Greenhouse Plant Containers
Container Types
Many types of containers are available, and each has its advantages and disadvantages. Despite the large variety of products available to the grower, “growing success” often is contingent upon growing techniques rather than the choice of container and medium. Several container types are used in greenhouses and can vary considerably in size (Table 14.1).
One-Time-Use Containers
One-time-use containers are of various sizes, round or square, and are made of fiber, such as coir or compressed paper. Some include a natural or synthetic binding material such as resins, glue, wax, latex, and even cow manure. Dry, they will keep indefinitely. Since these pots are biodegradable, they are set in the soil along with the plants. Peat pots find their best use where plants are to be held for a relatively short time and then put in a larger container or in the field. Fiber containers are semi-porous and promote water and air exchange between the rooting substrate and surroundings. Other containers rely on the material itself to provide structural stability and extended life span for long-term use.
Jiffy 7® Peat Pellets
The Jiffy 7 peat pellet is made completely of peat, with fertilizer added, enclosed in a plastic net, and compressed for easier handling, shipping, and storage (Figure 14.1).
Jiffy® Super Pellets
Jiffy super pellets consist of dry, compressed peat growing media inside a soft-walled, meshed bag and come in a variety of sizes.
Jiffy® Pots
Jiffy peat pots are square or round pots made out of compressed peat (Figure 14.3). They are typically 2 to 3 inches (5–7.6cm) across at the top. The pot, when filled with a root medium, is ready to use for rooting cuttings or germinating seeds.
Rockwool Cubes, Blocks, and Slabs
Rockwool, a lightweight hydroponic substrate, is made from spinning molten basaltic rock into fine fibers, which are then formed into a range of cubes, blocks, growing slabs, and granular products. Because rockwool and other stone or mineral wools used in horticulture originate from rock, they are considered by many to be a natural product. Rockwool is a widely utilized substrate in commercial horticulture for the production of crops as diverse as tomatoes, melons, cucumbers, peppers, strawberries, herbs, and cut flowers; however, it can also easily be used by smaller hydroponic growers wanting to take advantage of improved root zone technology.
Zipset™ Propagation Trays
Zipset Plant Bands are square growing containers made from milk carton paperboard (Figure 14.7). The paper provides exceptional strength when wet yet is still 96 percent biodegradable.
Paper Pots
Paper pots or paper tube pots are more popular with seed plug and cutting propagation of ornamental, vegetable, and forestry species (Figure 14.8). They allow for greater mechanization with pot-filling machines, automatic seeders, and wire benches that allow air pruning of the root system. Typically, paper pots consist of a series of interconnected paper cells arranged in a honeycomb pattern that can be separated before out planting.
Single, Free-Standing Containers
Several types of single-cell containers are being used to grow native plants for specific conditions.
Treepots™
Treepots are excellent for budding, grafting, and starting larger seedlings. These unique, deep, narrow containers are constructed of flexible hard plastic and are available in many different sizes (Figure 14.9).
RootMaker® Containers
RootMaker containers have staggered walls and a staggered bottom that prevent root circling and direct roots toward the holes in the walls and the bottom of the container. Each step complements the next, building upon the previous fibrous root system.
Polybags
Poly bags made of black polyethylene (poly) plastic sheeting are the most commonly used greenhouse containers because they are inexpensive and easy to ship and store (Figure 14.11). They are considerably less expensive than rigid plastic containers and seem to be satisfactory, but some types deteriorate rapidly. They are usually black, but some are black on the inside and light-colored on the outside.
Hanging Baskets
Hanging baskets are also made from plastic but of a heavier grade than that used for flats (Figure 14.12). Hanging baskets come in a variety of colors and styles. The most commonly used sizes are 8- and 10-inch (8–25cm) diameters, with and without saucers on the bottom to collect runoff water.
Clay Pots
Root media in clay pots are well aerated and are less likely to develop root rot diseases (Figure 14.13). Clay pots often last a long time and can be used and reused many times, provided they have been steam-sterilized. However, the use of clay pots has declined over the years due to a number of factors.
Plastic Pots
Plastic pots are available in many sizes, shapes, and colors. Plastic pots are lightweight, a characteristic that means lower production costs and easier handling of crops. Some types are fragile, however, and require careful handling, although other types, made from polyethylene, are flexible and quite sturdy. Since plastic pots are not porous, fertilizer salts cannot pass through the walls of the pot as in the case with clay pots. Any residues that do accumulate on the plastic pot are easily removed. Also, the roots in plastic pots require less frequent watering since air cannot pass through the walls of the pot.
Exchangeable Cells Held in a Tray or Rack Containers
The major advantage of growing plants in individual cell containers supported in a hard plastic rack or tray is that the individual cells are interchangeable, allowing for consolidation and spacing as described earlier. Racks are designed to create enough air space underneath to promote good air pruning. Plastic cells can be reused for several growing seasons.
Ray Leach Cone-tainer™ Cells
One of the oldest container designs on the market, the Ray Leach Cone-tainer cells are still popular with native plant growers (Figure 14.14). In this system, individual soft, flexible plastic cells are supported in a durable hard plastic tray. Trays are partially vented to encourage air circulation between cells and have a life expectancy of 8 to 10 years.
Deepots™
Deepots are single cells constructed of thick plastic and held in hard plastic racks (Figure 14.15). Available in several sizes, they have internal vertical ribs for root control, and supports on the bottom of each container provide stability.
Book or Sleeve Containers
Spencer-Lemaire Rootrainers™
These unique book containers are composed of flexible plastic cells that are hinged at the bottom, allowing the growing media and root system to be examined during the entire growing season when the books are open (Figure 14.16).
Rectangular Block Containers Made Up of Many Cavities or Cells
Styroblock™ and Copperblock™
Styroblock containers are the most popular type of container used in forest nurseries and are available in a wide range of cavity sizes and densities (Figure 14.17), although outside block dimensions are standard to conform to equipment handling. This container has also been used for growing native grasses, woody shrubs, and trees. The insulation value of Styrofoam protects tender roots from temperature extremes and the white color reflects sunlight, keeping the growing medium cool.
Propagation Containers
Plug Trays
Plug trays are very common containers in the greenhouse (Figure 14.18). Plug trays are useful for germinating seeds or rooting cuttings since they permit young plants to be moved easily. The size of plug trays that has been most commonly used in the industry for years is 11 inches wide by 22 inches long (28 x 56cm).
Cell Plug Try Inserts
Cell plug tray inserts are placed inside the trays, allowing the grower to easily separate species in one tray, reducing potential disease spread, and easing transplanting (Figure 14.19). When the bedding plants are ready for transplanting, the plants are easily pushed out of the cell pack and transplanted without any damage to the root system.
Flats
Currently, container flats are almost exclusively plastic (polyethylene or polystyrene), 11 by 22 inches by 2.5 inches deep, and are referred to as flats or as a 1020 flat (Figure 14.18). Flats are easily cleaned, reusable, and can be nested and stacked for space-efficient storage.
Click on the following topics for more information on containers for growing greenhouse crops.
