Propagation by stem cuttings is the most commonly used method to propagate many woody ornamental plants. Stem cuttings of many favorite shrubs are quite easy to root. Typically, stem cuttings of tree species are more difficult to root. However, cuttings from trees such as crape myrtles, some elms, and birches can be rooted.
Stems that are still attached to their parent plant may form roots where they come in contact with a rooting medium. This method of vegetative propagation is generally successful, because water stress is minimized and carbohydrate and mineral nutrient levels are high. The development of roots on a stem while the stem is still attached to the parent plant is called layering. A layer is the rooted stem following detachment (removal) from the parent plant.
Some, but not all, plants can be propagated from just a leaf or a section of a leaf. Leaf cuttings of most plants will not generate a new plant; they usually produce only a few roots or just decay. Because leaf cuttings do not include an axillary bud, they can be used only for plants that are capable of forming adventitious buds. Leaf cuttings are used almost exclusively for propagating some indoor plants. There are several types of leaf cuttings.
This propagation chapter from the Extension Gardener Handbook explains how and why to grow new plants from seed (sexual reproduction) and from cuttings (asexual propagation).
Growing your own transplants from seeds indoors can give you a head start on the growing season. In some cases, it may be the only way to obtain plants of a new or special cultivar (variety) that is not widely available through garden centers. To obtain vigorous plants, start with high-quality seed from a reliable source. Select cultivars which provide the plant size, color (flower, foliage, or fruit), and growth habit you want. Choose cultivars adapted to your area. Many vegetable and flower cultivars are hybrids. They may cost more than open pollinated types, but they usually have more vigor, more uniformity, and better growth than non-hybrids.
Seed dormancy is nature's way of setting a time clock that allows seeds to initiate germination when conditions are normally favorable for germination and survival of the seedlings. For example, dogwoods produce mature seeds in the fall, but conditions are not suitable for seedling survival at that time. Thus, dogwoods have developed a mechanism that keeps the seeds dormant until spring when conditions are favorable for germination, as well as, seedling growth and survival.