Choosing Containers for Plants
Choosing a container for any kind of landscape plant outdoors is not all that complicated. There are only six questions to answer and you will know exactly what kind of container you are looking for at the garden center. For each question, we go into more detail on the left.
Size - How big is the plant, or more important, how big will that little seedling become when it is mature?
Think “small”, “medium” or “large” container. You may need to start “small” and then repot to a larger container over time. Size includes the width as well as the depth of pot. In most cases you want a container that is about as deep as it is wide and about ½ again larger than the size of the root ball of the plant or group of plants.
When in doubt about the size of container, one secret to success is–go big. Plant in a large container and you’re assured the pot you have chosen has enough space to support your plants as they grow throughout the season. And bigger pots hold more water and need watering less often.
Assuming we are talking about containers for plants outside in the yard, a one gallon container is about the smallest practical size you can use outdoors especially if you plan to use a number of plants in the container. A one gallon container is about 8 inches wide and 12 inches deep. In smaller containers outdoors, plants tend to dry out too fast.
If you are repotting a plant or group of plants that have gotten root bound, the new pot should be at least 2 to 4 inches larger in diameter. That's enough space for new root growth without making the pot a great deal heavier. In general, it's best to move up gradually in pot size.
Drainage - Think about drainage
While there exceptions, if you are a beginning container gardener, you should always start with containers that have drain holes in the bottom or side of the container – no exceptions for the beginning yardener. Drill holes if necessary.
We believe that all containers outside should have drainage holes on the bottom or on the lower side. Most manufactured containers have drainage holes, but some do not. If you have a container without drainage holes, you can make the holes with an electric drill. The hole should be at least one quarter of an inch in diameter to avoid its getting clogged. Depending upon the kind of pot, a masonry bit may be required.
Drip trays - Indoors, drip trays are important to avoid getting water on the floor. However, outside on porches or patios drip trays can also be important for baskets, window boxes, containers suspended over doorways, or containers placed wherever stains from escaping water might be a problem. A drip tray can be a simple terra cotta saucer under a terra cotta pot or a clear plastic tray.
Cache Pot Technique - If you have a large ceramic container which does not lend itself to having holes drilled in the bottom, you can use “cache pot’ technique used with indoor houseplants that need high levels of humidity. You simply set one container with drainage holes inside a non-draining container.Put a layer of gravel in the bottom of the outer container, and set the container with holes inside on top of the gravel.
Material - What material is the container made of?
For most beginning yardener container gardeners a plastic container will do the job while at the same time being the least expensive and the lightest of all the other materials such as terra cotta, clay, or wood.
Consider whether you may want to move the container to a different location from time to time. If so, keep in mind the weight factor after the container is full. Styrofoam peanuts can be used in the bottom of a large container rather than filling it fully with soil mix.
While plastic is probably the most common material used for making containers there are many other materials that you may wish to consider for certain situations or looks.
Plastic containers - The main reason that plastic is so popular is that they are among the least expensive. Because they are lightweight, they are good for balconies and flat roofs, and generally are easy to clean. They are easier to move around. Plastic can be manufactured in bold contemporary shapes. Because plastic is impervious to moisture, water does not evaporate as it does in terra cotta, and plant roots tend to be slightly warmer in plastic.
Terra cotta containers- Many gardening books give the impression that the best material for a container is terra cotta, that orange red clay material. It’s true that plants will generally be happier in a terra cotta pot compared to a plastic pot because the sides of the material, being clay, is porous and therefore actually allows air into the root zone from the sides as well as from the surface of the soil; more air available means happier plants. The down side of this benefit is that all unglazed terra cotta containers need to be watered much more frequently than do plastic containers. On the other hand, they are relatively inexpensive and because they absorb excess water, they reduce the chance of damage to plants from overwatering. Then back to the down side, the exterior of a terra cotta container is somewhat rough and tends to become stained from fertilizer or algal growth. Some consider this attractive, but it makes pots more difficult to clean and disinfect. Terra cotta can chip and crack in severe cold, and it requires careful handling any time of the year.
Glazed terra cotta—or any ceramic—has a glossy finish that slows moisture loss and evaporation. Glazed pots are easier to clean but more expensive than the porous ones.
Wooden containers – Wood is a good insulator, moderating temperature extremes. Wooden containers include things like used half whisky barrels, window or deck boxes, or just round containers made of wood. Cedar, redwood, and cypress are the best woods for containers, since they are naturally resistant to rot and most resistant to weathering. All wooden containers must have sufficient drainage holes to insure that water does not sit inside the container for very long.
Any wooden container sitting on the ground is going to rot in the bottom pretty quickly. Keep wooden containers up on bricks or wooden blocks so there is no direct contact between the bottom and the soil. Wood rot accelerates in rain and snow, so if you plan to leave your wooden containers outdoors in severe weather, concrete and stone may be a better choice.
Concrete containers - Concrete can be molded into different shapes with different textures. It can be used to make reconstituted stone at less cost than authentic stone. Concrete has good insulating properties, buffering plants and soil from sudden extreme temperature changes. Weight, however, is a limitation with concrete. Concrete should always be fully cured and weathered so it doesn't affect potting soil alkalinity.
Fiberglass containers - Fiberglass makes an excellent though sometimes expensive outdoor planter. Because fiberglass is frost-proof, lightweight, and durable, it works especially well in roof gardens where weight is a consideration.
Color - What color do you want?
Watering - Which watering technique do you prefer to use?
Do you want a regular pot or one that is designed to store water in a reservoir and water the plant over a longer period than a regular pot will. These are called “self-watering”, “continuous watering” or “controlled watering” containers. Their big value to a yardener is that they help avoid a major disaster is you forget to water the plant.
There are a number of designs for what are called “self-watering” containers. In all cases, there will be a space at the bottom for a reservoir that will store a modest amount of water. Most reservoirs have a hole in the side of the container that provides an overflow escape if too much water is put into the container. The top part of the reservoir will have some means for the potting soil to be in contact with the stored water and therefore, by ______, be able to take up the water as the plant uses up that water already in the potting mix. There are usually some holes in the roof of the container that will also allow roots to penetrate down into the water as the plant matures.
Most plants will do fine in self-watering containers, however there are some that really don’t like to have such a steady level of moisture. They want the moisture level to go dry then wet then dry again which is basically the situation found outside in nature.
Some self-watering containers are easier to fill than others. Otherwise, most of them work very well and help the yardener avoid letting the plant go to the wilt stage for lack of water.
Design - What design are you looking for?