How to Propagate Plants?
Plant propagation is simply the process of reproducing plants. Methods range from the easy and natural, such as planting seeds to the high-tech method known as Tissue Culture. There are two types of plant propagation, sexual and asexual.
Sexual reproduction usually takes place in the flowers of a plant, uniting genetic material from two parent sources, the male pollen and the female ovum, and generating a new individual plant or seed. A self-pollinating plant will reproduce with pollen and ovum from the same flower. More often, though, pollen is brought to the flower by the wind or by bees and insects.
Asexual plant propagation is a method of reproducing a plant by coaxing a portion of it into regenerating itself into a new plant. The new plant is genetically identical to its parent. This method usually involves the vegetative portions of a plant, such as roots, leaves, and stems.
Asexual plant propagation can be achieved by:
- Dividing off a section of the plants,
- Creating conditions that induce the division to form roots,
- Planting out the division as a new plant when the root system is large and strong enough.
- Asexual plant propagation also includes methods that take a stem, bud, or leaf from one plant and grafting it onto another plant.
Methods of plant propagation
Sexual Plant Propagation:
The simplest, most common and most widely practiced method of plant propagation is sowing seeds. Our earliest gardening experience has most likely been sowing seeds in our garden bed.
This is by far the most preferred plant propagation method for most gardeners. It is simple, inexpensive, and predictable. However, for many gardeners, especially those in cold winter climates, sowing seeds under cover, either in cold frames or indoors, can provide a welcome jumpstart on the growing season.
Sowing under cover (like a greenhouse), can extend the spring season by growing plants indoors when the garden is still too cold, can make for earlier harvests of spring-sown crops and may allow for succession plantings in the late summer or fall.
Asexual Plant Propagation:
Methods of asexual plant propagation vary widely, and fall into four broad divisions: Rooted Materials, Forced Rooting, Grafting and Tissue Culture. Rooted Materials include plant parts with roots or root-like characteristics. Bulbs, corms, rhizomes, and runners are root-like plant parts that readily grow when planted out individually. This category also includes plant propagation by division, which is the sectioning of a plant into two or more parts, each with enough intact root systems to be able to grow as an individual plant. Rhubarb, a perennial vegetable, is often reproduced by dividing the fleshy rhizomes.
Forced rooting includes two common but very different methods of asexual plant propagation. Cuttings use the tip of a stem or branch and by creating conditions that are favorable, coax the cut stem to grow roots. The four main types of stem cuttings are herbaceous, softwood, semi-hardwood, and hardwood. These terms reflect the growth stage of the stock plant, which is one of the most important factors influencing whether or not cuttings will root. The easiest and most well-known type of cutting is herbaceous cuttings, which use a supple green cutting, most often from a vigorous spreading plant that will root easily, such as mint.
The other forced rooting method is called layering. This is a variation of a natural process in which low-hanging branches that lie on the ground or are partially buried grow roots. Layering simply manipulates this natural phenomenon to induce rooting when we wish it to occur, by creating a wound on a stem, burying it and waiting for it to root.
Grafting is a plant propagation method that takes a stem from one plant and adds it onto the stem of another plant. The aim of this procedure is often to create a plant top with one function such as bearing copious amounts of fruit and a root system that is vigorous enough to allow the top portion to achieve its function. Seldom used in the vegetable garden, grafting is common for fruit trees such as apples which combines a strong, time-tested, size-specific rootstalk with a trunk and branch system specifically bred for fruit production and disease-resistance.
Plant tissue culture relies on the fact that many plant cells have the ability, known as totipotency, to regenerate a whole plant. Single cells, protoplasts (cell material without cell walls), pieces of leaves, or roots can often be used to generate a new plant on culture media given the required plant hormones and nutrients. Modern tissue culture is a laboratory procedure performed under sterile conditions and is definitely NOT an organic gardening technique. Despite that, tissue culture does serve a useful ecological function by allowing the preservation and reproduction of rare and endangered plant species that cannot reproduce naturally, either because of habitat loss or the scarcity.
In plant propagation, you will have the best results if you grow seeds or cuttings in a medium specifically tailored to your needs.
Known as growing media, these are soil-like mixtures in which you sow your seeds, place your cuttings or plant your divisions.
Contrary to what you might think, these are NOT soils, and common garden soil, or sifted compost are not the best media in which to start plants. This is because seedlings, cuttings, and young plants have very different needs than plants with developed root systems. An ideal growing medium has five essential qualities designed to promote vigorous root growth:
- It is moisture retentive, but does not easily become oversaturated
- Llight, fluffy, and well aerated so tender roots can grow without damage
- It contains specific nutrients in adequate amounts to support root and stem tissue generation
- It is consistently uniform in texture, so that plants growth will be easy and predictable
- Pathogens free
There are four major groups of growing media, each with a targeted purpose; Seeding mixes, Potting mixes, Rooting mixes, and Multi-Purpose mixes:
- A seeding mix is used to germinate seeds in containers or under cover.
- Potting mixes are used in pots to root divisions or grow plants with developed root systems.
- A rooting mixes is formulated to induce root growth in cuttings.
- Finally, a multi-purpose mix is a growing medium intended to provide two or more of the functions of the single-purpose mixes listed above.
Sowing in the garden bed
Sowing seeds directly into the garden bed is easily the most popular method of plant propagation. It’s simple and easy, and produces great results –provided it is done correctly.
You will have the best results if you provide your tender seedlings with the conditions that they need. Successful seed germination depends upon the balance of four main elements: The vitality of the seed itself, appropriate air temperature, soil temperature, and a specific amount of moisture.
The vigor and condition of the seed is critical for becoming a new plant. Fresh seeds and seeds stored under the proper cool and dry conditions will be at their best.
Most vegetable seeds are viable for up to five years under optimum storage conditions. However, as a seed ages fewer will remain viable, so fewer and fewer will sprout as time goes on. Purchase new seed from a reputable supplier, and store them appropriately. If you do not save seed, plan your garden so that you will not have any seed leftover for the next year.
Air temperature and soil temperature in the garden are functions of the weather. If air or soil is too cool, or too warm, seeds will not germinate.
For most of the country, it is too cold in early spring to sow directly in your garden. You will need to wait until the conditions are right for germination in your locale or buy a greenhouse.
By contrast, it is often too hot in much of the country to sow seeds in mid-summer.
The element over which you have the most control is the condition of your garden bed. Remember that seeds are like embryos and seedlings are like infants, tender and soft and needing special conditions to thrive. Create a seedbed in your garden where you plan on sowing seeds. It should have the same five characteristics as any growing medium. A simple method is to modify the top few inches of you regular garden soil into a seedbed. As your seedlings put out true roots they will grow down into your garden soil.
Sowing under cover
Where winters are long and spring comes late, sowing seeds under cover is a great way to get a jump start on your spring gardening.
By germinating seeds and growing garden plants indoors, you will have small and healthy starts to plant into the garden when the danger of frost abates.
This method of placing a relatively mature plant into the garden at a relatively early date will produce earlier harvests. Careful timing may allow a successive crop where sowing seeds directly in the garden bed may only allow one crop.
With planning this method can also be used to replace plants as they are harvested, so that you might have two crops in the same amount of time as one crop traditionally planted.
For example, if you have a new lettuce start ready to plant, you can replace it in the space where you just harvested a mature head of lettuce.
Sowing under cover includes planting seeds into a seed tray, in pots, under a hoophouse, in a greenhouse, in a coldframe, or on a windowsill indoors.
You will need:
- An appropriate growing medium
- A pot or container,
- Optimal conditions of light, water, and temperature.
Saving seeds from the plants that you grow is an economical and practical way to garden, especially if you are planning and growing for the long term. Since seeds are a product of sexual reproduction, they contain genetic traits of both parents.
If you have planted an open-pollinating variety, then seed saving can be as simple as collecting seed from the earliest and most vigorous fruits of the plant whose seeds you wish to save. If you have planted a hybrid variety, it is probably not worth saving seeds, since hybridized plants do not grow ‘true’.
An open-pollinated plant will reliably retain the same similar characteristics from parent to offspring, but hybrids do not. A seed grown from a hybrid will only on occasion show the desired characteristics or its parent, and will more often revert to the characteristics of one of its grandparents instead.
If you planning on seed saving, you will want to plan your garden accordingly, and you will need to select seed deliberately. Select seeds for health and purity. Save seeds only from the plants that have the desired characteristics.
Cull plants that have undesired characteristics before they set seed. A dwarfed pea plant among vines, or a bean plant with the misshapen pods should be pulled. They are probably the result of cross-pollination by insects or the wind and will not produce seeds that grow ‘true’.
Save seed only from your most vigorous and healthy plants. In this way you are augmenting nature by favoring the strongest and best seeds over weaker individuals. Never take seed from a plant that has disease or was stunted by insects, soil deficiencies, or environmental conditions. These will not thrive and may carry over pathogens into the next growing season.
Biodiversity & heirloom varieties
Humans have been growing for millennia, and over that time have developed hundreds of thousands of cultivars.
By selectively breeding for adaptation to climate, to produce larger and more reliable crops, or resist pestilence, many of these new varieties do not even resemble their primitive parents.
All of the new varieties that humans have created, up to the last few centuries, have been open-pollinating varieties, which grow ‘true’ to the parents. Since the decoding of genetics by Gregor Mendel, hybrid varieties have become more and more common.
Currently, distribution of seed for home and commercial gardening and farming relies upon a system of commercial seed producers.
Out of the many varieties available seed catalogs can only offer a handful of varieties, usually the most popular or the most trendy.
As a result, many older or less commercial cultivars have been dropped from sale, and may disappear altogether. Many of these endangered cultivars have characteristics well suited to small gardens or a particular climate. It is in everybody’s interest to preserve these heirloom varieties.
The broader the choice of cultivars, the more genetic material is represented.
The broader the available genetic material available, the more stable is the garden ecosystem. This because the garden is not a natural ecosystem with natural checks and balances.
It is instead a managed ecosystem, in which things can quickly get out-of-balance. Organic gardening seeks to enhance natural systems, and one way to do that is to broaden the scope of genetic material in the garden by growing a good mix of cultivars, with open-pollinating types, heirlooms, and hybrids. In this way, if a disease strikes the garden the likelihood that all your plants are affected is minimized.