14th September 2016
Mulberries come in all shapes and sizes, from the spreading black mulberry (Morus nigra), to the many cultivars of often more upright white mulberries (Morus alba). This short introduction to some of the techniques you can consider when managing your mature mulberry tree is a starting point to help you support their health. However each mulberry tree is different in regard to its specific location and issues. The considerations below are no substitute for obtaining professional advice from a competent arborist before any tree works are carried out.
Before undertaking any work you should first check that you are able to do so. Your mulberry tree may have a Tree Preservation Order, a Restrictive Covenant or be within a Conservation Area – you can check if any of these apply through your Local Authority. If it is within a churchyard you will also need to seek permission from your Diocesan office. You can find links to further information and how to find professional arborists at the bottom of this guide.
The best approach to caring for trees is to inspect them often, but undertake minimal intervention. If the tree is developing well and is healthy, it can continue to do so without pruning, mulching or other work which, however well intentioned, could reduce the vitality of the tree. However when the health of a tree is deteriorating, or an inspection reveals potential problems, maintenance work can prove beneficial. Relatively easy methods include mulching and keeping surrounding vegetation under control, whilst more technical work, such as pruning and installing structural support, need a more thorough analysis. During early stages of growth, improve future prospects by minimising competition for nutrients, water and most importantly light. Young trees are typically light demanding and will soon develop an unbalanced crown if overshadowed. Later on in life such unbalanced trees frequently collapse or need to be propped.
Regularly inspecting a mulberry tree can help to reveal potential problems and give adequate time to resolve them or contact an arboricultural consultant for advice. Inspections do not only support the tree, but are also necessary as every tree owner has a duty to take reasonable care to ensure their trees do not pose an unacceptable risk to people, including in adjacent land. Keeping records of these inspections, including notes and photographs, can help you to see changes to the tree overtime, as well as serve as evidence of your diligence in the rare event of an accident.
The stability of the tree can be assessed by looking at the structure and features of the crown, limbs and trunk. An uneven crown shape or leaning trunk can indicate the tree is at risk of collapsing. Over extended branches and limbs can fail and are often found on black mulberries in particular. A good rule of thumb is that if the limb extends beyond the tree’s canopy then it may require support. If the soil around the tree is cracked or lifting it may be the result of the tree rocking in high winds, which can be caused by a dense or abnormally large crown compared to the trunk, as well as local factors such as the wind being funnelled by surrounding buildings.
Cracks in the tree can indicate that branches may be unstable and at risk of failing, as can cavities (which may however be host to nesting birds). Fungal fruiting structures on the tree can point to decay within the tree and the potential for failure.
When the mulberry is in leaf, the number, size, spread and colour of the leaves can help you assess the vitality of the tree. If the leaves are smaller or curled it may indicate an over abundance or shortage of water or soil nutrients, or the presence of a fungi, virus or pest attacking the tree. The spotted-wing drosophila fruit fly has also become present in Britain in recent years, and may be seen during the fruiting season. The fly can spoil soft skin fruits including mulberries and is difficult to eradicate. Traps, timely removal of ripe and dropped fruit, and the use of some sprays can help to limit the fly.
Applying mulch around the base of the mulberry can retain moisture in the soil and remove competition from grass and weeds. A layer of mulch (8-10cm), such as from chippings or manure, should be well rotted and applied under the tree, but not against the trunk which can lead to it rotting.
If the tree is in an area with high footfall (e.g. a park), mulching can also reduce compaction which can damage vital fibrous roots, preventing water and gas exchange and nutrient uptake.
Black mulberries in particular are prone to having over extended limbs collapse, but props can be used to support these. In younger trees a small stake, or even a spade stuck in the ground, can provide support for the tree, particularly limbs bearing large amounts of fruit. However more robust solutions may be needed for larger trees.
Larger trees that are at risk of failing can be braced, normally by connecting cables between structural limbs, to reduce the movement of weak limbs in high winds. However this needs careful consideration and regular inspection. Specialist advice should be sought. Prevention is always better than cure. Anticipating defects and weaknesses in advance will avoid such engineering.
Pruning can be undertaken to shape a mulberry but also to support its structure and stability by reducing the crown or pruning specific limbs. However pruning wounds harm trees, especially old trees lacking the vitality of youth, and can leave the tree susceptible to disease. You should only undertake pruning when the tree is dormant, roughly 1 month after the leaves have fallen. Pruning can also affect the tree’s ability to produce fruit.
You should not prune mulberries heavily, and light pruning in stages over several years will allow the tree to recover between pruning events. Never prune more than a quarter of the tree in a year. Older mulberries in particular can have an unfavourable mass:energy ratio. They have a large mass to support (e.g. trunk & scaffold limbs) but often a relatively small canopy volume (leaves that photosynthesise to make sugars that feed the tree). As a result, reducing or thinning too much of the canopy can shock the tree, affecting its ability to sustain itself.
Royal Horticultural Society: Mulberry tree training and propagation
VETree: Training videos
Natural England: Veteran tree guide
Ancient Tree Forum: Management guides
UN FAO: Guide on utilising mulberries for fodder
Historic England: Landscape Advice Note Fruit and Historic Sites
Forestry Commission: Common sense risk management of trees
AHDB Horticulture: Identifying Spotted Wing Drosophila
Finding a professional arborist
A number of organisations can help you find an appropriate and qualified arborist to undertake specialist work. If you are unsure what work needs to take place an Arboricultural Consultant can inspect and report on your tree(s), whilst a Tree Surgeon can carry out required work. They should undertake any work to BS 3998 standards ('Tree Work Recommendations').
Arboricultural Association: www.trees.org.uk
Consulting Arborist Society: www.tree-expert-finder.co.uk
International Society of Arboriculture: www.isa-arbor.com/findanarborist
Your Local Authority’s Tree Officer may also be able to recommend a competent arborist.