Plant Propagation from Seed
Greenhouse Transplant Production
Seedlings are ready for transplanting when their first or second true leaves have developed (See Figure 24.10). The first (lowest) set of leaves typically seen on aseedling is the seed leaves or cotyledons. These leaves are usually a different shape from the true leaves. They serve as a source of food for the young seedling. True leaves develop after the seed leaves and have the shape of the mature plant's leaves. Seedlings should be transplanted as soon as they reach the first or second true leaf stage for several reasons. At this stage, the seedling root system is sufficiently developed so that the seedling can become established after transplanting. The seedling root system is still small enough that root damage will not likely be extensive enough to kill or severely damage the seedling when it is lifted out of the flat or plug tray. The seedlings will not have begun to stretch or experience nutrient deficiency. Avoid any delay in transplanting. Although planting the largest seedlings possible might appear advantageous in terms of getting the crop off to a quick start, larger seedlings are also more prone to transplanting shock. In general, relatively young transplants provided with adequate growing space in the greenhouse produce the best stand and fastest crop development. The added stress associated with transplanting larger-than-optimal plants appears to substantially delay crop development. Cell trays require a slightly root-bound condition if plants are to be removed without damaging soil-to-root contact. Root-bound transplants generally reestablish more slowly than younger transplants.
Transplanting from Flats
As you prepare, make holes for the transplants in the medium filling the new container. Gently loosen the germination medium near the roots of the seedling being transplanted. Handle seedlings by the leaves only—even slight pressure on the stem can injure or kill a seedling. Lift the seedling from the germination medium where it has started to grow; allow any medium that is attached to the roots to remain. Do not bury the seedling deeper or raise it higher. Gently firm the medium around the root system, water thoroughly and place it in a good growing environment for that particular species.
Transplanting from Plug Trays
Transplanting seedlings from plug trays to finishing containers is fast and easy. Very little, if any, transplant shock occurs, and the seedling establishes itself rapidly. This plug transplanting process is often mechanized on an assembly line format with workers spaced along a conveyor belt that moves flats, pots, or other finishing containers.
Transplanting Machines
A wide-range of machines are used for transplanting plugs from those that are computer operated to less expensive versions suited for smaller greenhouse operations (See Figure 24.12). These machines are capable of producing several hundred transplanted flats per hour with minimal labor. A very desirable feature of most transplanters is that they are capable of transplanting from more than one plug tray size (e.g. 273's, 512's, etc.) into more than one flat insert size (e.g. 1203's, 1204's etc.).
Benefits of Transplanters
Transplanters can do a better, more consistent job transplanting than most workers. Because of that, the crop finish time can, in some cases, be shortened by five to seven days. Another savings that's difficult to calculate is the ability to continue to transplant and back-fill a second or third crop while most of the work force is involved in other activities. Transplanters have helped many growers stay on schedule. Many growers have noted that the transplanter sets a steady pace for their crew. It keeps everybody moving who is involved in the transplanting process because the machine is going to keep cranking the product out. At the same time, it makes their jobs easier (given an ergonomically efficient system setup with the transplanter).
Types of Transplanters
There are two major designs for transplanters. There is the “finger/pusher pin” design and the “needle” design. The finger-type design uses fingers and a planting foot that allows the gripper to make a side shift movement to get under foliage and a pusher pin that is synchronized with the extraction of the plug to insure all types of plugs are extracted, regardless of condition—underdeveloped with no root structure or over-developed with lots of foliage and roots that tend to adhere to the side walls of the plug tray. The finger-type design allows the operator the advantage of changing out the size of the gripper to fit the size of the plug.
Watering Station
Once the seedlings are transplanted, they are usually settled in with water. This gives the root system of the new plants good contact with the growing media and helps to give them a quick start. For small numbers of plants this can be done by hose and water breaker. When a transplanting table or automatic transplanter is being used, it saves labor to use a watering tunnel or water bar (See Figure 24.13). Besides saving considerable time, a watering tunnel can do a more uniform job of wetting the container after the plants have been transplanted. Watering tunnels are designed to irrigate flats or pots held in a carrier or hanging basket
Transplant Containers
A wide variety of containers are available for transplanting seedlings. Containers should be economical, durable, and space efficient. After a container is selected, it can be expensive and time consuming to change to another type. Most greenhouse operations grow a wide variety of species and therefore several different containers are required. Container choice for a particular plant species depends on root system morphology, target plant criteria, and the growing conditions. Often, seedlings are started in smaller containers and then later moved to progressively larger containers.
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