Nursery beds are garden beds devoted entirely to starting plants, both from seed and by vegetative propagation. They may be in the garden itself or elsewhere, but wherever they are located, nursery beds are planned and planted as the temporary location of the plants, not their final growing site (Figure 8.1).
One indigenous example comes from central Mexico where a system of canal-fed gardens is used and special nursery beds are constructed for starting grain amaranth seedlings during the dry season. A rectangular bed measuring approximately 2 m × 15 m (6.5 ft × 50 ft) and 4-5 cm (1.5-2 in) deep is filled with rich, muddy soil scooped up from the canal bottom. The next day as the soil dries it is cut into 3 cm × 3 cm (1.25 × 1.25 in) squares with a special slicing rake called a cuchilla. Using a small stick or their fingers, the gardeners make a small hole 1 cm (less than 0.5 in) deep in the middle of each square and then drop amaranth seeds in. The bed is sprinkled with manure which is then swept off so only that which falls into the planting hole remains, covering the seeds. Twenty to 30 days later the seedlings in their soil cubes are transplanted into the garden beds. Where clayey soil is available gardeners can try making soil cubes to start transplants (section 8.2.2).
Nursery beds allow the gardener to concentrate and save resources such as water and time, and to take advantage of favorable microclimates for early or late-season germination. For example, in temperate drylands warm-weather plants can be started in sunny, protected areas before the end of the cool season. Moving nursery beds seasonally or yearly helps avoid problems with nematodes which can build up in continuously cultivated soil (section 13.3.2).
Containers offer many of the benefits of nursery beds with the added advantage of being easily moved to adjust to changes in sunlight, shade, temperature, and the gardener’s schedule. Containers are often used for starting cuttings or seedlings for transplanting. Some plants, whose leaves or small fruit are continually harvested in small quantities for seasoning or medicinal purposes, are kept permanently in containers. Examples include mint, basil, oregano, marjoram, rosemary, epazote, and chili peppers.
Containers may be the only option for urban gardeners with little space and no access to land. For them, permanent container plantings on rooftops, in windows, or on balconies can provide herbs, condiments and some greens for the household meals (Figure 8.2).
A wide variety of locally available and free or inexpensive containers can be used for planting including calabashes, pots and pans with holes in the bottom, baskets, steel cans, wooden boxes, trays, cardboard cartons, plastic bottles, and other made, found, or discarded materials (Figure 8.3). Galvanized steel containers are not good because this material gives off zinc salts toxic to plants.
Baskets made of leaves or other plant fibers make excellent containers for eventual transplants. Often there is no need to remove tree seedlings from a basket container when transplanting, because the basket will eventually decompose in the soil, thus avoiding disruption of the tree’s root system. However, the basket fibers should be cut through and pulled open in several places before planting the tree. This is especially true if the basket is tightly woven or made of a tough, woody material. Planting containers should not have been used for paint, fuel, pesticides, or other substances that can harm the seedling, contaminate the garden where it is transplanted, or poison people and animals.
Containers can be of any size and may hold one or more plants, but should be small enough so that the gardener can move them without difficulty. However, very small containers, such as a cup, are not appropriate for most plantings as they offer little room for the plants to grow and insufficient soil from which to receive nourishment. Also, the larger the container the more soil there is for holding water, and the less frequent the waterings need be. Containers should be deep enough to allow the seedling’s roots to develop to the stage when they can withstand being transplanted. To allow transplanting, the top opening must be as big, but preferably bigger, than the bottom, making it easy to remove seedlings without damaging their roots (Figure 8.4). Vertical ridges on the inner surfaces of containers prevent roots from growing in a spiral pattern which results in root-bound seedlings (section 8.4.4). A community garden or tree nursery project that includes local manufacture of containers can design them with a cone shape and vertical ridges on the inner surface (Figure 8.5)
The relatively small amount of soil in containers can dry out rapidly and the soil temperature can rise and fall to extremes of hot and cold, all of which are harmful to plant growth. Containers with thick walls provide better insulation, reducing temperature fluctuations. Under sunny, hot conditions light-colored containers are good because they reflect sunlight, and thus heat, away from the soil. In the cold season or in cold areas, dark-colored containers that absorb sunlight and heat may be better. A container can be shaded and insulated by wrapping it with cloth, or by mounding soil, compost, or leaves around it.
Containers must allow drainage of excess water or else waterlogging (section 12.6.1) and damping-off (section 13.4) will occur. Holes can be made in containers of most materials except glass and fired clay, which are so brittle that holes cannot be made in them without breaking. In addition to holes, a few small stones or pieces of broken clay pots in the bottom of containers can improve drainage.
Salts in water or soil can accumulate on unglazed ceramic containers, appearing as a white patina or coloring on the outside surface. If this occurs, the empty container can be submerged in water for several days and scrubbed to remove the salts. Using rainwater will reduce salt buildup in locations where this is a problem with other water sources.
Soil cubes are good for starting transplants because the seedling’s roots are not disturbed by removing the soil from a container. The soil cubes described in section 8.2.1 are slices of a special type of nursery bed, but soil cubes or blocks can also be made and used like containers. One way to make the blocks is to press the wet soil into a form such as a container or even a hole in the ground. Then as it dries, it is sliced into squares which will be cubes when removed from the form. However, as already mentioned, the soil used must have the right clay and humus content to hold together in blocks until it is time to transplant. Timing of transplanting is also important, because if the seedlings’ roots grow out of the soil block they have no protection and will dry up or be injured when transplanted.
Filling the container about three-quarters full leaves room for adding enough water to soak down to the plant’s root zone (Figure 8.6). In Chapter 9 soil qualities good for the garden are discussed. The same qualities are good for container soil mixtures but with an even greater emphasis on good drainage. The planting mixture must be able to hold some moisture but both soil and container must allow good drainage because water saturated soil encourages disease problems. How the mixture is made depends on the local soil.
If soil-borne diseases are a problem, heating small amounts of soil, called soil sterilization, can help. Heating moistened soil to 71°C (160°F) for about 30 minutes kills most bacteria and viruses. In areas with high daytime temperatures, moist soil could be put in a covered metal pot or closed plastic bag and left to heat up in the sun for several days. Because heating the soil also kills beneficial microorganisms it should only be used when absolutely necessary.
Before planting, the soil in the container should be leveled and wet throughout. After this, drainage can be tested by adding water up to the container’s rim. If there is still water standing on the soil surface after about 15 minutes, the drainage needs to be improved. The drainage openings in the container may need to be enlarged or more organic matter or sand added to the soil.
In large containers the gardener can make planting depressions for seeds using her fingers or a stick. Small containers concentrate water on seeds so there is no need for planting depressions. In small containers seeds can simply be sprinkled across the soil surface (Figure 8.7), covered with a layer of dry garden soil (section 6.4.5), pressed down firmly, and the planting area gently watered.
Containers should be kept in a convenient location with adequate shade and sunlight. Sometimes the drainage holes become clogged by the surface on which the container is resting. If this happens putting gravel under the container can help by making air spaces that water can pass through to drain out of the wet soil in the container. The soil surface should be allowed to dry slightly between waterings (section 6.5.1).
Sometimes planting seeds directly in the garden is more appropriate than container or nursery bed planting. The primary advantage of planting directly in the garden is that the plants will not be moved, and therefore their growth will not be disturbed by hardening-off (section 8.4.4) or transplanting shock. For example, seedlings of cucurbits and some root crops may die or their growth may be severely slowed by transplanting. Direct planting also eliminates work for the gardener. The gardener’s schedule or the garden location may make it convenient to care for the seedlings right in the garden with less work, and the garden environment may be good for starting seedlings.
These advantages must be weighed against the possible disadvantage of direct planting: increased vulnerability to pests and the elements because management and resources are not as concentrated as with nursery beds or containers.