The pruning of a mirabelle tree should achieve a sustainable crown of strong leading branches and a high production of fruit. This crown should be able to bear kilograms of mirabelles when the fruit ripens and also withstand rain and storms. To ensure that all leaves and the fruit receive sufficient amounts of light, the branches must not only be distributed as evenly as possible around the trunk, but must also not grow too densely.
Structure of the tree
Essentially, it depends on the rootstock whether the mirabelle tree (Prunus domestica subsp. syriaca) grows strongly or rather weakly. Therefore, it makes little sense to try to curb excessive branch growth by pruning vigorously. If only a small garden is available, you should choose weak-growing varieties of mirabelles or half-trunks when buying.
A mirabelle tree is divided into different sections from the bottom up:
- for grafted trees: rootstock and grafting point
- three to four leading branches
- central shoot (stem extension)
- fruiting shoots (thinner, richly branched branches with many flower buds)
- shoots and buds (annual wood)
Riders: vertically upward growing shoots on the leading or fruiting branches).
The fruiting branches grow on the extensions of the leading branches. These should grow as flat (horizontally) as possible. In the mirabelle tree, the flower buds form on short shoots on the perennial wood.
Clean, sharp tools are necessary for pruning to ensure smooth, clean cuts and thus rapid wound healing.
- Rose or lopping shears: for thin branches up to 2 cm in diameter
- pruning saw/branch saw: for thicker branches
- sharp knife: for smoothing the edges of the wound
- possibly telescopic shears and a telescopic saw
Fruit trees such as the mirabelle tree are quite long-lived woody plants that can reach a life and yield age of fifty to one hundred years with good care and the right location. The woody plant requires regular care in order to remain vital and provide good yields. When pruning mirabelle trees, a distinction is made between the following pruning measures.
In the first years, the focus is not on a high fruit yield, but on a rapid, vigorous development of the crown. The yield phase of the mirabelle tree begins after about 10 to 12 years; it reaches its peak only between 30 and 50 years. To promote vigor, especially high stems must be subjected to regular annual pruning. If these prunings are omitted in the first few years, the fruit tree will bear fruit more quickly, but will also form a large number of long, sturdy branches. These can fall off under the weight of the fruit and become prematurely senescent. Therefore, a training pruning has the following goal.
to build up a stable crown with supporting framework and fruiting branches
a loose crown to facilitate care and harvesting
The first pruning is usually done directly when planting the mirabelle tree. Therefore, it is called planting pruning.
In order for the fruit tree, mirabelle tree to provide good quantities of fruit in the long term, it needs regular pruning. A maintenance or monitoring pruning includes.
light thinning (prevents senescence and maintains vitality)
guarantees the exposure of lower parts of the crown
securing the tree statics (no further height and width expansion)
permanent rejuvenation (thinning of fruiting shoots)
This measure is necessary only in exceptional cases. In a rejuvenation pruning, old or neglected mirabelle trees that produce only a few young shoots are cut back vigorously into the old wood. A new crown must then be built up again from the following new shoots.
Basically, there are two times to prune a mirabelle tree. Winter pruning is generally suitable for inexperienced amateur gardeners, as the growth habit of the branches is more manageable without foliage.
- Time: end of November to end of March
- during the winter dormancy
- best in February/March
- do not prune at temperatures below -5 degrees
- cut only on dry days (risk of infection if the cuttings do not dry out)
- best time for heavy pruning
- cut out green water shoots inside the tree in June
- from the middle of August also stronger thinning possible
- Advantage: improves fruit quality
- Disadvantages: risk of sunburn, difficult for beginners
The natural shoot formation of the mirabelle tree has a strong influence on pruning. This is because, depending on where and how much pruning is done, the tree sprouts new shoots differently.
Heavy pruning leads to strong new shoots
only a few buds remain
this results in few, but long shoots
light pruning results in strong new shoots
a large number of buds remain
each individual bud sprouts only weakly
uneven pruning promotes tip growth
higher buds sprout more strongly
the crown develops unevenly
So, to prevent uneven crown growth, it is essential to prune the shoots evenly.
As a rule, fruit trees are built in a pyramid shape. This crown shape can be applied to a mirabelle tree in the form of a half trunk, high trunk or even in bush form.
The first development of a stable crown takes place during planting pruning. Already at this stage, the foundations for the later structure of the fruit tree are laid.
Step 1: Selecting leading branches
A pyramid crown consists of the trunk extension (central shoot) and three to four well-distributed leading branches, on which side shoots and fruiting wood are arranged. Since this basic structure is maintained throughout the life of the tree, special attention must be paid to the selection of the leading branches.
- Select a central shoot and three to four suitable leader branches.
- flat, strong side branches are suitable as leader branches
- should be at an angle of 45 to 50 degrees to the central branch
- must branch evenly to all sides
- should not be in a whorl on the main shoot
- best staggered in height along the trunk
- in the case of opposite leading shoots, remove the less favorable one
- cut off all too steep branches (competing shoots) at their base
Sawing off strong branches should always be done in several steps so that the weight of the branch does not cause the cut to tear and possibly damage the entire woody plant. To do this, first saw the underside of the branch at a distance of about 10 cm from the main branch about one-third. Then a top sawing is done about one to two centimeters further out. After the branch is removed, the stub is sawed off cleanly at the branch ring (slightly thickened area at the base of the branch). For very young trees with few leading branches, it is sufficient to establish two leading branches in the year of planting. The following year, when the main shoot has continued to grow and produce new side shoots, the missing leader branches are then selected.
Step 2: Wound treatment
According to new findings, it is not necessary to apply a wound closure agent to the wounds. This measure does not significantly promote wound healing. However, it is important to allow the area to dry well. Cut frayed edges as smoothly as possible with a sharp knife. Healing proceeds faster the smaller and smoother the area is. In general, avoid all wounds that are over 10 cm in diameter!
Step 3: Correct growth direction
If the selected leading branches are too steeply upward, they should be directed further outward with the help of spreading wood. Otherwise, a wide, well-ventilated and well-lit crown cannot develop. If the leading branches are still very flexible, they can also be weighted down with weights. However, the weights must not be too large, otherwise the branch is in danger of breaking. If the leading branches are too flat, they can be tied up.
Step 4: Shortening the leading branches
After correcting the direction of growth, the leading branches are shortened by one third to one half.
- always cut directly above an eye pointing outwards
- break off or cut off all shoots and buds standing on top of the branch
- only side shoots standing underneath remain
- three to four side shoots per leading branch are optimal
- this avoids competing shoots growing strongly upwards
- cut off all leading branches at approximately the same height
- this is the only way to ensure that all leading shoots grow to the same extent the following year
Step 5: Shortening and thinning the central shoot.
The trunk extension should have flat fruiting branches that fill in the gaps to the leading branches. If three to four leading shoots have already been selected in addition to the central shoot, the main shoot is also shortened. If there are still too few leading shoots, the central shoot must first be allowed to continue growing.
- Shortening the stem extension
- the central shoot should overhang the leading branches by about 15 cm
- redirect to a steeply standing side shoot
- otherwise leave only flat side shoots (approx. 90 degree angle)
- these should be offset from the main shoot
- in case of opposite shoots, cut off the less suitable one
From the following year the crown is further built up. A nursery pruning must be carried out until the onset of the main crop. The purpose of training pruning is not only to build up a stable tree crown, but also to selectively install fruiting branches.
Step 1: Remove competing shoots
In the growing season following planting pruning, the mirabelle tree has had time to regrow more or less vigorously. Pruning is best done again in late winter or early spring around the end of February to early March.
- cut back all competing shoots to the branch ring for trunk elongation
- cut back all shoots growing steeply upwards or inwards on the leading shoots
Step 2: Remove fruiting shoots
In the first few years, the goal is not to produce a high crop, but to build up the crown structure. If too many fruit shoots are left standing, the mirabelle tree will put its energy into fruit formation rather than preferentially into branch growth.
- remove all fruit shoots sprouting upwards and sideways on the leading branches
- leave only flat fruit shoots growing outwards
- preferably on the underside of the leading shoots
Step 3: Pulling up missing leading branches
If not all (three to four) leading branches were present on young trees when they were pruned, the missing shoots are now added from the main shoot.
When selecting, pay attention to the direction of growth and height of the central shoot.
Fill the gaps of the previous leading branches
Step 4: Pruning the leading branches
The strength of the pruning of the leading branches depends mainly on the sprouting of the fruit tree.
- cut more strongly when budding is weak
- cut more lightly when budding is strong
- always prune above an outwardly directed eye
- all leading branches must be cut at about the same height
- break out buds that are facing inwards (upwards)
Step 5: Shorten main shoot
If there are three to four well-developed leading shoots in addition to the main shoot, the main shoot is also shortened. This should overhang the leading branches by about 20 cm. However, do not shorten the central shoot just anywhere, but redirect it to a weakly growing, steep secondary shoot.
The aim of pruning in the following years is to further build up both the leading branches and the central shoot. In addition, fruiting branches are installed.
Step 1: Check the angle of the leading branches to the trunk extension
With each pruning, the leading branches are always reshaped first. Check that the leading branches are still at an angle of about 45 degrees to the central shoot. Any remaining corrective wood or ropes are removed in advance.
- spread off leading branches that are too steep
- Tie up leading shoots that are too flat
- up to a length of one to two meters: Angle of 45 to 50 degrees (depending on the desired tree size).
- from then on somewhat steeper upwards (about 30 degrees)
- always pull all leading branches at the same angle and length
Step 2: Position of the leading branches among each other.
Also check if the individual leading branches are equidistant from each other.
- Check the angle between the branches
- for four leading branches: 90 degrees
- with three leading shoots: 120 Gad
- If the angle is not correct, spreading or tying can help here as well.
Step 3: Shorten leading branches
The leading branches of the mirabelle tree are shortened in length annually until at least the 6th year of growth.
- stimulates the formation of lateral branches
- always leave only one extension shoot (or bud at the end of the shoot)
- leading branches must not fork at the tip
Step 4: Establish fruiting branches on the leading shoots
Once the basic structure of the crown is established, the first fruiting branches are slowly promoted.
- the first fruiting branch must be allowed after 50 cm from the trunk at the earliest
- fruiting branches should always run flat outwards
- preferably slightly ascending (not sloping downwards)
- if necessary, correct with a spreader wood or string
- at a distance of at least 40 cm another two to three fruiting shoots follow
- Do not shorten fruit shoots
- must never be thicker than the leading branch
Step 5: Establish fruiting shoots on the central branch
Only fruiting wood that is at a suitable angle to the trunk extension may be left on the central shoot as well.
only allow fruiting branches on the central shoot that are at a shallow angle (about 90 degrees)
remove all steeply standing fruiting shoots on the stem extension
direct fruiting wood to the side that obscures the leading branches below it
After the twelfth to fifteenth year of standing, as a rule, in the mirabelle tree crown formation is completed. The main work of pruning is to maintain the crown.
For this purpose, the following measures are necessary:
- remove all inward growing shoots on the leading branches (and side shoots).
- fruiting shoots remain even if they grow on the top of the leading branches
- cut the top of the leading branches free of branches
- shorten too long leading branches and build them up again
- all leading branches must remain about the same height
- shorten too long fruiting wood (redirect to upward pointing shoots)
- the further out the fruiting branches are, the shorter they must be
- cut back tilted side branches to young shoots
- keep stem extension free from strong side shoots
- a height limitation is possible on the redirection to a side shoot
Neglected mirabelle trees that have not been pruned for a long time develop a dense crown and hardly show any young shoot formation. The mirabelle tree still bears fruits, but they are very small and some of them do not ripen. In this case, a radical rejuvenation pruning can remedy the situation. Rejuvenation pruning, just like monitoring pruning, removes all branches and twigs that are too dense. However, since no pruning has been done for a longer period of time, significantly more and also thicker branches must be taken out here. The old, downward hanging fruiting wood is also cut off. In contrast to monitoring pruning, secondary shoots and fruiting wood must also be shortened in addition to the leading branches for new shoot stimulation. However, this radical pruning should not remove more than 40% of the crown volume.
- Remove competing branches (too steep side branches).
- shorten side shoots that are too long
- the higher in the crown, the shorter
- cut or redirect steep side branches
- Cut off (or severely shorten) all side branches that cover the leading branches
- Thin out water shoots (steeply upward growing, thick branches)
- remove fan-shaped shoots at the tips
- Cut back side branches
- the further out, the shorter
- shorten too flat (tilted) leading branches and rebuild (flat shoot on top)
- cut back drooping fruiting shoots to young shoots
- strongly reduce dense branching
- thin out water shoots
- leave weak and flat shoots standing