[dropcap]The [/dropcap]effect of various impacts both intentional and not, on a tree. When stress turns into distress is where you have a problem. Almost everything we do to trees in bonsai horticulture is a form of stress. Knowing how far to take any given activity at a time is the key to keeping the tree in a place where it can recover from the stress and move forward in its development with active growth, or with mature trees, remain in stasis.
Trees reveal unintended stress in a number of ways, and can often be subtle at first and then dramatic. We’ll look at a few stressors most common to bonsai which are unintentional…
Insufficient water stress is easy to spot in deciduous trees because of lack of water will cause wilting in the leaves, and eventually drooping in branches that have not lignified (turned woody). Eventually the drooping foliage will fail and die off, indicating advanced stress. Pines are less susceptible to stress from insufficient watering as they have the ability to collect moisture from the air and dew around them, but all conifers will suffer from long term deprivations as readily as any deciduous tree. Responding to water deprivation involves letting the tree and pot be submerged in a tub for at least 15-20 minutes when you discover the problem. This isn’t so much to hydrate the tree as it is the soil. Soil which has been allowed to get too dry is less prone to retaining water. For most new learners, under watering is a major problem as surface soil is often misleading, and what seems adequate is actually masking dryness deep in the pot. Also not watering thoroughly to the point of draining out the bottom of the pot can mean not all areas of the roots have actually received water. Stress from too little water can be caught and corrected, and if not protracted – have minimal long term effects.
The stress of too much water will often manifest as yellowing then browning tips on leaves and needles. Stress from too much water indicates poor soil conditions where there is too much water retention and not enough air. If you have a good soil mix which is free draining, stress from over-watering is almost impossible. But this kind of mixture is comprised almost entirely of non-organic components. If your soil has a lot of organic components overwatering can be a harder problem to correct as by the time the problem is discernable, you often have damaged the root system. This can require significant intervention to correct and you should seek species and season appropriate advice from someone familiar with the species.
Stress from too much light can result in dieback and overall browning of leaves over whatever area is facing the harshest sun – the leaves can seem crispy and brittle. This can also happen as a combination of too much sun along with not enough water. A tree in the ground is more resistant to sun scorch as it has a larger area from which to pull water and will extend its roots to find that water. Thereby preventing the dry out that hastens sun scorch. Certain thin barked species like maples can be especially susceptible. Before placing your tree in full sun, be sure that is an appropriate placement for the tree. Be aware that even the bark on a tree can burn. If you move a tree from a traditionally shady location, or remove a branch from a tree and it reveals an inner section of bark which previously has always had filtered or little light exposure, the bark in that newly exposed area may not be thick enough to cope. If you notice a section of bark is looking unhealthy, discolored or even flaking off to bare wood – but otherwise the overall tree looks fine, that area of bark has likely died. (It is important never to let bark remain over areas of the trunk which you know to be dead. The porous nature of a tree’s vascular system allows water to be absorbed and held against the tree, causing eventual rot.) When previously kept from long exposure to full sunlight, even sun tolerant species should always be gradually exposed to increasing light in order to give both foliage and bark an opportunity to build up protection to the exposure.
Stress from too little light will produce lackluster growth that will often also look very anemic. Leaves that are present will also likely be enlarged to create more surface area to catch light. Inner branches and foliage will also tend to die back, as there isn’t enough light to filter through the tree to keep them viable. Getting enough light inside the canopy to the inner branches is key to keeping healthy foliage close to the trunk.
Stress from wind exposure is most dangerous in freezing weather as sub-branches and buds can die when not protected from cold dry winds. Conversely sustained winds in hot dry times will desiccate leaves. Keeping trees in places where they will have protection from heavy wind is always advisable and in extreme conditions crucial.
Water, light, and air… are all basic to keeping trees alive. When these elements are in appropriate measure for the trees needs, the result is great health and resistance to disease. Imbalance in any of these things will distress the tree, and when let go too long, often it can take years to bring a tree back to health again – if at all.
There are times when stressors are both intentional and useful…
As mentioned earlier delaying the re-potting of a tree causes leaves and sub-branches to get smaller with progressive growth cycles. This is very beneficial to producing a refined image in a tree.
Root pruning itself is a stressor… though it often leads to vigorous health, its timing is critical and the amount of pruning to be done is very dependent on a thorough knowledge of the tree’s species, general health, and its history. Constant root pruning can kill a tree, because removing roots is the removal of energy reserves which is stored in those roots… doing it out of its time can kill a tree… some trees need to be root worked in stages, which can be done by taking out wedge sections of the trees roots rather than going through all the roots all at once. Some trees don’t flinch no matter what you do to their roots. Know your tree species before doing anything radical.
Hard pruning the foliage and branches of a tree species which is known to back-bud on old wood will stimulate the production of new buds and let you introduce taper into the structure of your tree. Timing is very important in this activity… to do this to a great percentage of the tree at the wrong time, can kill or seriously damage the health of your tree. With certain species like hinoki it is virtually impossible to stimulate back budding on old wood – so never remove all foliage from a branch. Be sure to know your species characteristics before hard pruning a tree.
Limiting food and water to control growth is not an uncommon practice among those who are attuned to the needs of the tree they are doing this too. In fact, certain species cannot be induced to heavy flowering unless they have a “drought period”. As always, the health of the tree is a critical factor in ever deciding to limit the tree in this way.
Wiring and bending branches are all injury causing actions. It is the activity of moving branches… slipping the cambium away from the sapwood to be able to move the branch significantly that causes minor damage which then heals and stiffens the branch into the new position. Not being attentive to your wiring in the season wood is added to your tree can cause damage in the way of wire scars as the tree swells around the wire. Wire is a temporary means to a temporary end (all trees need wiring work repeatedly throughout their existence). So don’t get too wrapped up in what kind of wire to use as long as it’s effective and you know how to work with it. Aluminum is great because it’s easily applied and removed, and can even be reused in some cases. Copper is great for fine work and trees which you want to be able to show formally. Copper also has great strength in a smaller gauge but is harder to handle and is more difficult to apply and remove.
Creating deadwood and scars are stressors which should not be performed on weak trees… as each wound will take energy from the tree to heal the wound. In fact… no intentional stressors should be performed on trees which are not in optimal health.
Collecting trees from their natural growing environment can be a great stressor. It can take years of patience to get to the point of being to work on a spectacular collected specimen. Some trees are easily freed from natural pockets in stone with nearly all roots in tact… but for the most part, only time will tell if the tree will survive the collection process, which is why preparing the tree for collection in the ground is an important step to take if it is possible. It is not unknown for it to have taken an entire decade to prepare for collection a single magnificent tree. The patience exercised ensured the greatest chance of success for the artist’s efforts. Do not be surprised for it to take 3 years or more to safely say a tree is ready for work post collection.
(Daniel is getting ready to debark the lenght of the lower part of the trunk on this collected tree. This is being done so that eventually the tree can be brought down to a size which can be put into a pot. For the moment, it lives on a large stone.)