A hands-on day at Kew, with members of the International Dendrology Society, to learn from the curator of the country’s most important tree collection. You might think that growing trees was a skill long since done and dusted. Not on Tony Kirkham’s watch. From the pot to the hole, the compost to the mulch, the label to the stake, the guard to the watering regime, the planting to the pruning, every practice is reviewed and questioned. The result: many happy young trees, and a day of engrossing interest.
Micorrhyza come high on Tony’s agenda. He adds them, in the form of a product called Transplant 1-Step, to every planting hole. He even waters them on to the roots of established trees that need encouragement. His thinking is that intimate and instant contact between roots and soil is paramount, and micorrhyza ensure that contact. He favours square planting pits, scarcely deeper than the root balls they are to accommodate but four times as wide. Round holes, he believes, only encourage roots to circle. Does a root know it has hit a straight wall rather than a curved one? Apparently it does. And Kirkham doesn’t add organic matter; just backfills with the mineral soil. But then Kew is on sand. He doesn’t add fertilizer when he plants a tree, either. It kills micorrhyza. Bone meal perhaps in the second year, scattered on the surface. By then, he reckons, the roots will have filled the pit and be foraging in the surrounding undug ground.
There was much more, from ‘Airpots’ (and planting out as young as possible) to a system for decompacting the soil under mature trees by forcing in compressed air. (Again, I felt that what works in Kew’s sand would get stuck in Essex clay.) The entire root area is then treated with glyphosate to kill the grass and mulched with wood chippings, preferably of the same species of tree.
To answer the problem of watering young trees he showed us a new American device I shall certainly look for. It is simply a bag with a leaky bottom that holds 20 gallons of water. You fasten it round the trunk and it leaks very slowly where the water does most good. It is called a Tree-gator, but never mind.