If you need help with identification, consult a knowledgeable nurseryman, native plant society or local garden club. In general, woodland plants are found growing in well drained, loose textured soils rich in organic matter. The best way to provide this environment is with a mulch of rich organic matter. If your soil is very poor, consider applying a four to six inch layer of compost to the entire area and tilling it in as deep as possible.
Mulch depth can vary from three to six inches.
Keep the material about six inches away from the trunks of trees and shrubs to encourage air circulation and discourage rodents. A rich mulch like compost can be topped with a decorative layer of chipped bark. If you contract this work, be sure to get local references and check the firm's insurance. If you have any comments or suggestions, feel free to contact me. The bottom of the trench should slope to the left or right, depending on the overall grade of the area - you want to drain the water away.