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Vegetable Gardening in Containers

by chuck.mcmullan
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Container gardening is probably the easiest way to jump-start your gardening experience. Contrary to the belief of some, a wide variety of vegetables can be successfully grown in containers. Container gardening seems to make sense if you just want to test the waters and see if gardening is really for you or not. It doesn’t involve digging up large portions of your back yard, and can still offer some great rewards. Container gardens can be grown in a window or door sill, on a patio or balcony, or pretty much anywhere else that receives at least 5 hours of direct light per day. It may be the most realistic solution to a garden if the ground for your garden is not well suited to growing vegetables (bad soil, pests, not enough light, waterlogged, etc.)

Types of Containers

There are many containers suitable for growing vegetables and herbs. Containers for vegetable plants must in general:

  1. Be large enough to support the plant and its roots system once fully grown, trellis or support can be added
  2. Hold an adequate amount of soil
  3. Have good drainage
  4. Have not been exposed to toxic elements

There is an extremely wide variety of containers suitable for vegetables and herbs: Barrels, tubs, boxes, old watering cans, buckets, bushel baskets, terra cotta pots, drums, gallon cans, window boxes, shoes, etc. all can be made into successful container gardens. Pretty much anything that has the capability to hold some soil could be used as a container for gardening. Selecting your container will depend mainly on three factors: size needed (some vegetables need more room), cost, and appearance. Ironically many of the decorative pots available do not have adequate drainage holes, which is a must for the container garden, if choosing something of this sort, make sure to add provisions for drainage. If you intend to build a plating box out of wood, choose a wood that is rot-resistant (redwood or cedar). Standard pressure treated wood is not a good choice for container garden plants, as some of the chemicals used to deter rot and insects are toxic. Liners can also be utilized to improve the life span of wood, assuming they provide adequate drainage.

Size of Containers

The bigger the better. Bigger containers will not dry out as fast, and will offer more room for vegetables to grow. That said, some plants require more room than others, so choose a container size that is appropriate for the particular vegetable that it will contain. Many vegetables don’t do well if their roots are restricted, even if they are well watered and fertilized (this is especially true of squash and cucumbers). Think of the size listed for each particular plant as a minimum, most plants would enjoy a larger container, and it is best to generally avoid containers with a narrow opening. If cages, stakes, or support is needed, provide them while planting seeds, or when the plant is very small to avoid damaging the roots. Cone or pyramid-shaped cages usually work better than the flat type for pots.

Tomatoes, cucumbers, squash, and eggplants require the largest container. Choose something equivalent to a pot with at least a 20-22″ diameter. Peppers, chard, and dwarf tomatoes can be grown in containers equivalent to flower pots with a 16″ diameter. Beets, lettuce, radishes, spinach, and onions can be grown in pots with an equivalent diameter of 6-10″, multiple plants can be grown in each container, assuming the proper spacing is maintained. Most herbs can easily be grown in 4-6″ pots. In general, greens such as lettuce and spinach have shallow roots and can do well in containers that are broader and flatter than the standard flowerpot shape.

Soil

Soil from your garden will most likely not make the most suitable soil for a container. Typically the soil from your garden will have a high concentration of clay, which is too heavy, dense and compact, and will dry out quickly for planting in containers. It also holds too much moisture when wet, resulting in minimal air for the roots, and subsequently encourages root rot. It could also contain many weed seeds or disease organisms, and could be deficient of many of the nutrients your herbs and vegetables will require.

Container gardens require soil that is well aerated, well-drained, and lightweight. This type of soil will allow the veggies to get all of the water and nutrients the vegetables will need. The soil-less mixtures do tend to be lighter, a must if the container is large and expected to be moved from one location to another, otherwise choose an alternative medium. For the do it yourself type, a soil mixture composing of equal parts peat moss, pasteurized soil, vermiculite, and manure would make a good container soil. Make sure you test the pH and add some lime if necessary to bring the pH to about 6.5, or whatever is recommended for the particular species. Vermiculite holds several times its weight in water and nutrients, and keeps the container moist. Prepackaged potting soil available at the grocery store, home centers, and garden centers will likely be the best choice, although probably more expensive than making your own. Many come premixed with a slow-release fertilizer, and some even have extra moisture retention particles, which will help to prevent your plants from drying out on those hot summer days. Hydrogels, or water-holding gels, found in commercial blends of soil mix are starch-based gels that help to retain water within the soil. They swell with moisture and release it when needed. Organic amendments designed to hold water can also have a similar effect and may prevent the need for a second watering on a very hot day.

Water

Because the volume of the soil is relatively small, container plants are susceptible to drying out on a regular basis. Small pots will also have a tendency to dry out faster and will require more frequent watering, yet another reason to choose a larger container. Containers need to be checked for water at least once a day, or maybe even twice on hot, windy days. Stick your finger in the soil, if the soil sticks to your finger, it does not require any water. When watering the plants, water slowly until water begins to drain out the bottom of the container, and avoid getting the foliage wet. If necessary, you could place the containers into a larger container filled with coarse rocks to contain the runoff and allow it to evaporate naturally, a plus for your plants. Just make sure the soil does not have any standing water, and should never be soggy for any period of time.

If the plants are allowed to dry out too much, the feeder roots get damaged, eventually stunting the plant’s growth. Once the plant receives water, the plant spends its energy to repair/replace the damaged feeder roots, and not for producing vegetables, so that energy is essentially wasted.

Adequate drainage is probably the most important thing for your new container garden. Placing some rocks in the bottom few inches of your pot or container should help improve the drainage inside the container. Any rocks will do, the idea is to create some voids to provide a path for water flow. Drain holes are a MUST and are ideally located on the bottom or within the bottom 1/2 ” of the sides of the pot. Remember, the idea of drain holes is to allow excess water to drain, so keep the holes free from external obstructions. For example, a bottom draining pot will not drain well if placed directly on concrete. It would be better if it were raised up an inch or to allow the water to flow freely.

Mulching is a requirement for container gardens. A good layer of mulch will minimize the amount of moisture evaporated through the soil. Compost, straw, pine needles, grass clippings, shredded bark, and leaf mold can all be used as mulches. See the mulch page for more details; all of the information there still applies to container gardening. If the soil is excessively dry, grouping the plants together may offer some benefits. The canopy of leaves will help to shade the soil and pot, which should minimize the amount of moisture evaporated. An automatic watering device may be helpful if you are gone for extended periods, or simply prefer the convenience.

Fertilizer for Container Gardens

Because of the limited volume of soil, container vegetables are more likely to consume the available nutrients, so supplementing with fertilizer is worth considering. Micronutrients will also be washed away through the repeated watering, which is yet another reason to consider adding some supplemental nutrients. A combination of slow-release fertilizer and a weak water-soluble fertilizer is generally recommended when planting vegetables in containers. Chose the fertilizer type that would be best suited to the individual plant. The slow-release fertilizers are typically worked into the soil at the time of planting, and water-soluble fertilizers can be used occasionally all season long (Maybe every 2-3 weeks, depending on the strength). Whatever you choose, read the instructions and measure the fertilizer quantities. Too much fertilizer can be much more damaging than not adding any, so take it on the slow side. A soil tester is also recommended to provide some feedback on the level of fertilizer required.

Sun Light for Container Gardening

Just about every vegetable will produce better in full sunlight, and at a minimum, most vegetables will need at least 5 hours of direct sun. When selecting a location for your container garden, do your best to keep these tips in mind. Generally speaking, leafy crops such as lettuce, greens, and spinach can tolerate more shade than fruit bearing crops – tomatoes, peppers, cucumbers, etc. Root crops are somewhere between the two.

Vegetables for Container Gardens

The best vegetables for container gardens are those with a confined, compact growth habit, such as beets, bush beans, carrots, chard, green onions, peppers, salad greens, spinach, radish, and many herbs. Bush varieties of beans, summer squash, and cucumbers as well as determinate or dwarf varieties of tomatoes, cabbage, peas, and peppers are also recommended. Generally speaking, cucumber, cauliflower, broccoli, corn, potatoes, and vine fruits (especially pumpkins) are tough to grow in containers. Their roots will tend to demand containers that are just not practical. Instead, look for dwarf or compact/bush varieties that are bred for growing in containers in specialty seed catalogs, or graduate to planting an in-ground garden. Most of the smaller vegetables can be planted together in the same pot, as long as the minimum distances are observed for each particular vegetable. You should always plan on starting many seeds, and thinning out the best seedlings so that they are not overcrowded. This has traditionally yielded the best results. You never know how many and which seeds will germinate, so it’s best to plan on some waste.

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