Melbourne’s famously variable climate is never more obvious than in Spring. Cool and hot days can be sprinkled liberally through the month. As the weather warms up, plants will become more active, and their water needs increase considerably. Planting trees in Spring means that just as the tree is adjusting to a new environment just as it’s water needs are increasing. Here are some things worth remembering:
1. Give the pot a good soaking before you plant. Not just a quick surface water, but a good, deep drink. If possible, plunge the pot into a bucket of water, and let it get completely saturated. This is important because, up until it is planted, the tree will have been surface watered only so the centre and lower part of the root ball may not be damp, and if it goes into the ground with dry soil around the roots subsequent surface watering might not reach these parts after planting.
2. Make sure that you water the hole before you plant the tree. A crucial step that is often overlooked is ensuring that the soil the tree is going into is at least as wet as the soil around the tree. There are several reasons for this. Firstly, the porosity of the soil in the ground is likely to be different from the soil in the pot. This means that when the pot soil touches the ground soil, the difference in porosity will mean that water will be drawn from the wetter soil to the drier soil. This also helps avoid another common problem, which is that the surface of the soil in the pot can be less permeable than the soil in the garden. This is caused by a build up of roots in the upper part of the pot. This can lead to water run-off when watered from above.
3. Scratching out roots is very important. There is a bit of an art to this, as usually the roots at the edge of the root-ball are the finer feeding roots, and are therefore most delicate and also most important to the tree. It’s important to free them up, so that they start growing outwards immediately, and that they are surrounded by fresh, moist soil. However, scratching out overly-aggressively can lead to a loss of important new roots. This is also a time to do some root pruning it required. Large roots at the edge of the root ball can be pruned back a little to encourage the growth of new, outward growing roots.
4. If planting into heavy or clay soils, make sure that the bottom of the hole is dug in such a way that the centre of the hole is the highest point at the bottom, with a slope away from the centre. This can then be leveled by filling the bottom of the hole using good quality mix. The reason for this is to avoid creating a ‘sump’, where water can collect and sit, rotting the roots. This sometimes happens when a hedge is put in, and a single trench is dug for the hedge. Because the water will travel horizontally in heavy soils, pools can form at the lowest point of the trench. This can mean that only one tree in a hedge dies, because it has been unfortunate enough to be sited at the point where the water collects.
5. Once planted, make sure that the gap between the hole is filled evenly with mix, and tamped-down gently to avoid any air-pockets forming. Then, its time to give the tree another good soaking, making sure that the entire area around the tree, including the root ball and the new soil, is well watered.
6. If you are using a mulch, make sure it is damp when applied, and apply it to damp soil. Dried out mulch can wick moisture away from newly planted trees.
7. Monitor watering and weather until the trees settle in. When planting trees, the environment around the roots is radically altered. Where there was once an impervious barrier, there is now new soil. Moisture and gas levels will vary significantly, and for a tree putting on new growth, this potentially places extra strains on the trees just as it is entering its most active growth season.