with a neutral pH. A couple of inches of wood chip mulch is also recommended as it will not only conserve moisture and help in weed control, but also keeps your soil healthy by building up humus and maintaining a neutral pH for your plum trees to grow strong and healthy.
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 increase disease problems on your plants and can even kill them. Use of too much fertilizer, whether chemical or organic, can 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 per year and has healthy-looking foliage, it may not need much or any fertilizer.
For specific timing recommendations about spraying for disease in your location, please contact your county Agricultural Extension Service office.
Sunken blackish cankers on stems or trunk, wilting and death of branches, gummy ooze from cankers, dead dormant buds.
Copper fungicide in early fall and again in January. Cauterize cankers with a torch in early summer. Apply foliar or soil drench micronutrients to aid tree immune system.
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.
Wilting and death of twigs and blossoms. Fruits turn rotten, gray-brown in color, often hanging from the tree as “mummies”.
Promptly remove any infected twigs or mummified fruits. Apply copper, sulfur, or lime-sulfur fungicide at petal fall, midsummer, and again in fall.
Blossom brown rot can be a difficult problem in very wet spring seasons. Spray promptly as soon as dry weather permits.
Invades apples, chestnuts, cherries and other trees. Pin size holes in trunk spring or summer. Look close to see sawdust around hole and notice fermented smell. Limbs or whole trees suddenly die.
No effective chemical organic methods exist currently. Mechanical control can include inserting a stiff wire, like a straightened paperclip, into each hole and forcefully poking to injure or kill the insect within. Repeat within each hole as needed. Whitewash trunk and lower limbs with interior white latex paint diluted 50% with water in fall to confuse beetles next spring. Infestations bad some years. Borers live in alder and other trees.
Bark beetles sense volatile oils from stressed trees. Keep trees healthy, particularly when newly planted. Monitor and destroy infested trees. Generations occur April-May, June-July and August-September.
Dark olive green slug-like larvae that skeletonize leaves. Especially common in summer months.
Insecticidal soaps (e.g. Spinosad). Pyrethrin, rotenone dust, or bioneem. Pick off and destroy by hand.
Trees can tolerate up to 25% defoliation with little harm. May also infest plum, cherry, hawthorn, or mountain ash trees.
Small barnacle-like bumps on branches and leaves. Caused by insect.
Dormant oil spray in early spring.
Insecticidal soap or soap/oil spray during juvenile phase.
Browsed shortened branches. Leaves are obviously munched on, removed, or plants are pulled up.
Fences or cages at least 8’ tall. Plastic mesh, electric, or woven wire fences.
At Raintree, an 8’ woven wire deer fence has worked best. Repellents don’t work consistently and, aside from fencing, only trained large dogs patrolling the perimeter are effective.
Fruits disappear or have gaping holes in them. Strawberries, blueberries, cherries and filberts are most susceptible but most fruits suffer occasionally.
Reflective Bird Scare Tape can work well. Bird netting. Cages. Decoy owls can work well if solar-powered with head movements and when multiple posts are present to move decoy weekly.
Blue Jays start harvesting filberts when ready to pick, and so should you. Nuts dropped by jays are usually empty.
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.
Keep mulch 4”-6” away from trunk. Keep grass short and 1’-2’ from trunk. Use vinyl tree guard wrapped around trunk until tree is well-established. Most damage occurs during cold seasons.
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. Remove tree guards before the heat of summer can damage bark within.
1/32" to 1/8” long pear-shaped insects that multiply rapidly, especially on the underside of leaves and on stems. Can be pink, green, black or white. Leaves can show red blisters or are curled-down and stems turn black with sooty mold.
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.
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.
Numerous ants scurrying up and down the tree trunk; aphids, scale or mealybug present in large numbers, lots of sticky honeydew, perhaps sooty mold.
Find hill and apply pesticide. Apply Tangle Trap over 2-3” wide band of paper wrapped around trunk. Eliminate other pathways into tree.
Ants nurture and protect these insects in exchange for their sugary secretions. Insects may be difficult to control until the ants are controlled.
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.
Monitor with traps, some broad spectrum pesticides may work. Researchers are working on finding effective controls, but no info has been released yet.
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.
Lesions on the upper surface of the leaf, or on the fruit or stems, followed by orange-ish structures on the bottom side of the leaf, or on the fruit or stems, which produce spores.
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.
Rust diseases require an alternate host, removing the host (within 900’ radius), applying fungicides, or removing infected parts may help. Check with your county Agricultural Extension Office to see what rust diseases in fruiting plants may be common in your area, and their alternate host.
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.
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.
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.
