Plant propagation can be a wonderfully rewarding activity. You can take great pleasure in knowing you had a hand in a beautiful plant from start to finish. Plant propagation can be done either sexually or asexually. But in order to efficiently help a plant grow and develop you should have at least a basic understanding of horticulture.
Plants are divided into two basic loose categories: angiosperms and gymnosperms. The first of these, angiosperms, are the plants that bear flowers and the leaves are either dicots or monocots. Dicot leaves are those you see on a great many plants such as roses, oak trees or tomatoes, etc. The veins on dicots are netted and their seeds have two cotyledons which are the embryonic seed leaves (already present in the seed) but not the true leaves that develop later. Monocot leaves have veins that run parallel to each other along the length of the leaf and have only one cotyledon. These are the leaves you see on grasses, irises or cannas, etc. Monocots and dicots also differ in their root structures.
Gymnosperms bear cones instead of flowers and have simple leaves like needles such as on pine or cypress trees.
Additionally, plants can be classified according to their growing season, i.e., how long does it take a plant to go through its complete life cycle? A growing season is generally the period of time in which you can grow a plant. Factors that affect when your growing season occurs are climate, elevation, daylight hours, rainfall and temperature. A complete life cycle of a plant is from the germination of the seed to the production of a new seed followed by the death of the plant. Keep in mind that a life cycle is not equal to a calendar year. There are three life cycle categories: annual, biennial and perennial.
Annuals go through their life cycle in one growing season. Here in central Texas I put out my tomatoes in spring and by the time our summer heat arrives and we hit triple digits they will have gone to seed (they don’t like temperatures over 95 ?) so I pull them out. Then I put out new seeds in July and depending on our weather they can last until November. So I can get two growing seasons in one year. Those of you in colder climates will only get one without a greenhouse but your spring plantings may last well into summer. Impatiens get put out after the last frost and will last until the next frost.
Biennials start from seeds and last for two seasons. In their first season they will produce vegetative structures and food storage organs. Using the famous Texas biennial, bluebonnets, as an example, the seeds are put out in October and by winter (first season) you will see an evergreen cluster of leaves or a rosette close to the ground. In spring (second season) they bloom and after several weeks they go to seed and die. The seeds from those plants will start the cycle again the following fall/winter.
The mission of annuals and biennials is to reproduce itself so once it has gone to seed it knows its life cycle is over. To extend the life cycle a little longer you can keep the fruits picked or clip flower heads to make the plant keep on producing. A phenomenon known as bolting is when a biennial passes through both its growing seasons in one season due to climatic conditions, drought or temperature changes. Lettuce is a good example. It requires cooler temperatures but if it is unseasonably hot, it will bolt.
The third life cycle classification is perennials. These plants live more than 2 years and will produce flowers and seeds once the plant is fully mature. Fruit trees can be planted one year but depending on the age of the sapling and the species of the tree, it may be years before it bears fruit. Herbaceous perennials grow and produce flowers and fruit in the spring and summer but will die back each winter to their roots. The plant returns each spring with new growth coming from the root stock of the previous year’s growth. Woody perennials such as trees and shrubs persist as they are all year, losing leaves if it is deciduous in the winter.
Depending on your unique growing conditions and climate, a plant that is a perennial in one area may be treated as an annual in another area. Therefore, if you move from a warmer southern climate to a colder northern climate or vice versa, don’t expect the plants you previously treated as perennials to grow the same. Here in central Texas we can grow tropical plumerias in pots outside to take inside during winter, but on the gulf coast it can be grown in the ground year-round. So you can see that you don’t have to go very far to have completely different growing conditions.
Plant propagation is the process of producing more plants either asexually or sexually. Sexual propagation involves the sexual parts of the plant which are the flowers, fruits, flower buds and seeds. Asexual propagation uses the asexual parts of a plant. These are the vegetative parts such as the roots, stems, buds and leaves and are used to reproduce a plant with cuttings, grafting and other methods.
Here, I will focus on asexual reproduction of a plant. Let’s look further at the vegetative parts of a plant that can be used in asexual reproduction.
We will start with the roots. First, what is the purpose of roots? The root of a plant provides an anchor for the plant. Some roots are shallow and others run deep. They absorb and store water and nutrients to be used by the plant. They can be used to propagate plants, they will adapt to different soils and some roots are edible. The health and vigor of the plant depends on the health of its roots. If you plant a new tree or shrub and the root ball remains in a ball after several weeks you will notice your plant declining or dead already. The roots must be able to spread out in order to perform their job.
There are several types of roots: primary, taproots, fibrous, lateral and secondary. The primary root is the first root you will see on a seedling. It grows out of the bottom of the embryo seed and can either become a taproot or a fibrous root system.
Fibrous roots are the roots you see on those seedling plants you purchased for your garden. The primary root did not elongate into a taproot but rather grew many lateral roots.
A taproot is formed by a primary root that grows deep into the soil and is the central part of the root system and has very little branching or fibrous roots. Many trees have taproots making them difficult to transplant unless the soil is very deep. Growers may undercut the taproot early in the tree’s development, causing the tree to develop a fibrous root system to make it more successful to transplant later. Carrots are edible taproots that must be grown from seed as they can’t be transplanted.
Lateral and secondary roots are those that grow off the primary or other fibrous roots and are usually very small.
Humans and plants both have vascular systems in common. The vascular system of a plant transports water and nutrients to the rest of the plant and can grow either above ground or in the ground. They have three major components: xylem, phloem and cambium.
The xylem transports water and minerals while the phloem transports food to the plant. Depending on whether a plant is a monocot or a dicot determines the arrangement of these components. The cambium is situated between the xylem and the phloem on a dicot and is responsible for the stem’s increase in girth. On a dicot, much like the rings of a tree, the phloem is the outermost ring, near the bark and the xylem is the innermost ring. On a monocot, the xylem and phloem form small bundled pairs throughout the stem. The dicots have a continuous system while the monocots have a discontinuous system. Knowing which system a plant has is important because herbicides are specific to one or the other.
Stems must have buds or leaves. The point on a stem at which a flower or leaf develops is called a node. The space between nodes is called the internode. The length of the internode can be affected by such factors as fertility, light, season, competition and vigor.
There are many different kinds of stems such as crowns, spurs, stolons, rhizomes, tubers, corms and bulbs. Crowns are compressed stems such as on dandelions or African violets. Spurs are those little nubby things on fruit tree branches through which they develop fruit. Stolons grow aboveground such as on strawberries, and are also called runners. Rhizomes are similar to stolons but grow underground such as Bermuda grass and Johnson grass which is why it is so difficult to get rid of. Breaking the rhizome causes it to produce more stems. Tubers are potatoes and the eyes of the potato are actually nodes. Sweet potato on the other hand is a tuberous root which is an underground storage organ. Corms like gladiolus may look like bulbs but do not have fleshy scales like onions or tulips which are bulbs.
The next asexual parts of a plant used in propagation are buds. Buds are the nubby things you see on a branch that has not yet developed into a leaf (leaf bud) or flower (flower bud). A terminal (apical) bud is the bud at the uppermost or tip of a stem. Lateral buds are on the sides of a stem. Auxin is a plant growth hormone that can cause the apical bud to have dominance thereby not allowing the lateral buds to not develop. By snipping the apical bud off you will cause the plant to bush out for a fuller, more compact plant. There are also adventitious buds that may pop up in other areas for whatever reason. If you have ever eaten lettuce, brussel sprouts, broccoli or cabbage you have eaten buds.
The last asexual parts we will cover are the leaves. Everyone knows that leaves are important for photosynthesis. The little stem that attaches the leaf to the stem is the petiole. The base where the petiole attaches to the stem is the node. The bud that may form in the angle formed by the petiole and stem is an axillary bud. Leaves are a key way to identify a plant but also come in a myriad of leaf shapes, margins, arrangements, and blade shapes too numerous to mention here.
A few important leaf parts that you should know are the cuticle, which forms a waxy layer on the epidermis called cutin. It protects the plant from dehydration and the penetration of some diseases. Plants grown in the shade have less cutin than plants grown in the sun. So when you move a plant from the shade to a sunny area, do so gradually so the cutin can build up on the leaves or the plant will die from sunscald or rapid water loss.
If you have ever returned home at the end of the day and noticed your plant’s leaves are all droopy and are tempted to water them. Don’t do it! You are probably over watering if you do. The reason leaves droop at the end of the day is due to the guard cells. These cells have the ability to open and close and their job is to protect the interior of the leaf and regulate the passage of water, oxygen and carbon dioxide. If the day has been hot, the guard cells will close in order to conserve water and keep it in the root system, the vascular system will slow down for the same reason and all this causes the leaves to droop. By morning when it has cooled you will see that the leaves are back to normal. If they are not, THEN water. Watering at night only encourages problems for your plants like fungus so it shouldn’t be done then anyway.
Part II of this article will talk about the ways in which you will be able to propagate at home with little or no money. Which is the best way to do anything if you can.
Cheryl Steins has been gardening for over 20 years and is a Certified Texas Master Gardener with special interest in native plants.
Photo. Delynn Talley