There is a unique appeal to container planting. Using pots, whiskey barrels, and old bathtubs has its aesthetic value. Containers often let us put plants in places we couldn’t otherwise and give more variation to elevations of plantings. But as fun and convenient as it might all sound, how can you figure out if it will really work for you? This list of things might help you decide how and where to use containers:
1. Watering — Containers require more regular evaluation for water needs. Not only do they have a more limited reservoir than an open plot, but the plant roots are more constrained and not able to send out the same network of roots. Containers, depending on what they are made of and where they are located, can be subject to getting drier more quickly than most open soil situations; or they stay wet longer. Death by drowning is fairly common for container plants in the shade. Even if they stay wet longer, there is often a shorter window of time available to adjust the water content to keep the plant healthy. Plus, plants tend to be stuffed more closely into pots. This all means more monitoring. Using timed watering is more challenging, as it is hard to set it at a level that meets needs as the seasons change. See other specifics under #7 when types of containers are discussed.
2. Climate and microclimate — Containers set out in the open in an arid climate, like southwestern Idaho, can get very hot and dry quickly, making it hard for all but the most drought resistant plants to survive. However, experimenting with microclimates around the yard can make it possible to grow things in unlikely spots. For instance, the roots of a large tree might make it difficult or impractical to plant directly into the ground there, but a container or two can make use of the shade. You can stick to splashes of color with bedding plants, or you could try to grow a flowering vine, like a heavenly blue morning glory, up into the tree, and fake having a flowering tree all summer, assuming the branches are strong enough to support a particular vine.
3. Fertilizing — Many potting soils come with an initial load of nutrients, but after that plants in containers need more supplementing than most plants that are directly in the ground. The normal organic processes that take place in the open ground seem to be limited in containers. Not all of the same creatures can get in there; and the un-dirt-like qualities that make the standard potting soil a bit nicer for containers, make it less likely to support a natural organic system and compost.
4. Portability — Containers are nice for tender plants that you want to over-winter, assuming you can find winter quarters with an appropriate environment. Some plants will want to be dormant over the winter, but some will want to to keep on growing. The thing to keep in mind is that a container full of even slightly damp soil can be pretty heavy. The width and height of the plant also need to be considered. Unless you have a location to dedicate to this every winter, options are limited. Another advantage of the portable, restricted nature of containers is that it can provide a way for putting plants up closer to the house without the same risks of water damage there are from watering directly in the ground.
5. Plant Size and Shape — This is obviously limited to some extent by container size, but partly depends on how much you want to attend to the plants. Larger plants can thrive reasonably with more attention. Pruning can help manage some plants that might otherwise overrun their acceptable boundaries. Supporting structures can be used to increase upward growing space.
6. Pests — Cats seem to be particularly attracted to potting soil as a litter box option, and even as a warming spot. Once the plants are filling in the pot, this is not usually as much of a problem, but when they are smaller, a few well placed plastic forks help a lot. It might also be possible to put up a temporary wire cage over the container, especially if it is larger. The container plants will not be as likely to have problems with ground traveling pest, like moles or cutworms, but if there is any watering stress, damage from flying or crawling insects can be more devestating.
7. Types of Containers — Any container that can be arranged to drain well is a possible planting container. Holes can be drilled in old metal bins or plastic buckets. You can form your own containers using ideas from books like Making Concrete Garden Ornaments. It all depends on the look you are going for and what your needs are for moderating temperature, as well as everything mentioned about portability and plant size. The material that the container is made of will affect how much water is lost through the sides. Unglazed terra cotta pots get dried much faster than most other pots. Plastic pots retain water a long time, even if there is drainage. Don’t assume that a material you think of as porous is draining, even if other container of exactly the same type have done fine. Once I had two whiskey barrels within five feet of each other in the same light and water conditions, but one of them was turning into a bog! Drilling a few holes around the outside perimeter of the bottom of the offending barrel took care of that. Some types of material are obviously heavier than others, but after a point it is the volume of potting soil that matters most and any container will be heavy.
Containers can be the best option in some situations, but make gardening more trouble in others. A little forethought should make it more of the best with minimal trouble.