Container gardening – A summary

As I am currently studying possibilities to grow vegetables in plastic bottles and plastic bags, dwelling around all over the surface of the Earth, I felt the need of summarizing some data on container gardening.

The title of this message says clearly what it is : A SUMMARY, not more, not less. But maybe it will be useful for some “starters” in container gardening. Instead of searching the Internet, they will find a number of general guidelines, which may be useful before getting their hands dirty.

2007-02 – First steps in a small study on growing vegetables in plastic bottles : a lettuce seedling in a decapitated coca-cola bottle with a perforated bottom, and a cauliflower plant in a mineral water bottle. These plants grow well !

2007-02 – Les premiers pas dans une petite étude de la culture de légumes dans des bouteilles en plastique : une petite laitue dans une bouteille de coca-cola décapitée avec le fond de bouteille perforé, et une plante de chou-fleur dans une bouteille d’eau minérale. Ces plantes poussent bien !

CONTAINER GARDENING

Unlimited possibilities

Your ability to garden may be limited by many different factors. Then consider container gardening. The simple concept of growing plants in pots or even in plastic bottles, offers you a variety of ways to enjoy gardening. All you are looking for is: some containers, the right growing medium, a nice choice of plants (seeds, seedlings or young plants) and a window, balcony or porch and you’re on your way to become a “container gardener”.

Containers will offer you the joy of growing plants in an area where traditional gardening is impossible. Even with limited space, you can grow plants anywhere: on a window sill, a doorstep, a balcony, a stair, and a patio, even a rooftop, in hanging baskets or in old buckets. They all can provide enough space for an attractive and even productive (e.g. for vegetables) display. You can also grow different plant species in one single container in ecological relationships. Container gardening makes observation easy and, whenever necessary, containers can easily be moved around.

A well-planned container garden can be attractive (ornamentals) as well as useful (vegetables, fruits, herbs). Taking good care of it will result in a beautiful, and functional display, but whenever deciding to give it a try: start small. Smaller gardens result in lower costs. Initial costs for container gardening may be a bit higher, but once all the necessary materials are purchased, costs are extremely limited: less growing medium, less fertilizer, fewer plants.

Container gardening is only limited by lack of imagination.

Who is who in container gardening?

Many people are directly interested in container gardening:

• People without garden space or with bad soil in their garden.
• Urban people living in apartments or studios.
• People with limited time for gardening.
• Elderly or disabled people with limited mobility.
• Flowers or herb lovers.

Choice of containers

Almost any type of container can be used for growing plants: planter boxes, bushel baskets, drums, gallon cans, tubs or an old discarded wheelbarrow with soil and drain holes in the bottom. Containers can be purchased, built or recycled from all kinds of materials. It is always important to choose containers that best accommodate the chosen plant species. Containers come in a variety of sizes, shapes and materials. The choice will depend upon the type of plant and the location. The size of the container will vary according to the crop selection and space available. Keep in mind that the size, material and shape of the container should be conducive to your plant’s health.

Consider the following guidelines when choosing your container:

• Generally, avoid containers with narrow openings.
• Plastic containers are lighter weight, but can become brittle in cold temperatures or may deteriorate in UV of the sunlight. They are not porous and keep water over a longer period.
• Terracotta containers are porous, but are heavy, break easily and tend to dry out more rapidly.
• Glazed ceramic pots require several drainage holes.
• Wooden containers can be built to sizes and shapes that suit the location. Many are susceptible to rot. Redwood and cedar are relatively rot resistant.
• Hanging baskets, often made of wood or wire, can drizzle onto furniture or the floor.
• Metal containers heat up rapidly which can cause root damage. Using a clay or plastic pot as a liner can help.
• Wrought-iron stands can minimize wood rot.
• Window boxes are usually made of wood or plastic.
• Stone containers create a natural effect, are often difficult to move and break easily.
• Sunken containers work well for plants that spread easily. One can either bury the whole container or embed the rim to restrain the plant.

Use containers with sufficient capacity, according to the size and number of plants to be grown in them. Small pots restrict the root area and dry out very quickly. Deep-rooted vegetables require deeper containers.

Generally, most plants can be grown in containers as long as ample space to develop roots is provided. Shallow-rooted crops need a container at least 15 cm (6 inches) in diameter with a 20 cm (8-inch) soil depth.

Containers should have adequate drainage holes on the bottom or sides near the bottom to prevent waterlogged soil and rotting roots. Line their base with a layer of coarse gravel, a piece of newspaper, a sheet of plastic etc. to prevent soil loss through the drainage hole.

In hot climates, use light-colored containers to lessen heat absorption and discourage uneven root growth. Dark colored containers absorb more heat, which can damage plant roots and make it difficult for them to thrive.

Place containers on brick feet or blocks to allow free drainage or place a saucer under them to catch excess drainage.

Line hanging baskets with sphagnum moss for water retention. Keep baskets away from afternoon sun. When filled with moist soil, weight of the container can be a negative factor. When installing a large container, mount it on castors so that it can be moved easily.

Match the plant to the pot. Consider how large the plant is likely to get at maturity, and pick a pot that gives it plenty of room to grow.

Likewise, consider the shape of the container because some pots can pose problems. A round pot is fine for growing all kinds of plants, but at the end of the growing season when it’s time to remove the plant from the pot, that task is often easier said than done. When the plant’s roots grow into the wider portion of the pot, it’s difficult to get the plant out of the pot without severing the roots,

Saucers for containers

For all types of containers one needs a saucer to capture the loose soil and dripping water that escapes from the bottom.

Most plants prefer to be watered from the top down rather than wick the water up from below. When excess water drains out of the container, spaces open up in the potting soil and air fills those spaces. It activates the microbiological activities in the soil, which helps to make nutrients available to plant roots.

When the surface of the container dries, the surface of the potting soil tries to pull moisture up from the bottom of the pot, but rarely does it make it all the way up. So if only watering from the bottom, using a saucer full of water, it will never flush the soil, which can lead to accumulation of salt deposits on the container wall.

Growing media

A lightweight, well-draining, porous growing medium is needed, but it should also retain sufficient moisture because roots require both air and water. It should contain a lot of organic matter (microbiological activity).

Outside garden soil should preferably not be used, because it is mostly too heavy (clayey), compacting when drying and then pulling away from the container wall.

Commercial potting mixes are relatively lightweight, but often slightly acidic; adding some lime may help to grow certain plant species (soil test: pH around 6.5-7.0).

You can also mix your own: one part loamy garden soil, one part peat moss, one part coarse (sharp) sand, and a slow-release fertilizer (14-14-14) in the right dosage per volume. Some gardeners do not recommend peat moss (environmental concern), but compost.

Synthetic “soil” suits very well for vegetable container gardening. This mix may contain a number of different materials: peat moss, sawdust, wood chips, coir (coconut fibers), bark products, perlite, vermiculite, …

According to many gardeners a “soilless” potting mix (from a garden center) works best for container gardening. They drain quickly, are lightweight, designed specifically to deter insects and soil-borne diseases and are free from weed seeds.

Filling the container

When filling a container, leave at least a 5 cm (2 inch) space between the top of the soil and the top of the container for adding some mulch (about four-fifths full). Make it 10 cm (4 inches) for plants that need a lot of watering. When watering the container, the growing medium (substrate) will settle.

Seeding and transplanting

Seeds can be germinated in any container filled with a good substrate. Cover most seeds to a depth of 0.5–1.5 cm (1/4 inch to 1/2 inch) for good germination. Seedling production should be started in a warm room with sufficient sunlight. It takes 4 to 8 weeks before transplantation date into the final container.

Easily transplantable vegetables are very suitable for container gardening. Seedlings are available in local garden centers or nurseries, or they can be grown at home. Most vegetable seedlings should be transplanted after developing their first two to three leaves. Transplanting must be carried out carefully to avoid injuring the young roots.

Planting in containers

Plant at the same time as in a regular garden. After planting, water the soil gently. Should stakes or other supports be needed, provide them when the plants are very small to avoid later root damage.

Sunlight

Where to put a container, is governed by the growing requirements of the plants it contains. Most vegetables grow better in full sunlight than in shade. Plants that normally grow in full sun may well benefit from a bit of afternoon shade, especially in places where they can heat up very quickly. However, it is possible to position each of the containers in places where they have the best possible growing conditions. It is also better to foresee a source of water close to the containers for easy watering.

The amount of light the container plants will need varies with the plant species. It will determine which crops can be grown. Leafy vegetables (lettuce, parsley, spinach, cabbage,) tolerate shady places, while root crops (radish, turnip, beetroot,) and fruiting vegetables (tomato, peppers, cucumber, eggplant,) need more sun. Most plants require a minimum of 5-6 hours of direct sunlight per day. Some gardeners use reflective materials, like aluminum foil or white-painted surfaces (even glass or marble chips) around containers to increase somewhat the available light.

Fertilizing the containers

Since potting mix drains water rapidly, nutrients will be washed out of the container (leaching) with frequent watering. Therefore, it is necessary to supplement growth of container plants with fertilizer.

After the first month of growth, add a diluted organic fertilizer (manure tea or compost tea, seaweed extract) when watering. One can apply such a diluted fertilizer every two weeks and adjust fertilizer levels as necessary, but remember to provide the plants with a variety of nutrients (mineral and organic, also trace elements). Follow the recommended rate of any fertilizer to avoid fertilizer burn by lack of soil volume

It is advisable to leach all the unused fertilizer out of the soil mix by thoroughly watering all containers with tap water to prevent buildup of injurious materials in the soil mix.

Watering

Because the volume of soil is relatively small, proper watering (generally once a day) is essential for successful container gardening. In an exposed location, container plants loose moisture very quickly by heating or wind. Small pots, clay pots and other porous containers have to be watered more frequently. So do larger plants. Not all plants need to be watered at the same frequency. Some prefer even drier conditions, like succulents and cacti, which may go several days or even weeks without watering. Water should reach air temperature before applying it to temperature sensitive plants.

If the potting mix is getting dry every day (Check the soil mix daily in warm temperatures; it should be moist 2-3 cm or 1 inch deep), group the containers together so that all leaves create a sort of canopy shading the soil and keeping it cooler. Mulching the containers with grass or gravel pebbles and installing windbreaks helps to reduce moisture loss by evaporation.

If possible, water late in the day to reduce the hydric stress on the plants. Soak the potting soil very well and water again a bit later. The first watering usually leaves dry cavities within the potting mix, while the second watering fills them.

Wetting the leaves should be avoided since that can cause leaf diseases.

Plant species for container gardening

Varieties of different species have been developed specifically for container use (growing fresh, nutritious vegetables is possible on a window sill, a doorstep or a balcony). Most of the container plants are chosen because they are esthetically nice, but not necessarily edible.

Some fruits, vegetables and herbs provide a remarkable aroma and taste. Consider planting parsley and carrots together, since parsley repels carrot flies. Those who can grow rather well in containers are unlimited and they can grow well together. However, it is better to start with only a few favorite things. Generally, small crops, which have a quick maturing period, are ideal, and compact varieties of normally large plants perform better, but vertical “climbers” also adapt quite well to container conditions, but they require more space because of their vining growth. Quick-growing small herbs and leaf lettuces can be planted around larger fruiting vegetables. Many herbs can be grown easily from seed. Since their seedlings mostly need dark, warm and moist conditions, they thrive well in small container. They can later be transplanted or moved to the outdoor garden. When needed, container plants can be sheltered during periods of high temperatures.

Consider growing mint, since it grows quite easily in larger containers (30 cm or 1 foot). Unlike parsley, mint cannot be propagated from seed, but from cuttings. Once it mint grows, it can be harvested at any time, and cuttings can be taken for multiplication.

Many successful container flowers (annuals and perennials) are grown in containers. Annuals are very easy. Perennials can grow larger over time and a combination with the right annuals might look overwhelming. Bulbs behave like annuals. It is easy to save them year after year and to collect bulbils for propagation.

One can also grow shrubs and trees. Some will flower, others not. Fruit plants need more attention. They need to be pruned and fertilized regularly. Permanent spots for larger plants may be necessary. However, some fruiting plants like figs can be kept in container with constant pruning.

There will always be a need to build up the soil every year.

Diseases and Insects
Plants grown in containers can be attacked by various types of insects and infected with diseases that are common to any other type of garden. Plants should be periodically inspected for the presence of foliage and fruit-feeding insects, as well as for the occurrence of diseases.

Containers can be arranged so that plants can attract and repel insects or flies. Some plants emit special chemicals (allelochemicals) from their roots or leaves, which repel pests. See books or Internet information for specific examples.