Cooperative Extension Fact Sheet FS1215 | October 2013
Any site with ample light and accessibility for watering is perfect for container gardening with flowers and foliage plants. Many plants that can be grown in a garden can be grown in a container. Container gardening is ideal for anyone with limited gardening space or an inability to tend to a traditional garden. Container gardening allows for creativity in a small area. It can bring a garden of any size to the doorway, balcony, terrace, rooftop, windowsill, or practically any outdoor location.
When creating a mixed flower and foliage planter, the key is to select plants that will all thrive with similar sun, temperature, and nutrient requirements. Choose your location, and then match the plants to it. Be adventurous. Experiment with different combinations. It is possible to mix annuals, perennials, vegetables, houseplants, herbs and grasses into your creation, as long as their cultural requirements are similar. Avoid choosing slow growing and vigorous plants for the same container, as one will overpower the other by the end of the growing season. If possible, select plants that are easy to care for and will perform well over a long period.
Scale is a very important factor to consider when designing. A tall plant will need a container with a wide base for stability, while a cascading plant will need a pot high enough for it to drape over the sides.
A long horizontal planter, such as a window box, becomes united by the use of repetition. For instance, all pink begonias with cascading ivy or trailing Torenia, regularly spaced, would create a very pleasing effect. Also, selecting foliage and flowers of varying shapes, sizes and textures adds greater interest.
Popular design themes are also based on a common color, a specific combination of colors, or simply a single favorite plant. These all create a beautiful display when paired with the proper container. Color catches the eye and grabs your attention. Blues and greens soothe and are cool and serene. Reds and yellows create warmth and brightness. Use your favorite flowers, foliage plants and colors. A common and very successful design recipe, commonly called "thrillers, fillers and spillers," combines a tall central focal plant, broad colorful plants around it, and trailing plants to spill over and soften the edges of the container. Strong upright lines suggest vitality; arching lines are restful. A container with a tall central spike, like a Dracaena, surrounded by filler plants such as Lantana or Dragon Wing Begonia and a spilling Scaevola or Potato Vine would create such an effect. When designing, the possibilities are endless. Experimenting with these ideas will allow you to create a unique and personally inspired container.
Many items can be used to grow plants as long as it will hold enough soil and provide necessary drainage. This is a chance to be really creative. An old leaky watering can, tubs, crates, buckets, toys, baskets or an old boot are just some ideas. Any water-tight container could hold a small water or bog garden. The traditional terracotta clay, plastic, resin, metal or untreated wood containers also make wonderful choices.
Whatever the choice, always start with a clean container. If using a previously used pot, wash it first with a solution of one part household bleach to nine parts water. (For example, one-half cup of bleach to 4.5 cups of water.) Since bleach is caustic, wear rubber gloves and avoid spilling on your skin. Bleach also emits harmful fumes, so mix the solution outdoors or in a well-ventilated room.
Most beginning gardeners underestimate the size of the container needed. Be sure to keep in mind the mature size of the plants and their growing habits. A small pot will look completely out of scale as plants fill out and mature. There should be enough room in the planter for at least 3 inches or more of soil under the root balls and for the final soil level to be about 2–3 inches from the top edge to allow for efficient watering.
Remember that containers have different properties. Clay or metal pots dry out very quickly in the summer heat, while glazed ceramic, plastic or fiber, do not. Thus, a terracotta pot might be a better choice for shade, while ceramic or fiber might be better for sun. The type of plant is also a consideration in choosing a container. Cacti from desert areas do much better in porous clay while those from the rainforest ("Christmas cactus" for example) adjust easily to the additional moisture held in ceramic pots. Finally, always consider the weight of the finished container. Plastic containers tend to be lighter than ceramic or clay pots. Placing a heavy pot on casters is a good idea, allowing for easy positioning and moving.
In all cases, adequate drainage is a must. Plant roots exchange gases as part of their life cycle so plants need air around the roots. When the water does not drain readily from the container, it continually fills the soil air pores and the roots cannot "breathe" or exchange gases. The roots will eventually die from lack of oxygen. Add more holes to any pot that does not drain quickly. Add the drainage holes to the sides of the container along the bottom, so that water flows away from the container. Never allow the container to stand in water. Raising a pot off the ground by an inch will help most drainage problems and allow needed air circulation as well.
Good container soil drains freely, is lightweight, and holds adequate moisture. Most container gardeners find that pre-packaged "soil-less" potting mix works best. Typical potting mix components may include peat moss, vermiculite, perlite, bark and polystyrene but not natural soil from the ground. The disadvantage of a potting mix is that it is very light and dries out quickly. The addition of packaged pasteurized "potting soil" to the soil-less mix at a ratio of one part soil to three parts mix will give the soil more weight and allow better water retention. Though helpful, adding potting soil is not required. Soil from the garden is never recommended. It is too dense, compacts easily and will not allow proper drainage and aeration. It may also introduce unwanted elements, such as fungi, soil-borne insects and weed seeds to your container.
Always thoroughly moisten the potting mix before placing it in the container for planting. Place the potting mix in a separate large tub-like container. Gradually add small amounts of water while stirring the soil to thoroughly moisten the mixture. When finished, the mix uniformly should feel moist but not be saturated and should readily crumble in your hand. The organic compounds in the mix absorb water and expand and when there is adequate space retain air pores among the soil particles. This moistening procedure before placing the potting mix in the planting container retains the air porosity in the soil that plant roots require.
Fill the planting container with the moistened mix to within 1–2 inches of the top. There is a common misconception that placing gravel, small rocks or other large grained material in the bottom of the container improves drainage. Actually better drainage through capillary action is achieved by maintaining an even soil particle size from top to bottom. To preserve the air spaces avoid compacting the potting mix when placing it in the planting container. Plants are placed much closer in containers than when planted in the ground. It gives your planter a more mature look immediately.
Create a planting hole for each plant. If using a time-release fertilizer, add it to each planting hole. (See "Fertilizing" below). Note that only time release fertilizer can be added directly to the hole. For any other fertilizer type, follow label directions. When all plants are added, distribute soil so that all plant root crowns are consistent with the level of the container soil. Avoid sunken or protruding root balls. Add additional soil if needed, pat down lightly and water. The soil level will drop a bit when the plants are watered in and settled but this will be minimal if the soil was properly pre-moistened.
Keep the newly planted container in semi-shade for a few days to help the plant become established before placing it in its final location.
Proper watering is essential. Plants in containers dry out much more quickly than plants in the ground. Never underestimate how much a large planter, filled with mature plants, can "drink" on a hot day! Take care; however, as too much water can be just as fatal as not enough, especially if the soil is not well drained. Watering is tricky because it is very weather dependant. Do not water by the calendar. You might not water for days during a cool wet period and then need to water 1–2 times per day on dry, hot days. The amount of sun, soil volume, size, type and location of the planter will all determine when water is needed. Often, the exposed soil surface may be dry but the roots, just inches below, are not. Moisture meters, available at most garden centers, are a great help when deciding when water is needed.
The necessary balance between water retention and aeration can be enhanced by reducing the volume of each watering and increasing the frequency. To reduce the loss of moisture, mulch can be layered onto the soil surface. Another alternative is to place decorative flat pebbles on the soil surface. If you see moisture when you lift the pebble, watering isn’t needed. A drip irrigation system can be a very effective way to minimize watering chores for those with multiple and/or large containers.
Proper fertilizing is another key element keeping your plants looking their best. Potting mixes can vary widely in their composition and nutrient content so it is up to the gardener to thoroughly read and understand the label. Because container plants need frequent watering, existing nutrients are washed away with every watering. The addition of time-release fertilizer (14-14-14 or similar blend) is easy and practically foolproof. Mixed into the soil at planting time or scratched into the soil surface, this product will fertilize your plants all season. Alternatively, fertilizer can be provided by applying an all-purpose water-soluble 15-30-15 or similar fertilizer every two weeks. Please be sure to always follow manufacturers’ directions. When it comes to fertilizing, more is never better.
After resting in the semi-shade for several days, place the finished pot in a place appropriate for the plants it contains. Understanding the terms used to refer to the amount of light, such as "full sun" or "partial shade," is critical in deciding where your plants will grow well. Many survive in places where they do not receive the right lighting, but they may grow etiolated (stretched out, with poor form), fail to bloom, and become easily diseased.
If using a container to brighten a dark or very shaded area of the garden, have two of the same planters and rotate them weekly. Provide the proper light requirements during the off week.
As the plants grow and mature, cut back and remove faded flowers (deadhead) to retain a pleasing size and shape. It look better, promote compact growth, and encourage the plants to bloom longer.
Create your own vision. Container gardening with flowers is an easy, adventurous, flexible, transportable and compact way to indulge your green thumb. The only limits are your imagination.
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