Planting Under trees
The more organic matter that can be dug into a soil prior to planting the better, as this will allow a greater range of plants to become established.
Carrying out a pH test will establish what kinds of plants you can plant, and adding a balanced slow release fertiliser to the soil will ensure that the plants do not lack for nutrients.
Under a tree canopy can be quite dry due to rainwater being shed to the outer limits of the canopy, therefore it is advisable to apply a mulch in spring before the tree comes into full leaf.
This will conserve moisture that has fallen near the base of the tree when the tree/s was void of leaves during the winter.
Planting out in autumn will also take advantage of the increased rainfall that otherwise would have been shed elsewhere had the tree/s been in full leaf.
If planting under the dense evergreen canopy of conifers it is important to carry out good soil preparation because it is unlikely that the plants will benefit from winter rainfall to the same extent as they would do, had they been planted under deciduous trees.
Plus there is a greater tendency for the soil to be acidic under these conditions.