Seedlings, cuttings and transplants
The early stages of a plant’s life are a critical time. Like children, those raised in a healthy and nourishing environment grow up to become strong and productive; those raised in threatening and impoverished environments are always at a disadvantage and rarely mature to fulfill their true potential as adults. Vigorous, healthy seedlings develop greater resistance to disease and insect infestations and promise faster growth and higher yields.
The gardener is like a mother to the young plant. This is the stage when carelessness, inconsistency and indifference will result in a poor crop, no matter how much attention is lavished on the plant later on. A nurturing gardener anticipates the plants’ needs and avoids letting problems develop. By the time you can see the problem, damage has already occurred. The objective is to avoid problems, not seeking remedies after they appear.
The process of birth in plants– germination–requires a specific set of environmental conditions that differ from those found in the typical greenhouse or grow room. In the wild, plant varieties have adapted to local conditions, soils, rainfall, soil temperature, air temperature and available light. It is these conditions that define the natural range of wild plants. In the greenhouse or grow room, it is the gardener who creates and maintains those conditions suitable to the development of the embryonic plant into a healthy, thriving adult.
Seeds are usually started in flats containing a sterile soil or “soilless” mix, typically consisting of peat and vermiculite. Small rockwool or foam cubes are also commonly used. As in any maternity ward, cleanliness is essential. Mixes containing soil can be sterilized by heating to 140°F (60°C) for 30 minutes. Tools and flats can be rubbed down with a 10 percent bleach solution or rubbing alcohol, then rinsed.
Root zone temperature control is especially important for starting seeds and during the early stages when plants are easily damaged. During cooler months, use heating mats or cables under the flats so that the young roots are held at a constant temperature, between 70° and 80° (21°-27° C) for most plant varieties. A clear dome or cover over the flat will aid in maintaining warmth and keep humidity high.
Air temperature is also important, as is proper ventilation. A gentle flow of air through the seedlings helps young plants “breathe” and is especially important in damp environments to avoid infection, especially from fungal pathogens. As the seedlings emerge, it may be necessary to thin out dense plantings to improve ventilation. Use a pair of sharp scissors to trim the tops off plants to avoid disturbing the roots. Excesses of heat or cold are detrimental to delicate young plants. In hot and humid environments, it may be necessary to introduce cool or dehumidified air.
Young plants cannot tolerate excessive light intensities. In the greenhouse, shade cloth is used to reduce light. Artificial lighting is commonly used when seedlings are started indoors where temperature, humidity and ventilation are easier to control. Fluorescent light is ideal for starting seedlings and cuttings. Full spectrum lights should be placed close to the young plants until they have developed sufficiently for transplantation. The farther the light source is from the plant, the lower the light intensity. Generally, 6 to 18 inches above the tops of the plants is appropriate with fluorescent light.
Correct moisture is difficult to define. Too much moisture will cause seeds and delicate young roots to rot. Inadequate moisture will cause drying of the roots. Both conditions can be fatal, or at least damaging to the plant’s long term potential.
One way to control moisture is to cycle between thorough, but gentle, waterings and periods of reduced moisture. The idea is to constantly provide sufficient moisture for delicate roots while at the same time allowing oxygen-rich air to penetrate the rooting medium between waterings. This will provide the plant with the necessary moisture while creating an environment that is inhospitable to pathogens that need high moisture levels to survive. Careful monitoring is the key; at no time should the rooting medium be allow to dry out completely.
Starting plants from cuttings, a method widely used by commercial growers, is becoming more popular with home gardeners. Starting plants from cuttings, also called clones, allows the grower to circumvent the process of sexual reproduction– flower, fruit and seed–and produce individual plants directly from a mature adult.
Plants generated using asexual propagation methods assure the grower of greater genetic consistency. Disease resistance, flower color, fragrance, fruit characteristics and yield are much more certain when plants are generated from cuttings. In addition, cuttings often develop more rapidly than plants started from seed.
Many types of plants can be easily started from cuttings. Other plants, conifers and palms, for example, are far more difficult. Hydroponic methods and equipment have proven to be effective tools in producing plants from cuttings.
Oxygen-intensive systems, such as Aeroponic systems in which plant roots are bathed in a fine nutrient mist, have induced root formation in plants thought nearly impossible to clone. A hybrid aero-hydroponic system developed at Ein-Gedi Israel has been used successfully to propagate pistachio and some conifers from cuttings, notoriously difficult to propagate.
Regardless of the method used it is important to take cuttings from healthy uninfected donor stock. In the nursery industry it is common to maintain a special stock of donor or “mother” plants from which to take cuttings. Some of the worst infestations of plant diseases such as Pythium and fusarium can be traced back to infected donor stock. A single infected cutting can spread disease leading to a complete crop loss.
A good mother plant should be disease-free and robust. Poor growth in the absence of any discernible disease can be a sign of genetic weakness that will be passed on through any cuttings. Cuttings taken from wild stock lack the certainty found with cultivated donors. In addition, wild plants may pass on diseases that can decimate the cultivated plants in your collection. If you are unsure of the health of your donor stock, isolate the cuttings and monitor for signs of trouble.
Cuttings are made from the vegetative parts of the donor plant. Stems, leaves and roots are the most common tissue sources for propagation. Bulbs, corms, tubers and rhizomes are also used for propagating some plant varieties.
Stem cuttings are classified as herbaceous, softwood and hardwood. Herbaceous cuttings are generally the fastest and easiest to propagate, hardwood the slowest and most difficult. Herbaceous plants include chrysanthemum, geranium, carnation, coleus and mint. Hardwoods include rose, rhododendron, azalea, wisteria, privet, grape and olive.
Some plants can be propagated from leaf cuttings, such as African violets and some begonias. Others like kiwi, trumpet vine, fig, apple, some roses, blackberry and raspberry can be generated from root cuttings. Root cuttings can pass on fungal, bacterial or viral diseases as a result of infected soil attached to the root tissue. If possible, isolate root cuttings from other starts.
Because the process is simpler and more reliable most hobby gardeners use stem cuttings. It is essential to use very sharp pruning shears or a sharp blade to take cuttings. A dull instrument will crush basal tissue, the delicate system of canals within the stem that carry moisture and nutrients up the branch. Perhaps the best instrument for taking cuttings is a single edged razor blade. Experienced growers will clean the blade with alcohol between plants to avoid spreading disease from one donor plant to another, a cautionary approach since experienced growers understand the importance of not spreading disease organisms through carelessness. Make cuts just below a leaf node and remove the first set of leaves. This is where the first roots usually appear. Be sure to keep several sets of leaves above the root zone. Remember to clean the cutting instrument with an alcohol wipe between cuts to prevent the spread of infection.
In some cases it is helpful to wound the cutting at the base where the first roots will form. Lightly scrape the bottom half inch or so of each side of the cutting. Don’t get too carried away, avoid penetrating below the bark and into the woody part of the cutting. The objective is to slightly disrupt surface tissue.
Cuttings are usually treated with hormones to stimulate faster root development and a stronger root structure. Hormone treatments are marketed as “quick-dip” method, “dilute soaking” method, or the powder treatment. All of these methods have their advocates, but the important thing is to follow the directions carefully and not to overdo it. Technically speaking, hormone treatments are poisons; some commercial preparations contain powerful fungicides to prevent infection. Avoid skin contact with these products. The powdered hormones are especially hazardous if the powder becomes airborne and is inhaled. Treated cuttings can be placed into small rockwool or foam cubes, into a soilless mix such as coconut fiber or directly into a hydroponic system. The end of the cutting should be kept moist at all times.
Once the roots begin to emerge and new growth begins, the cuttings are ready to transplant. With seedlings, wait until the first true leaves (the second set to develop) are fully formed before transplanting. Transplants are the toddlers of the plant world–with all of the drive needed to grow into mature productive adults, but still in need of tender loving care. Transplanting is a pivotal event in a young plant’s life. Done correctly and carefully it can give your cutting or seedling the space it needs to get off to a good start. Done poorly, it can stunt a plant for life or kill it outright.
In the greenhouse, choose a cloudy day for transplanting or place your transplants in a shaded location for a day or two after transplanting. Bright light and extremes in temperature can cause or aggravate transplant shock. Your starting mix should be just dry enough to crumble easily in your hands, but not too dry, before attempting to remove seedlings or cuttings from the flat. Working slowly and gently, separate the plant roots and remove, one at a time, from the flat. Hold the seedling or cutting by its stem with the root mass hanging in the container into which it is to be planted. Gently add the hydroponic medium or soil, handful by handful, until the roots are surrounded and the plant is supported. A wooden or plastic stake is sometimes helpful if a plant wants to fall over. The keyword here is gently. Roots have tiny, practically invisible root hairs which are easily damaged. Research has shown that damaged roots are an open doorway for many diseases, Pythium for example.
In hydroponic systems, run a very mild balanced nutrient solution (300 to 500 ppm) for the first week following transplanting. Use distilled or purified water to mix this first application of nutrient. Nutrient strength can be increased when the plant has recovered from the transplant experience and begins to grow. Nutrient temperatures should be maintained in the range of 65 to 80° (18° – 27° C). Avoid extremes of light, temperature and humidity and protect recent transplants from wind and drafts. A gentle “hospital” environment should be maintained until the plant is fully recovered.
In most cases there will be no transplant shock and the plant will begin to grow quickly. Gentle handling and consistent care in the early stages of life will result in healthier, more productive plants later on. Once you have raised a healthy young plant from seedling or cutting, your plant is ready to enter its teenage period. Small and immature, yet strong and vigorous, your plant will charge forward toward maturity and its productive period. From the moment that the seed germinated or the cutting generated roots, your plant is genetically encoded to fulfill a single purpose, to reproduce and generate seed for the next generation. As a skilled grower you can guide your plants to their destiny by providing a nurturing, stimulating and protective environment. Remove barriers to the plants growth and it will fulfill its destiny, richly rewarding you with fresh, high quality produce.