During my professional career, I have witnessed the emergence and adoption of several production philosophies and technologies that continue to have a significant impact on both hobby and commercial fruit and vegetable production. Some I consider to be of primary importance include organic and sustainable farming practices, plasticulture growing systems including the use of micro (drip) irrigation, high tunnel hoop houses, and permanent raised bed gardening.
One trend I see growing rapidly in popularity is container gardening. More and more commercial growers, as well as home gardeners, are choosing to grow annual and perennial crops, including small fruit trees, in containers.
Just as cold frames (e.g., hoop houses) were used primarily in the nursery industry until they were demonstrated effective in producing vegetables, containers were used primarily in the nursery industry to grow ornamental plant materials until they were demonstrated effective in growing food. The dramatic increase in container production we are currently witnessing constitutes a major paradigm shift in how we grow fruit and vegetable crops.
If you have no experience growing in containers, I recommend visiting with a successful grower before investing in a growing system, especially if you plan on growing commercially. With any new growing system, there is more to it than meets the eye. To assist you in your decision-making process, consider the following.
Many fruit and vegetable crops, from peppers to small fruit trees, can be grown in containers. Consider container type, growing medium and watering needs before investing in a container growing system.
Every container should have drainage holes (preferably along the bottom edge) and be of sufficient size to accommodate a crop's growing requirements. The larger the container, the stouter it will need to be especially if it is to be moved on a regular basis. For growing fruiting vegetables, 5-gallon containers will suffice. Smaller containers are appropriate for leafy greens, herbs and root crops. Dwarf fruit trees are commonly grown in 15-gallon containers. If your goal is to grow a semi-dwarf apple or a standard-size peach tree, a 30- to 50-gallon container would be a better choice. The biggest concern when growing in large containers is weight. A 15-gallon container, including the growing medium, can weigh more than 70 pounds. If in doubt about the container size to use, it's always better to be too big than too small. The larger the container, the less frequent it will require watering.
If you plan on installing a trellis system, consider selecting cylindrical or square-shaped containers. Stakes and cages are more easily attached to a container having a vertical side versus a tapered side. Tapered containers are also more vulnerable to blowing over in a wind storm. Container shape also affects drainage. As a general rule, container height should be equivalent or greater than container width to ensure adequate internal drainage.
For the money, plastic pots offer the best value and are available in multiple sizes. However, not all plastic containers are created equal. Some are made using UV-resistant plastic which gives them a longer service life. Used five-gallon paint buckets and 30-gallon livestock mineral buckets are popular choices for the cost conscious grower. However, these break apart after a few years of sunlight exposure because the plastic is not UV resistant. Also, when exposed to direct sunlight, plastic containers can generate excessive levels of heat which can result in plant stress.
Two nontraditional container systems on the market are Smart Pot® and Air-Pot®. These containers are available in a myriad of sizes to accommodate any crop, including fruit trees. What sets them apart from standard containers is the ability to generate increased rooting capacity. Another advantage the Smart Pot offers is decreased soil temperature, which can reduce plant stress during the summer months. This cooling effect is the product of water evaporating from the porous sides of the container.
An ideal growing medium should be well drained while also able to retain sufficient water to reduce the frequency of watering. It should also be free of weed seed and diseases, and it should be heavy enough to prevent frequent tipping over but not too heavy as to limit handling. For this reason, garden soil should not be used exclusively as a container growing medium.
A good growing medium for both vegetable and fruit production should consist of inorganic and organic components. Some of the inorganic components include perlite, vermiculite, builder's (coarse) sand and weathered granite. Some of the more popular organic components include peat moss, coir (coconut fiber), pine bark and compost. Pine bark used in a growing mix should be small with the particles measuring no larger than a 3/8-inch diameter. The proportion to use in a mix can vary depending on the availability, cost, crop to be grown and container size.
Packaged growing mixes are a good choice when only a few containers are involved. Avoid purchasing mixes containing only peat and vermiculite or perlite, aka "peat-lite." These seedling mixes are not a good choice for use in large containers as they don't have the bulk to support large plants. Packaged growing mixes containing a large proportion of composted pine bark are a better choice for use in large containers. These denser mix types are commonly advertised as nursery mix, planting mix or potting soil. For more extensive container gardens, the expense of prepackaged mixes may be quite high. A growing medium for vegetables can be made by mixing equal volumes of peat moss, aged pine bark, perlite and washed builder's sand. A good container mix for growing fruit trees consists of four parts aged pine bark, two parts builder's sand, two parts perlite and two parts compost.
Most packaged growing mixes come with enough fertilizer blended in to get a crop off to a good start. Some growers choose to add a slow release fertilizer at planting, based on label recommendations. A supplemental liquid fertilizer can be applied on a weekly basis if needed.
Growers making their own mix will need to submit a sample for testing. Ideally, the mix will have a pH between 5.5 and 7.0, and a salinity reading between 1 and 5 millimhos. Mixes containing a high percentage of bark or peat tend to be acid in reaction. Lime can be added to reduce acidity. Mixes containing a high percentage of compost, especially manure-based compost, will tend to have high levels of soluble salts. The addition of fertilizer to compost-based growing medium can increase the salinity level. Therefore, a growing medium registering excessive soil salinity should be leached heavily prior to planting and fertilizer application. Soil testing will also reveal any nutrient deficiencies.
Expect to water more frequently if you choose to grow in containers made with porous materials such as wood, clay or fabric. With each irrigation, apply water until it begins to exit the bottom of the container. Overwatering wastes water and nutrients via leaching. The growing medium should always be moist but not soggy. Hand watering is fine for a few containers, but a micro-irrigation system is recommended for a commercial system. For containers with a capacity of 5 gallons or less, a single dripper per container will suffice. For larger containers, drip rings or spray stakes enable more uniform coverage. If you choose to automate your irrigation system, the timer will need to be adjusted on occasion to match the water requirements of a maturing crop and changing weather conditions. Most container-grown plants will require daily watering during the summer.
There are plenty of things to consider before deciding to install a container production system. Hopefully, this overview has provided enough basic information to help you decide if container production is something you want to pursue.