Why planting trees is no guarantee of greening

Design: Function before form

Every tree that ends up in the ground starts life on the drawing board. The designer fills the green space, thinking about the long-term vision, but most importantly, nailing down what those trees need to do. Trees can be so much more than just lovely. They trap particulate matter, provide shade, cool things down, boost biodiversity, and help store water. Lately, we also value them for capturing carbon as long as they live.

In my ideal world, the designer would design the space and function before picking a species. The first question: what’s this tree actually supposed to do? Why do we even want a tree here? The right tree, in the right place, for the right reason. 

Platanus in an endless growing space, Gent Belgium

You can also factor in the intended lifespan based on available growing space and realistic future prospects. Meanwhile, there’s a parallel craft: how do you design the growing spot, and which assortment of trees fits the brief? Here, too, age expectations must be checked. That calls for specialists. A designer who tries to do everything themselves is like one of those old radio-cassette players with a built-in turntable. It has everything, but nothing works properly.

Growing space: Stop half bakes tinkering

Ideally, trees grow in open soil. If that’s not possible, always put quality of growth first for the full intended lifespan. I’m getting less and less excited about “stuctural” soil solutions that only work on paper. Especially with tree granulates, I see too few healthy regrowths. Not because the material itself is bad, but because it’s often messed up during construction on site.

Platanus in tree granulate with mainly highly developed rooting

Here’s the crux: contract formation. The civil engineer needs to compact the ground so the pavement won’t sag. The tree ends up in another contract. The result? A tree that survives the initial phase, then quickly gets stuck in an impenetrable growing pit. Roots crawl just under the hard surface, lifting up pavement, roots get chopped off, and after a few years the tree, still being a youngster, starts going backwards. I call that failure; a young tree should not be shrinking back. Period.

With simple measures, like using an Light Weight Deflecto meter during installation, you can easily prevent dense soil during construction. But you’ve got to want to, and actually do it. Protect growing locations in policy. Map out rootable space digitally. If a site could offer endless growing room, claim it and fix it in your zoning plan. If you must tinker, go for solutions that mimic nature as closely as possible. A well-designed “tree bunker” is the closest you’ll get to forest soil as long as you keep the natural nutrient cycle ticking.

Poor results? Blame the nursery

That’s just too convenient. To guarantee quality delivered you have a duty to inspect the tree on arrival. Quality control here is tricky, since you’re working within nature’s margins. It’s not as clear-cut as buying a car. Yet I rarely see truly rubbish nursery trees. Most problems crop up later, due to poor planting work.

Nurseries have a vested interest in quality. A tree isn’t an industrial product. It takes six years or more to grow one, so a long-term customer relationship makes sense. You can even arrange contract growing for regular supply. If you want rare species or weird quantities, well don’t be shocked when you get weird answers. And if you always go for the cheapest, you’ll get the quality you pay for.

Populus size 12-14 at a tree nursery where exceeding the trunk-length ratio 1-35 is a real risk

Nursery experts know their young trees like the back of their hand. Arborists see what happens in later stages and can use that knowledge to pick the right species. Especially real crown volumes arborists know those inside out. Get those experts together, and you’ll come up with a realistic requirements species list that’s gold for the designer.

One requirement I’d love to add to nursery contracts is tougher rules against unwanted hitchhiking treeguests. The bacterium Xylella fastidiosa, rife in southern Europe and a threat to over 300 tree and plant species #LINK# (sometimes with dramatic consequences), is a real risk. Given all the trading with southern Europe, I say make it a rule: trees must have spent at least three growing seasons in your country before delivery.

Contract formation: Pay for growth, not numbers

This might be the biggest key to success. A contract specifying “plant 100 trees” encourages exactly that;100 trees in, job done. A contract saying “100 trees must establish and keep growing” changes everything. It’s a challenge for the serial planters, a golden opportunity for the quality crowd.

The accompanying conditions might be:

• At least three years of aftercare (five in cities, if you want to get serious);
•           A measurable result: yearly increase in average shoot length, including the top, per tree;
•          Restart the aftercare period if replacements are needed.

Put the risk where it belongs. It’s not a punishment for contractors, but a chance to show real expertise. And please, add to the contract that any aids and (plastic) watering collars are removed at handover. Better yet, set requirements for eco-friendly planting, to cut down on plastic rubbish.

Planting: Planting trees isn't the same as burying them

This might be the number one disaster factor. Trees are staggeringly often planted far too deep. Honestly, the sandier the soil and the more the planter’s background is in landscaping, the deeper the tree goes. Lindens are almost indestructible unless you plant them ten centimetres too deep. Then the result is guaranteed: a dead tree.

Clearly too deeply planted Prunus

Don’t plant in waterlogged soil. Don’t work in the rain. Only dig over growing places if needed for compaction, and stay above the highest groundwater level. Ideally, improve soil quality months before planting. Fresh compost doesn’t belong in the planting hole. Green manure available? Brilliant. That’s an investment in soil life. Pruning during planting is a touchy issue. In my experience, reducing the evaporative surface of fast-growing species and oaks boosts establishment. The trick is not to chop the crowns open, but, just like in the nursery, trim leaf volume from the outside by up to 25%. An intriguing field study amd nursery experience backs this up.

Aftercare: Technology helps, attention saves

Aftercare isn’t an afterthought. And sensors are no substitute for good horticulture. A moisture sensor tells you what’s happening at one spot. That’s it. Relying blindly on data without looking in the field is a great way to miss the obvious. Good aftercare means looking, feeling, sniffing. Does the tree look healthy? Can you squeeze a soil ball without water pouring out? Does the soil smell like a forest floor? Then you’re on the right track. Yellowing leaves, droopy top, swampy-smelling soil? Trouble ahead.

Aftercare in London carried out by citizens is great for engagement, requires proper communication and control

Watering should be demand driven. Not by the calendar, not by habit, not because the contract says so. Private owners have a tendency to love their trees to death by running the sprinkler every day.

End result: YES, IT CAN BE DONE

Internationally, failure rates of 25% to even 50% years are accepted. Shocking, if you ask me. In my experience, failure rates are about 2% with proper planting. The difference isn’t luck, it’s choices: design, growing site, contracts, planting, and aftercare.

If we’re braver in the early stages and put the risk of failure where it belongs, I’m convinced we’ll not only plant more trees, but far more importantly see many more of them grow.