By the very nature of the way they grow, Bonsai trees have a limited source of nutrients.
When re-potting, they need a compost that provides the correct balance of drainage, water retention and aeration needed to develop a healthy root structure.
GETTING STARTED: Bonsai can be developed from seeds or cuttings, layering, air layering, stump or mound layering, from young trees or from naturally occurring stunted trees. A good time to find suitable plants is to search around the garden or hedgerows in summer when many self-sown seedlings will have pushed their way up through the soil and can easily be lifted and re-potted. You can begin however by choosing suitable older subjects and therefore larger and more developed. A trained eye with an aptitude for possible bonsai material can spot likely young plants on visits to the nurseries and Garden Centres.
SOIL: The first thing you will need is the most important ingredient to grow a plant: dirt. This can be obtained by going out behind your house with a shovel. If you are looking for better results, picking up some seed starting soil from your local gardening store will increase success. Seeds are susceptible to diseases that are found regularly in outdoor soil. Seed starting soil has been baked at a high temperature to become a sterile soil, without the added bacteria. If you are growing a small amount of seeds, backyard dirt is fine. A few of the seeds are likely to survive regardless of what soil you use.
WATERING: Another very important care consideration is the correct amount of watering. You must ensure that the bonsai tree is in a sufficiently big enough pot to hold enough moisture to support the tree. Your bonsai should never be left to completely dry out. At the other extreme, a bonsai tree can suffer if it is over-watered or left soaking in a pool of water. Special care when watering is needed if your tree is root-bound or if it is exposed to the sun and wind.
PRUNING: Bonsai are kept small and trained by pruning shoots and roots, by periodic re-potting, and by pinching off new growth. Mature looking bonsai plants are not necessarily old. Pruning and pinching foliage and new growth to train and shape the plant create the illusion of age. Aluminium wire can be temporarily used to reposition or bend a branch or trunk, but it should be removed before it scars or cuts into the branch. Bonsai, which are grown for their blossom, must be pinched judiciously or there may be few if any flowers. In such cases pinching is carried out after the flowers have faded.