Planter box gardening offers a practical solution for cultivating plants in compact urban spaces like balconies, patios, and decks. The controlled environment of a container allows gardeners to circumvent issues like poor native soil or limited ground space, making fresh produce and vibrant flowers accessible. Success begins with a careful selection of plants that can thrive within the confines of a box, paired with an understanding of the environmental conditions of the specific location. Choosing the right plant varieties for the available volume of soil is the first step toward creating a productive and visually appealing container garden.
Essential Factors for Selection
The physical limitations of the planter box and its location are the primary constraints that dictate viable plant choices. Container size, particularly depth and volume, is directly related to a plant’s root system needs; a container that is too small will restrict root growth. Shallow-rooted plants, such as most herbs and greens, can manage well in containers as shallow as six to ten inches. Larger vegetables like tomatoes require a depth of at least 15 to 20 inches to support their extensive root structure and mature size.
Sun exposure is another factor influencing plant selection, as most edible crops require a minimum of six to eight hours of direct sunlight daily. If the planting location receives only partial shade, select plants that tolerate lower light, such as hostas or certain leafy greens. All planter boxes must also have adequate drainage holes to allow excess water to escape, preventing the anaerobic conditions that cause root rot.
Recommended Edible Crops
Planter boxes are effective for growing certain edible crops, provided you select varieties bred for compact growth and match them to the correct container size. Fast-maturing crops and those with shallow root systems are well-suited for container gardening, offering a quick return on effort. Leafy greens like lettuce, spinach, and arugula can be grown successfully in small, shallow containers, often requiring a soil depth of only six to eight inches. These “cut and come again” plants are productive and can be harvested repeatedly throughout the growing season.
Root vegetables like radishes and carrots require a container depth that exceeds the mature length of the root, often twelve inches or more for standard varieties. For high-yield favorites, select bush or dwarf cultivars, such as ‘Patio Hybrid’ or ‘Tiny Tim’ tomatoes, which are determinate. A single dwarf tomato plant can thrive in a five-gallon container, while full-size tomato plants demand a 10-gallon container or larger to support their fruit production.
Peppers, both sweet and hot varieties, grow upright and are naturally more compact, making them ideal container plants that generally require a five-gallon container per plant. Herbs are another excellent option, with basil, chives, and mint growing well in smaller pots, often ten inches or less in diameter. Bush beans are preferable to pole beans as they do not require extensive vertical support and yield heavily in a smaller footprint.
Ornamental and Decorative Plants
Planter boxes can host a vibrant display of ornamental plants that offer continuous color and interesting textures. Annual flowering plants are a popular choice because they provide season-long blooms and can be easily changed out each year. Petunias and marigolds are reliable annuals that tolerate full sun and heat well. Calibrachoa, often called ‘Million Bells,’ is a vigorous annual known for its continuous, small, petunia-like flowers that require no deadheading.
Trailing plants are an effective element to add visual flow and soften the edges of the planter box. Sweet potato vine is favored for its striking foliage, available in colors from chartreuse green to deep purple, and its rapid, trailing growth habit. Wave petunias are a trailing annual that produces many blooms, creating a colorful, spilling effect. For shaded planter box locations, perennials such as hostas offer lush, textured foliage and thrive in lower light conditions.
Soil, Watering, and Maintenance
The confined environment of a planter box necessitates specific maintenance practices. Container gardening requires the use of a lightweight, well-draining potting mix, which is distinct from dense garden soil. Potting mix is typically a soilless blend of materials like peat moss, coir, perlite, or vermiculite, designed to provide adequate aeration and drainage while retaining moisture. Using native garden soil is not recommended because it compacts easily in a container, restricting the flow of oxygen and water to the roots.
Nutrient depletion is a challenge in planter boxes, as regular watering causes nutrients to leach out of the soil more quickly. Potting mixes often exhaust their available nutrients within six weeks, requiring a consistent feeding schedule. Gardeners should use a balanced, slow-release fertilizer mixed into the soil at planting and supplement with a water-soluble liquid fertilizer every one to two weeks during the active growing season.
Watering must be deep and thorough to ensure moisture reaches the entire root zone. Container plants, especially those in smaller boxes or exposed to full sun and wind, may need watering at least once a day, and sometimes twice during periods of extreme heat. The goal is to maintain even moisture without allowing the soil to become waterlogged. Check moisture levels by inserting a finger two inches into the mix; if it feels dry at that depth, it is time to water again.