The plum tree (Prunus domestica) is the most wide-spread fruit-bearing tree from South-East Europe. It has been planted since ancient times for its fruits, which are used in the food industry. This tree grows effortlessly, regardless of the climatic conditions. It is a medium-sized tree, its leaves are oval and with serrated edges and its flowers are white. The plums can be consumed in various ways: fresh, dry, as jams, or as important ingredients for the alcohol industry. The plum fruits contain: sugars, organic acids, albumin, cellulose, vitamins (A, B, C), iron, calcium, magnesium, phosphorus, sodium, etc.
Growth and fruition requirements
The plum tree has a strong root system, that exploits every soil type. The plum tree often produces numerous basal shoots. These must be eliminated, as they consume the resources the tree needs to produce fruits. The plum tree’s trunk is straight and its bark is cracked. The aerial growths depend on the maintenance procedures that have been performed in the orchard. To have a proper pollination, plant at least 3 different species that blossom at the same time. During cold spring days, the pollination is weak and the production as well. The plum tree starts to bear fruit 4-5 years after planting, and it has a longevity of 30-40 years.
Climate and soil requirements
The plum tree has moderate temperature requirements. The best results can be achieved in areas where the average annual temperature ranges between 8 to 11 degrees Celsius. It can withstand temperatures as low as -31 degrees Celsius (during winter). The flower buds withstand -4 degrees Celsius temperatures, the flowers are affected by temperatures lower than -0.5 degrees Celsius. Temperatures than exceed 35 degrees Celsius will cause burns to the young leaves. The plum tree will properly grow in areas where the annual rainfalls are 600-700 mm. This fruit-bearing tree doesn’t have high light requirements and it well exploits all soil types. If the vegetation factors are at an optimum level, the plum tree will well exploit any soil type. It can even be planted on sandy soils (if there is an irrigation system installed).
Preparing the soil
When it comes to the plum tree, preparing the soil must not raise any issues. This step needs to be done respecting the general guidelines. If the plum plantation is started on a parcel that has been used for an orchard before, the soil needs to be prepared 1-2 years in advance. To restore the soil structure and take out any possible disease outbreaks, the soil can be planted using perennial herbs. If the parcel has been severely infected by weeds, the following herbicides can be applied: Roundup, Clinic, Glyphogan.
The soil can be fertilized using 20-30 tons of organic compost per hectare. It is highly recommended to plough the soil at a 60-cm depth, as it will ease the root development. If you cannot perform this procedure, plough the soil manually. All foreign materials must be gathered from the soil and eliminated from the parcel. We recommend marking the parcel for a precise planting. Marking the soil means establishing the position of each tree to the planted.
The optimum time for planting, for most fruit-bearing species is the autumn time. This rule also applies to the plum tree. The sowing material will have to be procured only from nurseries or authorized crop stations. The following planting scheme is recommended: 5-m distance between the rows and a 4-m distance between the plants on each row.
Before planting, the roots need to be cleaned up. The purpose of this operation is to removed the wounded parts of the roots and to smooth the existing root wounds. The roots that have already dies will have to be removed and the living ones need to be shortened to a 7-8-cm length. This technique helps keep a healthier root system. The roots need to be cleaned only if the seedlings were recently taken out of the soil. After cleaning the roots, they must be mulched. Mulching the roots means placing them inside a mixture of yellow soil, fresh organic compost and water. The mulching layer’s purpose is to assure a higher humidity percentage around the root system. The mulching mixture must have the consistency of sour-cream. If the planting material has been transported on long distances, before mulching, place the roots in a water filled vase for 2 hours. This technique will rehydrate the roots.
The actual planting process
This step can be started by digging the holes. If the soil was not taken care of, the holes can be dug 2-3 months in advance and must respect the following dimensions: 100 x 100 x 80 cm. If the soil was properly taken care of, the holes can be dug 1-2 days in advance, or even during the same day. If this is the case, the holes must respect the following dimensions: 50 x 50 x 50 cm.
At the bottom of the holes, pour a mixture of fertile soil, that comes from the upper part of the dug holes, and well-decomposed organic compost. Insert the tree in the holes in such a way that its roots are directly placed on the fertile layer. Once the roots have been covered using 10-cm of soil, press the soil. When planting, the roots must be in a close contact with the soil. The planting depth must be calculated considering that the grafting point must be 3-cm above the soil and orientated towards north. After planting, insert a supporting stake. The tree can be covered using anti-rodent protective materials.
During spring, unveil the protective materials surrounding the trees and apply the needed water intake. Installing an irrigation system in mandatory for young orchards. Around the trees, the soil needs to be superficially ploughed, or covered using vegetal residues (mulching). Mulching the soil will help keep it in a good phytosanitary condition, it will prevent weed growth, it will preserve the soil water and it will reduce the number of maintenance procedures that need to be carried out.
During the plum trees’ first spring, shorten the trees to an 80-cm length, above an exterior-orientated bud. Once the tree enters its vegetation period, eliminate all buds and sprouts from the trunk area up to a 50-cm height. During summer (August), choose 3-4 sprouts, evenly placed on the tree, to form the future crown. During next year’s spring, the main sprouts will have to be picked. If these are longer than 60-cm, then cut them to respect this length. The sprout that extends the main axle must be shortened so that it is 25-cm higher than the main sprouts. During summer, eliminate all greedy sprouts and the ones growing on the superior sides of the main branches. During the third vegetation year, start forming the crown’s second layer. The extension branch of the main axle needs to be cut above an exterior-orientated bud. Leave one vigorous sprout on each main branch, that is around 50-cm from the main axle and orientated towards the exterior of the crown. All sprouts growing on the superior side of the branches must be taken out.
During the fourth year, choose a branch to form the third crown layer. This must be 30-cm away from the second crown layer. Take out all competing, greedy and interior-orientated branches. To balance the fruit weight on the branches, the annual branches need to be shortened to a 4-5-bud length. To avoid severe cuts, during the first years after planting, the branches can be directed. The purpose of the cuts is not to defoliate the plum tree, but to air it and take out the vegetative growths (greedy sprouts), which consume the needed fruition resources. All cuts must be obliquely applied. This is how the water will drain away from the wounds. Wounds larger than 2-cm need to be covered with mastic.
To conduct the trees’ growth and fruition, position changing techniques need to be carried out. Such techniques are: training the branches, tilting the branches and arching the branches.
– Training the branches: this represents changing the natural branch position by making it grow vertical. This leads to the branch’s growth the garnishment. This procedure needs to be performed only for weak main branches, or for the branches that are under-developed comparing to the other ones. This process needs to be performed to young trees, growing trees and it is not favorable to differentiate the fruit buds.
– Tilting the branches: this consists of changing the branch position, by making it grow horizontal. This process leads to differentiating the fruit buds on that branch and to the crown airing. The branches can be bent beneath the horizon level as it will increase the fruition. This process needs to be carried out during the young tree stages, when the vegetative growths are predominant.
– Arching the branches: this position changing technique makes the base part remain ascending, and the upper part must be bent beneath the horizon level (descending). This process stops or slows down the branch’s length growth and its garnishment, but, at the same time, it encourages the growth of greedy sprouts on the curved areas of the branch, which is also undesirable. The trees that have had their branches arches will bear fruit 2-3 years in advance.
– Transversal incision: this interrupts the vases by finely cutting with a sharp blade. This cut must be applied above a dormant bud as it will stimulate it to enter its vegetation stage and it will garnish an area that has fewer branches.
– Longitudinal incision: a fine cut will have to be applied to the trunk. This technique helps the trunk grow in width.
– Twisting the branches: this represents the technique used to twist branches or sprouts until these easily come off the trees. This process reduces the vegetative growths and stimulates fruition. This needs to be applied to branches or sprouts that are too vigorous.
– Breaking the branches: this needs to be done to very vigorous branches as it will reduce the growth and it will stimulate the differentiation of the fruit-bearing buds.
Due to its high productivity, most of the times, the plum tree produces more fruits than it can nourish or support. If this is the case, to avoid the tree’s exhaustion and to obtain quality fruits, the number of fruits on the tree must be reduced. This process will release the tension the branches have accumulated due to the height of the fruits, it will air the tree and it will help the remaining fruits reach the specific specie characteristics (size, color, taste). The plum tree’s fruits must be reduced before the pit starts to harden. Make sure there is a 5-cm distance between the fruits. Keep the healthy fruits and the ones that benefit from direct sunlight. Eliminate all deformed, ill or underdeveloped fruits.
Maintaining the orchard needs to be done differently, depending on the location and age of the plantation. If there is an irrigation system installed, the distance between the tree rows can be planted with legumes or fruit-bearing shrubs. Examples: tomatoes, peppers, eggplants, onion, garlic, potatoes, strawberry, etc. If the soil is eroded, the distance between the tree rows can be planted with grass, or with hay, alfalfa, etc. For steppe lands, the soil must be kept clean as it needs to accumulate as much water as possible. The soil can have herbicides applied, but only 2-3 years after planting. Products that can be used: Centurion, Agil, Fusilade Forte, Panterea, Leopard.
Due to the climatic instability from recent years, the risk of having late frosts has significantly increased. Most of the times, during these late frosts, the trees have already blossomed and this compromises the production. To avoid this, the trees can be fumigated. This consists of burning easily ignitable materials that produce a large smoke quantity. Examples of products that can be used: rubber, organic compost, oily residues, peat, etc. These materials need to be gathered and placed as piles. Use around 8-10 piles for each soil hectare. This technical procedure will protect the plum trees against temperatures as low as -3 degrees Celsius.
Having an irrigation system installed in mandatory for the areas where the annual rainfall percentage is low and for the intensive orchard plantations. This helps as it increases the production and tree development. We recommend irrigating as many times as needed, to assure the trees their needed water intake. The best results can be achieved by using a localized or drip irrigation system. These 2 irrigation methods will reduce the risk of leaf diseases. We recommend using around 400 cubic meters of water per hectare per watering.
The plum trees can be fertilized using complex fertilizers, such as NPK, 300-400 kg per hectare. If the plantation only has only trees, these need to have the fertilizers applied at their bases.
The plum trees also react well to leaf fertilizers. The following products can be used: Cropmax, Amalgerol, BlackJak, Terra-Sorb.
The health of the trees is very important. A healthy orchard will produce fruits for many years. The maintenance procedures, the cuts, the irrigation system or the fertilizers, can increase the trees’ resilience against diseases and pests. For more information about the diseases and pests that can affect the plum trees, as well as the proper prevention methods, please click here.
The orchard must be kept clean. Gather the fallen leaves, clean the tree branches using a scrubbing brush in order to remove the eggs of the pests, the moss, the lichens. Only after this cleanse, the trees can have builder’s lime applied. The builder’s lime slightly sanitizes the tree and, during spring, it delays its vegetation period start, to protect the buds against late frosts.
During wintertime, the pathogens that affect the orchard plants, winter on the tree barks, in different stages. To destroy any possible disease outbreaks from the orchard, treatments need to be applied during the vegetative rest period (winter). The following pests can be successfully fought: lackey moth, aphids, acari, European fruit lecanium. These treatments will have to be applied during the first days of winter, when the outdoor temperatures exceed 5 degrees Celsius. For pest prevention, the following products can be used: Mospilan, Actara, Decis, Calypso, Fastac.
When it comes to diseases, the first treatment (after the leaves have fallen) needs to be applied using copper-based products. The second spraying using copper-based products needs to be done during spring, at the bud opening phase. The substances need to be dissolved in water and sprayed on the entire surface of the trees, from the base of the trees, up to their tips. The following products can be used: Zeama Bordeleza, Champ, Funguran. These treatments need to be applied during sunny days, with temperatures exceeding 6-7 degrees Celsius, so that the substances will not freeze on the trees. 7-10 days after the copper-based products have been applied, spray the plant with horticultural oil (150 ml for 10 l of water), such as Confidor Oil or Ovipron.
This process needs to be done once the plums have reached the consumption maturity. The optimum harvesting moment can be recognized as there are several changes at a fruit level. The fruits have intense colors, softer pulps, the sour taste is replaced by a sweet taste. The plum fruits don’t possess a post-maturing capacity. If the harvesting moment is delayed, the fruits can no longer be handled. Do not harvest by shaking or beating the branches. This will only make the fruit-bearing branches break and fall off.