Why do new plantings “die” in cities? The most common mistakes and how to prevent them
Why do new plantings “die” in cities? The most common mistakes and how to prevent them
A new planting in the city can look like a well-placed full stop: fresh soil, stakes, neatly laid bark, sometimes a sign with the species name. Visually, everything adds up. In practice – this is only the beginning. A tree planted in an urbanised space does not start from the level of “development”, but from the level of “adaptation”. First it has to regain balance after transplanting, rebuild its root system, learn the local microclimate, and only then can it start to put on real growth.
And it is precisely at this point that the problem appears, which residents see more and more often: the tree “is there”, but as if it were not. The leaves are smaller, the crown is sparser, in heat it wilts faster than plants in a pot, in winter after salting the curbs it starts to look worse than in the previous season, and after two/three years it is sometimes simply replaced with a new one. In investment statistics it is still a “completed planting”. In reality it is a loss of money, time and – importantly – social trust in the very idea of greening.
It is therefore worth putting the perspective in order. The death of young plantings is rarely a matter of “bad luck”. Most often it is the consequence of repeated mistakes: poorly prepared soil, too little root space, improper planting, species selection without taking urban stresses into account, and maintenance that is carried out “for order”, not for the biology of the tree. In the following parts we will go through these mechanisms calmly and as formally as possible – so that on the one hand they are understandable, and on the other hand they can be implemented in practice. The One More Tree Foundation declares as its goal tree planting in Poland and Europe, but at the same time it emphasises a broader environmental and educational mission. One More Tree Foundation In its materials it also highlights the importance of an expert approach to planting and of caring to increase the chances of survival of planted trees. One More Tree Foundation This approach puts the topic in good order: success does not end with planting – it begins with the conditions the tree receives for the years ahead.
The city as a stress environment: what really burdens young trees
In natural conditions, a tree grows in a system that acts like a shock absorber. It has litter that protects the soil from overheating and drying out. It has the neighbourhood of other plants that stabilises the microclimate and limits gusts of wind. It has soil in which structure, porosity and biological life build conditions for a constant exchange of water and oxygen.
In the city this shock absorber is weakened, and sometimes it is not there at all. A tree is most often planted surrounded by impermeable or semi-permeable surfaces that direct water away from the root zone. The substrate is often compacted by construction works, pedestrian and vehicle traffic, and above it there is an additional thermal stress: asphalt and concrete heat up, give off heat in the evening, creating so-called urban heat islands. In addition, there are chemical factors, including road salt, and mechanical factors: damage to the trunk, breaking of branches, unskilled mowing and trimming of grass, as well as the effects of bad staking.
As a result, a young tree in the city almost always lives “on credit”. A limited root zone means fewer possibilities to take up water. A worse soil structure means less oxygen. Exposure to heat and wind means greater evaporation from leaves. If we add improper planting to this – that is, above all wrong depth and incorrect work with the root ball – we get a situation in which the tree fights for survival instead of building growth. This difference is particularly clearly visible in the first three seasons.
It is no coincidence that many standards and guides emphasise that it is precisely the first three years after transplanting that are critical in terms of irrigation and maintaining adequate moisture in the root zone. In this period the tree is only just “establishing” itself in a new place and is much more sensitive to drought and fluctuations in soil conditions.
“The establishment” of a tree – what does it mean in practice?
In everyday language, “it has established” means that the tree has leaves and “has not dried out”. However, this criterion is misleading. A tree may keep leaves thanks to resources accumulated before transplanting and thanks to ad hoc watering, while at the same time having a root system in poor condition. It may look satisfactory in the planting season and only show symptoms of the problem in the following year. From the point of view of biology, a more adequate question is not whether the tree “survived”, but whether it began to develop roots stably in the new substrate and whether its shoot and leaf growth is consistent with the potential of the species under the given conditions.
This distinction is also important in the management of greenery: if in contracts and project handovers we assess only the “alive state” in the short term, we systemically encourage superficial actions. The tree is supposed to look decent at the time of handover. Meanwhile, real success of plantings becomes apparent only when the tree goes through at least two–three growing seasons without a water crisis and without a clear degradation of the crown.
Urban soil: why it so often is the “lowest common denominator”
Many problems of young plantings come down to soil, although it is rarely talked about directly. In the city, soil is treated as a material to fill space, not as a living system. Meanwhile, a tree functions as well as its root zone functions. If the soil is too compact, porosity decreases, and with it access to oxygen and the ability of water infiltration decrease. In practice this means a situation in which even regular precipitation does not have to translate into real watering of roots, because water runs off the surface, or stays in the upper layer and quickly evaporates.
Soil compaction is one of the most frequently observed problems in the urbanised landscape. It is directly indicated that compaction reduces the number and size of soil pores, which are crucial for delivering both water and oxygen to roots. As a result, in such conditions it can be “almost impossible” to successfully establish plants.
At the same time, urban soil often has a discontinuous structure. It may consist of layers with different parameters: on top a thin layer of “fertile soil”, below bedding, rubble, sand, and even lower a base compacted under the pavement. From the point of view of roots, this is a physical and hydraulic barrier: roots do not pass freely, and water does not circulate naturally.
As a result, it happens that a young tree lives in something that resembles a large pot buried in the ground. Professionally, this is sometimes referred to as the “bathtub effect” – the planting zone is different from the surrounding substrate, which makes water and roots behave unnaturally. If in addition the walls of the pit are smoothed by tools or an excavator (especially in clay soils), a surface of increased tightness is created, which hinders the migration of roots outward. And again – from the outside you can only see the “tree”, you cannot see the cause.
Space for roots: a topic that should be planned like infrastructure
In the discussion about urban greenery, one often talks about the number of planted trees. Less often one talks about whether each of these trees has conditions to grow up. Meanwhile, the key resource is not so much space “at the trunk”, but space “underground”. In practice this means the volume of available, possibly good-quality soil in which roots can grow for years.
In cities around the world, this issue is increasingly approached in an engineering way, creating guidelines on the minimum volume of soil for trees depending on the target size and spatial conditions. Such an approach emphasises, among other things, that planning the underground environment must take into account the available soil volume, as well as solutions improving infiltration, such as permeable pavements.
The translation into everyday practice is simple. If we plant a tree in a place where each side of the root zone is limited by a curb, a foundation, installations and the pavement subbase, then in fact we condemn the tree to function in restriction. This restriction does not always lead to quick death, but very often leads to long-term stagnation and susceptibility to stress. And stress, combined with drought, salt and mechanical damage, can “finish” what a bad location started.
Planting: the moment when it is easiest to make a mistake with long-term consequences
Planting a tree is a logistical and biological operation at the same time. Logistics are often well refined: date, transport, pits, materials. Biology is often overlooked, because it is not visible at first glance. And it is precisely in biology that the mistakes are hidden which cost the most in the city.
Planting depth and the “root collar”
One of the most frequently indicated critical mistakes is planting too deep, i.e. placing the point where the trunk transitions into roots (the so-called root collar, and in practice also the distinct flare at the base of the trunk, referred to as the root flare) below the ground level. The effects do not have to be immediate. They often appear gradually: deterioration of gas exchange, higher risk of problems at the base of the trunk, reduced stability, and susceptibility to disease.
This is not a problem “from the realm of opinion”. Studies have directly analysed the impact of planting depth on the survival and development of ornamental trees. In works comparing correct planting with deep planting, clear differences in condition and survival were shown, and planting with the “flare” lowered by a dozen or so centimetres is treated as a significant burden for the tree.
In urban practice, this error can result from several overlapping causes. First, nursery stock may already be planted too deep in the container, which makes planters follow the “soil level in the pot” rather than the tree’s anatomy. Second, after planting, soil and bark are often piled up in a mound to “look nice” or “hold moisture better”. Third, in places with poor water runoff, people try to compensate for soil settlement by adding more soil. Each of these elements may lead to a situation in which the trunk is located in an environment that should surround roots – and this is an unnatural arrangement for a tree.
In many planting guides, the need to keep the trunk in the correct position and to expose the so-called trunk flare is emphasised, and in heavy soils it is even recommended to plant with a slight elevation of this point above the ground level, precisely to avoid oxygen deficiency in the root zone.
Working with the root ball
The second key issue is the root ball. A tree from a container or with a balled root system is not a “blank slate”. Roots may be twisted, may circle the ball, may form a spiral that later translates into mechanical weakening and developmental disturbances.
In practice, this means the need for real verification. It is not always convenient on a construction site, not always quick, but it is fundamental. The tree is supposed to form roots in the surrounding soil, not continue life in the geometry of the pot. If the ball is “closed” and the roots do not tend to spread outward, even ideal watering may not bring the expected results. The tree will use a limited water resource, and after it is depleted a crisis will appear.
Backfilling and “improving” the planting pit
In urban practice, there is often an impulse to pour a lot of “good soil” into the planting pit or to mix it intensively with additives. The intention is understandable: to improve starting conditions. The problem is that too great a contrast between the soil in the pit and the soil around it can make it harder for roots to migrate and for water to drain naturally. The result may be water stagnation within the pit or, conversely, rapid drying of the “island” of better soil if the surroundings are more permeable. The safest approach is to treat the pit not as a “pot”, but as part of a larger environment that should be as uniform and predictable as possible for roots.
Post-planting maintenance: why three years is a standard, not a luxury
Many cities and organisations that plant trees in roadside strips operate with a practical assumption: for the first three years the tree requires regular inspections and watering, and only afterwards can one speak of transferring it to “standard maintenance”. This model is directly described in educational materials on caring for new street trees, indicating a three-year period of more intensive care as an organisational norm, not an excess.
This approach stems from physiology. After transplanting, a tree loses part of its root system. Even if the ball is large, the root-to-crown ratio shifts unfavourably. The tree therefore has to balance: reduce transpiration (i.e. water loss through leaves), while at the same time initiate root regeneration and create new root hairs that will take up water from the surrounding soil. If drought or too large fluctuations in moisture occur in this key time, the regeneration process slows down and the tree enters a stress spiral.
Watering: less “often”, more “effectively”
In cities, two extremes are most often encountered: either watering is symbolic, or it is frequent but shallow. In both cases, the effect can be similar – the tree does not build a deep, stable zone of active roots, and the soil works in a “wet–dry” cycle at the surface.
Good watering of a young tree is not about water “appearing” at the trunk. It is about moisture reaching the root zone and remaining there long enough for roots to use it. In guides on the survival of newly planted trees, it is emphasised that adequate soil moisture is particularly important in the first three years after transplanting. At the same time, it is pointed out that both water deficit and excess can be stressful, because excessive moisture reduces air space in the soil and lowers oxygen availability. In practice, this means the need to move away from watering “by the calendar” in favour of watering “by conditions”. If the soil is constantly wet and the area around the trunk resembles mud, it is just as problematic as drying out. If, on the other hand, water runs off the surface because the soil is sealed or compacted, the method of application must be changed: slower, longer, in a place where water has a chance to soak in. The One More Tree Foundation, as part of employee volunteering activities, describes cooperation in which planting actions are part of a broader pro-environmental plan, not a one-off gesture.
Mulching: a maintenance tool, not a decoration
Mulching is one of the most effective practices supporting young plantings, but only if it is done correctly. Its purpose is quite formal: to limit evaporation, stabilise soil temperature, limit competition from weeds and grasses, and gradually improve soil properties thanks to the decomposition of organic matter. The problem arises when mulch becomes a “mound” at the trunk, i.e. the so-called “mulch volcano”. This is a common practice and, at the same time, harmful: it keeps moisture at the bark, promotes rotting processes, covers the root collar and may limit the development of a proper “flare”. It is directly warned that this way of mulching can be deadly for trees and increases susceptibility to disease and stability problems. Formally correct mulching therefore assumes leaving the trunk “free” and concentrating the material on the soil surface in the root zone, in such a way as to support the soil, not the trunk.
Technical and maintenance inspections
Maintaining a young tree in the city requires regular, though not very time-consuming inspections. In practice, this involves checking a few things: whether ties and stakes are rubbing the trunk, whether wounds have formed, whether the crown shows symptoms of drought, whether soil or bark has been added around the trunk, whether the watering basin has been filled in, and whether the lawn is creeping too close to the trunk, which leads to mechanical damage during mowing.
These are activities that require organisation at the scale of a city, but at the scale of a single tree they are simple. The biggest mistake is that after an investment is handed over, the topic “disappears” for a year. And a young tree in the city does not get a year of rest – it gets a year of tests.
Species selection: aesthetics is not enough
In urban practice, species selection often begins with appearance and growth rate. Formally, it should begin with an analysis of the site. This site can be described quite precisely: street type and wind exposure, the presence of reflective surfaces and degree of heat-up, the ability to water during heatwaves, the risk of winter salting, the available soil volume, and the risk of mechanical damage.
It is worth remembering that an “urban species” does not mean an indestructible species. It means a species with a higher tolerance threshold for typical stresses, but it still needs the basics: oxygen in the soil, water during drought periods, and space for roots. It happens that the species choice is correct and yet the tree dies – because the site’s infrastructure is inconsistent with its requirements. It also happens the other way around: a species is average in terms of tolerance, but it has good soil and water conditions, so it grows well.
The formal recommendation is therefore as follows: species selection should be the “second step”, after ensuring conditions in the root zone. If the root zone is weak, no species will be a long-term solution – it will only be a more or less costly attempt.
Salt, drought, overheating: three factors that most often “close” the problem
In many Polish cities, trees in roadside strips lose out particularly clearly in three situations: after winter, in the first heatwave, and during periods of long drought without rainfall. These three moments are a test that exposes weaknesses that were previously invisible.
Salting causes osmotic stress, damages roots, and in spring shows symptoms on leaves and shoots. Drought reveals limitations of soil volume and errors in watering. Soil overheating and strong insolation make shallow roots lose water faster than they can take it up. If soil compaction is added to this, the problem grows exponentially, because water does not soak in where it should, and oxygen does not reach roots even when watering is carried out.
In this sense, the death of a tree is not a “sudden event”. It is the result of an accumulation of stresses that were foreseeable already at the planning stage of the planting.
How to prevent it: a quality standard instead of a one-off action
The most important shift in thinking is organisational: a tree in the city is a multi-year project, not a one-day event. This means the need to build a quality standard that covers the planning stage (site and soil volume analysis), the planting stage (including especially correct depth and work with the root ball), and the maintenance stage (watering and inspections for at least three seasons).
It is worth emphasising the importance of correct planting depth and correct treatment of the “flare” zone, because this is an element that often determines years of further functioning of the tree. If we plant too deep, we give the tree a structural problem that is then hard to reverse. Studies on the impact of planting depth on tree survival show that deviations from the correct level may be associated with deterioration of condition and a drop in survival.
At the same time, it is worth treating soil as an element of urban infrastructure. If the substrate is extremely compacted and soil pores are limited, plants do not have conditions to root, which is emphasised directly in studies on soil compaction in the urban landscape.
The tree does not need perfection, it needs consistency
In cities it is easy to fall into the trap of a symbol: we count new plantings, take photos, and close the investment. Meanwhile, the tree “works” on the scale of years. If we provide it with consistent conditions – correct depth, a real root zone, soil with a sensible structure, reasonable protection against drying out, and consistent watering during the establishment period – the chances of success increase radically. If, however, we treat planting as the finale rather than the start, we will repeat the same scenario: a new tree for a while, and then another.
