An old gardening book of mine quotes the owner of a large country estate (one which boasts an impressive collection of rare trees) as saying that he paid: “a shilling for the tree and a pound for the hole,” the pound being the cost of the labour involved to dig a sufficient hole. This quote has always stuck with me, and generally runs through my mind pretty much every time I plant anything larger than a bulb.

Prunus incisa - a pretty flowering cherry that makes an ideal garden tree.

The simple fact is that, once planted, trees and larger shrubs will likely never be moved, and, if all goes well, will remain in place for decades or even centuries to come. Aside from mulching, the only chance that you will ever have to improve the structure of the ground where they will grow is at the time of planting. Bearing that in mind it has to be well worthwhile putting in the time and effort to ensure your spindly sapling will one day grow into a mighty tree (or shrub…)

Although it’s possible, with care, to plant at any time of the year, by far the best seasons are  late autumn and the early spring, when the plants will be dormant and will suffer far less shock than they would in the growing season. The ideal weather is cloudy, cool, windless and most definitely frost-free, so if necessary delay planting until suitable conditions occur.

It was long thought by many that the most important factor in tree planting was the fertilisation of the ground, with the addition of composts, manures and so on. Research has now shown this to be not the case; in fact the fertilisation of your planting hole is actually likely to prove harmful, or even fatal to new trees, the emphasis instead is all on the preparation of the hole itself.

Planting hole preparation - the most important job of all.

Generally speaking the bigger the planting hole the better. The aim is to break up as large an area of soil as possible, not in terms of depth, but rather width, because it’s here that your tree will be making it’s initial forays into it’s new soil.

How big is big? Certainly the planting hole should be considerably larger than the root ball of your new tree and none of the roots should have to be bent or curled to fit in.

It’s important to plant on the same day as you dig the hole as exposure to the elements will kill off many of the beneficial micro-organisms, and in particular the fungi that are present in the soil. Microrrhizal fungi are amongst the most essential members of the subterranean community as far as plants are concerned, and most trees actually derive much of their nutrition not directly from the soil, but rather from these fungi with whom they set up a symbiotic relationship.

Mound planting - to help trees establish on wet ground.

It’s often necessary to be a bit flexible with your planting location too. If you dig down and find standing water or a layer of bedrock, for instance then it’s best to stop right there and consider a new spot.

Having said that trees can be planted in wet sites by mounding soil up above ground level. We’ve taken this approach is a seasonally wet patch of our garden where we have succeeded in establishing a number of Acer palmatum by planting each one on a large mound as much as 60cm above the natural ground level.

In very dry locations you can take the opposite approach and plant in a dip so that any rain-water that happens by will be diverted to the roots of your tree. Be very, very wary, though, of creating a sump that collects water all year round, roots need oxygen as well as water so this is a quick recipe for a drowned plant.

Staking - short and sweet.

Before reaching for the tree, the next step is to consider staking. Unless your new arrival is on the short and stocky side then it’s often necessary to secure by tying to a stake. This makes sure then tree isn’t rocked – or even uprooted – in the wind and will allow it to properly establish at the roots.

Stakes should be short but sturdy – always thicker than the tree itself. It doesn’t matter if the top of the tree moves around (within reason), in fact it promotes thickening of the trunk, and if you stake too high you will end up with a perpetually spindly trunk that may never be able to support itself.

Securely drive the stake into the planting hole on the side of the prevailing wind and make sure you have a good, durable tie to hand – preferably rubber or plastic to minimise rubbing – and long enough to secure the tree but still allow for some movement and flexing, again to encourage strengthening of the trunk.

A rootbound pot-grown tree.

Once the hole is prepared you can unwrap or un-pot your tree or shrub and take a good look at its root system. My experience of planting many thousands of trees and shrubs is that unless the roots are relatively free and open then establishment will be delayed, often for several years. This is particularly key if your tree has been pot-grown.

If the roots are looking bound-together and have spiralled around the inside of the pot, and a gentle shaking and teasing won’t budge them, then the best remedy is to soak or hose away some (or even most) of the compost to try to free the roots without breaking them.

Next mound up a small amount of the top soil that you’ve previously removed into the centre of the planting hole until the tree sits with the base of it’s stem/trunk at the natural surrounding ground level. This level is really crucial. If you plant too deep, with the trunk collar under ground level, then the bark at the base of the tree will almost certainly rot off and the tree will be killed. Too high and the roots will be exposed, severely weakening, and probably destabilising the whole plant.

Then, breaking up all large clumps of soil that you’ve dug out, and crumbling everything into as fine a tilth as possible (again to allow quick and easy root penetration) quickly infill the rest of the planting hole and gently press in with your hands – not with a big stomping, root and air crushing boot! – then water thoroughly to let the soil settle into the hole.

The only material that goes back into the planting hole should be that which came out – or if it’s very poor or stony, other topsoil from as near as possible to the planting hole.

Why not take the opportunity to add lots of juicy well rotted manure or compost to feed the tree? The breaking down of this type of material completely changes the soil chemistry near the tree roots. It robs the soil of oxygen for it’s own decomposition, kills most of the beneficial, but very delicate fungi, and creates excess moisture that leads to root rot. Fertilisers also promote excess shoot and leaf growth, but do nothing for the root system, and will leave the tree with a desperate imbalance that may result in massive die-back as time passes.

Betula nigra - the river birch: well mulched, grass-free and thriving.

Finally it’s important to protect the new tree from competition for water from weeds, and particularly grass – vital if planting in a lawn or field. So once safely planted and staked the planting hole should then be mulched.

We use purpose made mulch mats, which fit flat over the planting hole and give years of protection as they slowly decompose. Well composted bark or garden compost is another, and more attractive alternative for the garden, but be sure to leave the trunk itself mulch-free or you’ll invite basal bark rot once again.

All that then remains is to keep well watered during dry spells, particularly for the first few years, and top up with an annual mulch. Then, sit back and enjoy the fruits of your one-days-labour for many, many years to come.