mulching your garden plants protect them from soil erosion and conserves moisture. This gives your plants a chance to develop fine roots while protecting them from drought and other harsh effects of weather on plants. Not mulching your garden plants means you'll be doing more watering of your plants and more basic care that could have been prevented by initial mulching of your garden beds.
Trees & plants generally need watering when the soil surface starts to dry out, especially newly planted trees and plants. Use a garden trowel, or your finger if the soil is loose enough, and dig down a few inches into the soil surrounding the tree or plant. If the soil looks bone dry, you may want to think about watering if no rain is in the forecast.
The best fertilizer of all is a natural or organic fertilizer. If you have no preference or are generally stuck with no choice but a chemical fertilizer, then the best one would obviously be a slow-release fertilizer. These usually last throughout the growing season, meaning less garden work for you. You'll want to choose the best fertilizer for your particular plants. Some plants may require an acid fertilizer, while some plants prefer a more neutral type fertilizer. Follow the directions on the back of the bag of the fertilizer you plan to to use on your trees and plants
Generally, all trees and plants have different ways that they should be cared for. You can't take one rule of plant care and use it for every known plant to man. If only it were that easy. When you obtain a new tree or plant, you really should study up on it to know its likes and dislikes and how you need to care for it properly. A tree or plant that is well taken care of and properly maintained by its owner will better be able to fend off diseases and pests.