Good planting practice starts with selecting the right tree for the right place, sourcing trees from reputable suppliers (including from nurseries accredited through Plant Health Alliance). Trees in urban areas are often expected to grow in challenging soils, so soils may need to be improved or de-compacted, with competing vegetation removed before planting. 

Due to climatic changes and the urban heat island effect, we find that many native British tree species are increasingly struggling to withstand the higher temperatures and drought conditions. It is important to select tree species that can tolerate harsher urban conditions whilst also considering potential further climatic changes in the future.  

At Trees for Cities, we often select species that you would find growing around the Mediterranean basin, which, due to their relative geographical proximity to the UK and similar habitats that we have here and other parts of western & northern Europe, are also more likely to provide benefits to wildlife as well.  

We do also select other species from around the world that are known to be reliable and tolerant of these changing conditions, which we also choose for their ornamental and amenity value. However, where possible, we do specify native species that are more adaptable to the drought conditions we are increasingly facing, particularly for our woodland creation projects. 

We sometimes add natural supplements/organic soil additives such as biochar, nettle tea or compost to tree pits or mixed in with water after planting to give trees a boost. We do this based on soil sample/test pit results and tree health monitoring on an as-needed basis rather than as standard. 

Our urban forest team refers to mulch as ‘brown gold’! Mulch can be any organic material such as wood chips, leaves or compost. Adding mulch as a protective layer on top of the soil around the newly planted tree is a vital element of our tree planting practice to support establishment. We are big fans of wood chip mulch.

Why is mulch so important?

• Mulch insulates the soil, helping to provide a buffer for the roots from hot & cold extremes
• Mulch retains water, helping to keep the roots moist
• Mulch keeps weeds out to help prevent root competition
• Mulch rots down and feeds the soil
• Mulch can even help reduce lawn mower & strimmer damage 

Some key things we’ve learnt when it comes to mulch:

• The more the merrier – we lay down a nice thick layer of mulch, ideally between 50-100mm, as this really makes a big difference to a tree’s establishment
• Re-applying mulch matters – we top up mulch regularly as it degrades, especially during the summer months, as we find this is key to really helping trees to establish. 

We water all our standard trees regularly during the spring and summer months for 3 years after planting. Trees in their first year of establishment are the most vulnerable, and so these trees get watered weekly. Trees in their second year of establishment get watered every 2 weeks, and trees in their third year of establishment get watered every 3-4 weeks. We also monitor all our trees’ health throughout the growing season and can increase watering for trees that are struggling as needed.

As well as watering and topping up mulch, we also weed around the base of our trees to reduce the competition for water and nutrients, as this makes a big difference when helping trees to establish. For our standard trees, we will also do any maintenance needed to repair broken straps, stakes or cages to reduce the potential for damage to the trees. Because all our trees are being monitored regularly, we are ready and able to give them any extra support they may need to establish well.

Many funders want to fund tree planting, but not the essential establishment and maintenance work that is required to ensure that trees thrive to deliver vital ecosystem services.  We are creating a Tree Care package to incentivise funders to support this important aspect of our work.  

Urban spaces comprise multiple hard surfaces such as roads, footpaths, roofscapes, paved open spaces and gardens, etc, that store heat and contribute to the creation of an “urban heat island”. This occurs when land heats up quickly and stores that heat, which continues to radiate long after sunset.  

In comparison to urban areas with plentiful tree cover and green spaces, areas devoid of trees may experience differences in local temperatures of between 5-7°C. This means urban trees face greater challenges of heat stress (i.e. leaf scorch) and a lack of water (the warmer it is, the more a tree transpires/loses water, and so the more water it needs to maintain all of its physiological processes, such as photosynthesis). This, combined with lower rainfall in our ever-warming summers and a high concentration of paved, or non-porous surfaces, means urban trees can really struggle to get enough water to establish well.

Urban spaces face growing threats from the impact of extreme weather events, due in part to dense building developments, sealed and paved surfaces, reduced vegetation cover, and limited absorbent landscapes.  

Weather conditions during and between growing season are becoming more unpredictable – mild, wet summers tend to have few failures, but hot, dry summers/periods of drought can result in more failures of recently planted trees. In response to the increasing frequency of extreme temperatures, Trees for Cities has recently adjusted our maintenance programme as follows:

• Standard tree watering - more frequent watering over the summer, complemented by a public summer campaign to encourage residents to water young street trees #WateringWednesday 
• Whip planting – reviewed our planting specification to help the trees prepare for harsh conditions, e.g. limit whip planting to Nov-Feb, mulch well and weed/mulch during the summer to give them the best chance to survive a tough summer. 
• Species selection - climate resilient species, which often means a move away from native species in our standard planting. We still plant almost exclusively native for woodlands, however.

Watering a newly planted urban woodland poses logistical challenges. We advise planting earlier in the season (Nov – Feb), increasing mulch levels and re-mulching frequently over the summer, hand-weeding around the base of whips (although this relies on large-scale mobilisation of volunteers). Further work includes reviewing the type of tree stock, how trees are stored/handled before planting, and ground prep prior to planting.