There are so many reasons to consider growing vegetables in containers. No garden space? Use containers on a patio, pool deck or balcony. Crowded garden? Use containers to expand your growing space. Problem soils or drainage issues? Containers allow you to control the media. Your only sunny spaces aren’t garden spaces or your garden space is too sunny for tender veggies? Containers can be located virtually anywhere.
Veggies in containers can be pretty, too. Beverly recently introduced me to a great new term – Ornamedibles. It’s so true! Many edibles have their own ornamental value in our gardens, and others can become ornamental by how we grow them. A tower of green beans, a column of tomatoes, a pot of peppers or eggplants, or a bowl of brightly colored lettuces can stand as equals with many of our favorite ornamental plants.
Containers are their own environment. Everything the plant needs must be provided within that environment. It’s easy to do, but a few key principles and practices must be followed.
Potting media must serve multiple purposes; an anchor for the roots, a moisture reservoir, a nutrient pantry, and an air exchanger. Use a media that meets all of these needs.
Peat or coir based potting “soils” are not the best choices for vegetables. They do not provide any nutrition to the plant on their own and they can break down over a long season, resulting in soggy spots here, dry spots there and poor air exchange.
The best choice is a compost-rich media. You have choices here. Rose soil makes perfectly acceptable potting media for many vegetables. It is a blend of composted top-soil, compost, and minerals. You can also use straight leaf mold compost amended with expanded shale which preserves pore space as the compost decomposes and assists in managing moisture. If you already have a soil free, peat or coir based potting soil that you prefer, you can mix your own media by amending the potting mix with 1/3 to ½ leaf mold compost by volume and adding expanded shale. In all cases, make sure you use the best quality compost you can afford. It is not all created equal.
Vegetable plants in a container will require heavier fertilization than the same plants in the garden. Properly prepared garden soil includes living materials (organic matter), minerals in the soil itself and beneficial microbes that inhabit the Soil Food Web. These things work together to provide the nutrition the plant needs as the roots reach out into the garden soil. Since the reach of roots will be limited to the container, we will need to compensate.
Yes, we can have biologically active, nutritious, living soil in a container. And biologically active, nutritious, living soil results in vegetables that are more nutritious as well. The compost rich potting media we discussed above furnishes a living environment to start out with. Slow release organic fertilizers (SROFs) should be used to keep our media alive and performing well. SROFs provide the major and minor nutrients, minerals, and amendments that nurture the plants and support the microbes in the restricted environment of a container and they do so without burning tender plants.
Follow the directions on your SROF of choice; Arbor Gate Blend and Microlife are good choices. You do not have to increase the amount of fertilizer they recommend, but you should increase the frequency of application.
Water is the ultimate balancing act with containers. Most vegetables prefer evenly moist media. This means that they want moisture on demand, but to never sit in waterlogged media.
Compost rich media with adequate expanded shale added is well-draining by nature. Expanded shale not only provides pore spaces, it is a porous material that absorbs water, releasing it back into the soil as needed. Equal amounts of perlite and vermiculite can be substituted for the expanded shale. Perlite provides the pore spaces while vermiculite holds and releases moisture after you water.
Water your containers thoroughly. Allow the top inch to dry out between watering, but never allow them to dry out completely. The media should not shrink away from the sides of the container at any time. You may have to water your veggie containers twice a day in the peak of summer. Consider adding drip irrigation and a battery-operated timer if your schedule is an issue.
Containers should be matched to the veggies they will hold. They must hold sufficient media to allow full development of the plant and be deep enough to support healthy root growth. It should be stable if you are going to plant tall crops or veggies on supports such as poles or trellises.
The width of the container can be stated as “bigger is better”. Wide, roomy containers will generally hold more soil, give you more surface space for closely spaced veggies, and be quite stable for larger, taller veggies.
The depth of the container is more clearly definable. Lettuce and salad greens can grow quite happily in a container that is 4” – 5” deep. They look their best in low, wide containers that allow for the leaves to expand from the crown of the plant. Bush beans or peas, garlic, onions, radishes, baby beets, and Asian greens such as tatsoi and Chinese cabbage will do well in 6” – 7” of depth. 8” – 9” deep will support eggplant, chard, spinach, medium length carrots, cucumbers, and pole beans. 10” – 12” will provide sufficient root depth for many large veggies such as tomatoes, peppers, okra, squash, sweet potatoes, full-sized carrots and many other root crops.