Chapter 20

Vegetative Plant Propagation

Plant Propagation by Cuttings

Many types of plants, both woody and herbaceous, are propagated by cuttings. A cutting is a vegetative plant part severed from the parent plant that ultimately will form a whole new plant. Plant species differ when it comes to the optimum time to take cuttings (hardwood, semi-hardwood and softwood) as well as the plant material (leaf, leaf-bud, stem and root). Some plant cuttings root anytime during the growing season while other plants only root from cuttings taken during a particular point in the growing season. Cuttings can be collected from mother plants or special donor plants can be cultured in the nursery. It is important to sanitize the sharp knife or razor blade with rubbing alcohol or a mixture of 1 part bleach and 9 parts water to prevent transmitting diseases from infected plant parts to healthy ones. Remove flowers and flower buds from the cutting to allow it to use its energy and stored carbohydrates for root and shoot formation rather than fruit and seed production. To hasten rooting, to increase the number of roots or to obtain uniform rooting (except on soft, fleshy stems), dip the cut tip in rooting hormone such as IAA, IBA or NAA to improve the rooting percentage and encourage more vigorous roots.  It is important to choose the correct rooting medium to get optimum rooting in the shortest time. In general, the rooting medium should be sterile, low in fertility, well drained and able to retain enough moisture to prevent water stress. Use coarse sand, vermiculite, soil or a mixture of peat and perlite. Moisten the medium before inserting cuttings, and keep it evenly moist while cuttings are rooting and forming new shoots. Place stem and leaf cuttings in bright, but indirect, light. Root cuttings can be kept in the dark until new shoots appear.

Leaf Cuttings

Leaf cuttings are used almost exclusively for a few indoor plants (See Figure 20.1). The four types of leaf cuttings are as follows: 1) whole leaf with petiole, 2) whole leaf without petiole, 3) split vein, and leaf section. Leaf cuttings first must form roots and later shoots. The leaves can be placed on top of the rooting medium or can be inserted into the medium.

Stem Cuttings

Many plant species are propagated by stem cuttings. For some plants, you can take cuttings at any time of the year. Stem cuttings of many woody plants must be taken in the fall or in the dormant season. There are two types of stem cuttings, depending on the location of the cut. They are discussed below.

Stem-Tip Cuttings

A common method of propagating plants is to take stem tip or terminal cuttings (See Figure 20.2). A wide range of plants can be propagated by stem tip cuttings, including herbaceous plants, such as chrysanthemums and carnations, soft wood plants, semi-hardwood, and hardwood plants. Detach a 2- to 6-inch (5 to 15 cm) piece of stem that includes the terminal bud.

Stem Cuttings

A section of the stem without leaves, but with dormant buds, is rooted in a porous growing medium (See Figure 20.3). This type of cutting is popular to use with plants that exhibit a cane-type of growth, such as dieffenbachia (dumb cane). Cuttings should be 4 to 6 inches (10 to 15 cm) in length and taken from vigorous, healthy plants

Root Cuttings

Root cuttings usually are taken from 2- to 3-year-old plants during their dormant season, when they have a large carbohydrate supply. Root cuttings of some species produce new shoots, which then form their own root systems. Other plants develop root systems from the cuttings before producing new shoots.

Cutting Preparation

While preparing cuttings, it is important to keep the work area clean. Use sharp, well-maintained shears and knives to make clean cuts and disinfect them often to reduce the possible spread of disease. Preparing cuttings standardizes their size and shape, promotes side shoots, and eliminates shoot tips that often die back.

Wounding Cuttings

Wounding, used on species that are difficult to root, increases rooting percentages and improves the quantity and quality of roots produced. Wounding exposes more cells to rooting hormone, encourages callus formation, and, in some cases, removes thick woody tissue that can be a barrier to root formation.

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