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Establishing plants in hot dry weather

Oops – 3 years seems to have shot by since I last published a blog! Pandemics, workload and economic vagaries seem to have taken over – but climate change must remain our main long-term concern.

The extreme heat and drought of last summer made challenging conditions for the establishment of new planting – and I saw a lot of new planting perish. When I worked in Australia the first consultant in a landscape design team was often the irrigation specialist. Drilling a bore for water supply and installing a sophisticated irrigation system was a given.

Whereas some high-end UK schemes in the UK already include irrigation – I cannot yet imagine this becoming the norm for landscape schemes in the UK. Good irrigation equipment is expensive and it has to be properly maintained to be efficient. Ideally you need a cheap water supply. Using potable mains water is expensive and questionable practice (and chemically purified water is not ideal for plants anyway).

There are a number of other issues we can address first. Good soil management is paramount. A well textured soil with good organic content can hold a lot more water – which has benefits for both sustainable drainage and plant growth. Ensuring healthy soil is delivered in landscape areas is essential.

Mulches are also important, both for holding water themselves but also reducing evapotranspiration from soils and suppressing weedy species that can compete for water.

Specification of more drought resistant plant species is now widely accepted – but I also think the composition of planting designs is very important. Cover and shade from trees and larger shrubs can help to stop soils drying out and maintain air humidity – with benefits for both plants and other species – including us!

For plant establishment I think winter planting of bare root stock is preferable. Milder winters mean that roots can begin to grow and establish good soil contact right away. Drier springs mean that later planted stock may immediately become stressed with lack of soil water.

My view is that all these considerations are still more important than installation of irrigation equipment. I also think that some sorts of tree shelters are unhelpful in hot dry weather – literally helping to bake the young plants they seek to protect. In my experience a simple spiral guard often seems to lead to higher success rates in plant establishment.

Goldsmith Street

I took a quick look around Norwich City Council’s Goldsmith Street development last month, a few days after it was awarded the 2019 Stirling Prize. I personally like the architecture and some of the building detailing is really well done – the doorways probably deserve their own prize!

As a landscape architect I was particularly looking at the external works – which are notable because they show that a simple landscape design, well implemented and using decent materials makes a world of difference to any setting. I particularly noted the boundary fencing – a combination of grilles with climbing plants and timber on metal framing that seemed to provide privacy without dominating and a distinctive character.  

It was also good to see the inclusion of street trees! It is sad that I am having to say that – but on so many schemes I have worked on in recent years, someone (generally the highways authority) makes it impossible to include trees along a street. Perhaps it helps when the client is the highway authority! To me trees do so much to enhance a streetscape. That said – some of the tree pits looked a little small – so it will be interesting to monitor how these trees establish in coming years.

On so many housing schemes the external areas look like they have been implemented grudgingly. I hope the care that has clearly been taken on delivering this scheme will set the standard for all new housing in coming years.

2019 Tree disease updates

It was depressing to read in July 2019 that outbreaks of Oak Processionary Moth, Thaumetopoea processionea (OPM), had been reported across Britain – the length and breadth of England and also in Wales and Scotland. The culprit appears to have been infected oak trees from Holland and Germany. The Forestry Commission has led operations to eradicate the caterpillars – but given how the moth has spread in the home counties since it was first found in 2005, I am not hopeful that it will be contained. Additional restrictions have been placed on imports of oak trees (but why not just ban them?).

OPM is a problem because an infestation of the caterpillars will strip a tree of all leaves and leave it vulnerable to drought and disease. But another major concern is public health. The hairs of the caterpillar can cause rashes, eye irritation, breathing difficulties and even anaphylactic shock. The nests are full of their hairs. This is not a pest we want in our public parks! When local authorities are already creaking under cutbacks – the thought of perhaps having to spend thousands of pounds every year on controlling OPM outbreaks is unwelcome. It will be essential to report any suspected outbreaks. Plenty of information is available about OPM identification on the internet.

I also remain extremely pessimistic about the future of Ash trees in the UK. I was horrified to see the number of dead ash trees in Kent and Sussex when I visited this summer – and the majority of ash trees in Norfolk now seem to be in decline. The last two hot dry summers are unlikely to have assisted their plight. A five-year trial by Forest Research that begun in 2013 has unfortunately been unable to find a disease resistant strain of common ash.

Even the bomb-proof Leyland Cypress is not having its own way! I have noted a very obvious increase in the incidence of dieback in cypress trees and hedges all over East Anglia. The culprit appears to be the canker causing fungus Seiridium – of which there are at least three species. Although removal of dead branches, feeding and soil improvements may help prevent spread – this disease is likely to kill most trees once they are infected. Again, hot dry summers could be helping to make cypress more vulnerable – especially as they are typically a shallow rooting tree.

On site soil management

What do these areas of concrete waste on a building site all have in common? You may guess. They were the proposed garden areas on a scheme I was working on this year!

And sadly, this job was not regenerating a brownfield urban plot – this site was pristine arable land a few months before the photographs were taken!

Unfortunately this is not an uncommon sight for a landscape architect – and it is frustrating because rectifying a mess like this costs the project money – money that could be profit!

To rectify areas like this – firstly, all the waste materials will need removing (cement and other waste materials are generally toxic to plants). The underlying soil will probably be contaminated as well and may also need to be removed. Compacted soil will need to be broken up to ensure it is free-draining – and this may be problematic if adjacent pavements and other features have already been completed. Then new soil will need importing - both subsoil and topsoil may be required. Imported graded topsoils often have little structure and will generally need the addition of organic material and careful cultivation for several years before they provide an optimal medium in which trees and shrubs will thrive.   

But with a bit of thought and planning all this hassle and cost can be avoided. Future garden areas should ideally be made into construction exclusion zones – with the erection of secure fencing at the outset of the project. Temporary ground protection around a building area can include scaffold boards or crushed aggregate over a geotextile. These can help to prevent soil compaction and soil contamination, can be easily removed at the end of works, and they have the benefit of also providing all-weather access throughout the build.

Existing site soils should be carefully stripped and stored through the build. The natural soil from the site will always be the best soil to replace in garden areas. But soil must be kept clean and healthy throughout the construction period. The Construction Code of Practice for the Sustainable Use of Soils on Construction Sites was published by Defra in 2009 but it is still a little-known document. 

RMA can assist project teams in preparing Construction Environmental Management Plans (CEMPs) and Landscape and Ecological Management Plans (LEMPs) for most projects – and if correctly implemented they should be able to save the project money and get a better end product. Why would any development team not want to achieve those twin goals? 

Designing to withstand extreme weather

One of my lasting memories of 2018 may be the large number of dead trees I saw during the hot summer. But will it be unique? The forecasters are saying extreme weather events like this will be more common in coming decades. And remember 2018 was also notable for flooding last winter and a very late cold snap in the spring.

Extreme weather is likely to cause stress to amenity planting – especially when plants are not fully established. All the casualties in my photographs were at one supermarket site – where there were perhaps 50 dead trees, some of which were semi-mature stock that had probably cost £2000 each to supply and plant. What a waste!

I suspect the real culprit for these losses was poor planting preparation. I know for a fact that these trees were planted during a very wet winter several years ago – where the construction process had totally trashed the external areas prior to planting. I suspect they were all planted in overly compacted soils, and many of them appear to be in very restricted planting areas. So, in a year like 2018, they most likely stood in waterlogged conditions all winter and were then baked in soils incapable of holding moisture all summer.

If the ground conditions in planting areas are poor, it doesn’t matter how good your tree and shrub stock is - it will struggle to survive, especially during challenging weather. I therefore always try to advocate three cardinal rules:

Always allow sufficient space for plants to thrive. A tree is unlikely to grow to maturity in a 1x1m tree pit in the middle of a car park!

Ensure excellent drainage and healthy soil structure. You cannot provide healthy soils if the ground is waterlogged in winter and baked dry in summer.

Ensure establishment maintenance. If we are to expect regular hot summers, watering newly planted trees and shrubs will be essential. Adjusting stakes and ties and controlling weeds are also important.

None of this is rocket science – but the scale of losses I witnessed in 2018 suggests that these simple rules are, sadly, not regular practice.

Climate change will make amenity planting in our urban areas even more important in coming decades – to provide shade and to buffer temperatures and humidity. We need our new planting to survive and be sustainable in the long term. We must spend the money on good establishment practice. Remember the old adage – there ain’t no point in planting a $100 tree in a $1 dollar hole!

The growing impact of tree diseases

A concern of mine for 2018 is the continuing impact of two, now common, tree diseases. The first is Chalara Ash Dieback – which was first identified in the UK in 2012, having killed up to 80% of all ash trees in some parts of continental Europe in the previous 20 years. The second is the Cameraria leaf miner – first recorded in Greece in the 1980s and first noted in Britain in 2002.

Chalara Ash Dieback is a fungal disease (now being called Hymenoscyphus fraxineus) that was first identified spreading in an asexual form, but now seems to be found spreading sexually, with fruiting spores appearing on the previous years leaf litter between June and September. I personally first noted it affecting trees in West Norfolk in 2015 – but it appears to have spread rapidly in the last three years and I now believe it is widespread in Norfolk and throughout East Anglia. I have been monitoring a young woodland shelterbelt near my home, which is approximately 50% ash, and by the summer of 2017 about 25% of the ash trees were dead and another 25% looked stressed (see photo). Nevertheless, some of the ash in this stand still appear entirely healthy – and experts do believe a proportion of ash trees will show resistance.

Having noted the spread of the disease and the apparent rapid decline of both young and old ash trees in Norfolk, I remain somewhat sceptical that a significant proportion of ash trees will survive – especially as the fungus has now been shown to be spreading sexually. This is likely to lead to new, perhaps more virulent, strains of the disease in coming years. (It is often forgotten that Dutch Elm Disease first became a problem in Britain in the 1920s and 30s, but it was the arrival of a more virulent strain that eventually decimated the British elm population in the 1960s and 70s).

The widespread loss of Ash trees in many of our landscapes will be quite catastrophic. Ash is one of our commonest trees – both in urban and rural settings. In many settings it is the dominant large hedge tree and it often forms a large proportion of mixed native woodlands.

A second ‘disease’ which is now apparently ubiquitous in southern and eastern Britain (but I have noted – perhaps not so much in western counties and Wales?) is the Cameraria leaf miner, that now brings an unseasonal ‘autumn’ to most Horse Chestnuts as early as July. The easily recognised browning of leaves is caused by the larvae of the tiny moth Cameraria ohridella as they burrow inside the leaf.

Cameraria has generally been considered a cosmetic problem – but it stands to reason that if trees have their growing season curtailed three months early each year, that this will eventually lead to a decline in vitality. Anecdotally, during my travels in 2017, I noted many large Chestnuts showing obvious signs of significant stress, with large dead branches in the crown and strong evidence that they were in terminal decline. I am thinking that a critical point may have been reached with the trees relationship with Cameraria – and it is now well established that trees with the leaf miner seem more susceptible to other diseases such as Bleeding Canker (Pseudomonas syringae pv. Aesculi).

Although Horse Chestnut is not a native British species, it is surely one of our finest and commonest large flowering trees. If we lost Chestnuts and Ash from our landscapes in coming years it would have a significant adverse impact on landscape amenity. Richard Morrish Associates haven’t recommended planting new Ash or Chestnut trees for more than 5 years now – and we have been looking at other species that can fill the gaps in our countryside – Acer, Alnus, Tilia and less commonly planted genera, such as Ostrya. But it will not be easy to replace Ash and Chestnut. 

Can we avoid a race to the bottom – please?

Most practitioners seem very busy at present – and the race to try to provide the vast amount of new housing government says we need is certainly one reason for that. I understand the cost pressures on developers, but I am worried about the penny pinching that seems to be becoming common – especially in terms of landscape provision. It is a fact that spending some money on landscape provision gives a lot of ‘bang for the buck’. For a relatively small amount of money it can do so much to ‘finish’ a scheme – with obvious marketing and sales benefits.

However, landscape provision is so much more important than that. It was great to hear the feted architect Amanda Levete on Desert Island Discs a few weeks back. She said ‘As our lives become increasingly individualised there has never been a more important time to create outdoor public spaces. Its where relationships are formed, ideas are exchanged – and that leads to progress. We need to make spaces that belong to the public’. Facebook and Twitter cannot replace ‘traditional’ social intercourse. Never is this more important to consider than when creating new residential communities.

Landscape spaces are beneficial in so many ways – whether it is providing safe, comfortable recreation spaces, buffering air pollution, supporting local wildlife or simply providing amenity pleasure. But the basic goal of creating spaces for social exchange and community building is especially important. This is essential if we are going to create safe, healthy, happy and successful communities. Planning and delivering good landscape infrastructure is not a cosmetic optional extra. It is a fundamental element of urban design.

A flexible approach for changing times ...

One of my new year resolutions is to try keep my website updated – my last blog was regrettably a couple of years ago! As we start 2017 there are uncertainties about the future economy, government policy making and the environment in which we work (the impact of new tree diseases is a particular landscape concern). The demand for new housing looks likely to keep the building industry busy in coming years. Regardless of economic conditions, it will be essential to keep standards of environmental design high in the current rush to meet needs. Future generations will not thank us for shoddy buildings or poor residential settings.

Consultant practitioners are going to have to remain flexible, well informed, and responsive to client requirements. This is something we certainly try to do at RMA, and if you are looking at this blog as a prospective client checking what services we provide – please don’t hesitate to give me a ring to chat through your requirements. We are always interested in developing a new approach! 

Aussies Caught Out !

How to beat climate change? I have been thinking for some years if we are going to have milder winters and dry summers maybe some of the tougher Australian plants might have a future in the UK. However the short very cold snaps we have had in recent winters have caught out the Australians. Two years ago the cold virtually wiped out all Cordylines. Im not a great fan of them anyway – and their true home is really the sub-tropics. But this last cold snap in February 2012 has affected much tougher plants – even well established Eucalypts. In my garden I lost my Callistemons and Grevillea even when they were well wrapped up against the cold. Im thinking the relatively warm January (when they all sprouted soft new shoots), combined with a cold so intense it may have frozen the roots – probably did for them. It looks like they may not yet be the panacea for dry summers – unless you want to bring them in every winter!

Seasonal Changes

Many people are talking about the 'early spring' and I have heard a whole range of reports of early flowering – bulbs, primroses, cowslips and all number of garden plants. What I think is even more surprising, and perhaps concerning, is trees and shrubs that have 'skipped' winter completely. I have seen oak and hazel that are still holding on to last years leaves in East Anglia - and they are still green. Ash in my own garden was green until the middle of December. If such mild winters become the norm, will our natives become semi-deciduous? If so I imagine this will impact on a range of phenological phenomena - bud burst, flowering, seed production and especially the relationships with invertebrates and other organisms that interact with trees. We need to monitor how tree and shrub species respond to these changes, as I am sure it will begin to influence management decisions. You can submit sightings to the Woodland Trust 'Natures Calender' site www.naturescalender.org.uk, if you are interested in contributing to a growing record of these seasonal changes.