Good planter mix should hold enough water for adequate root growth and allow excess water to drain easily from your planter.
It should also contain enough nutrients to steadily nourish your plants through their growing season. Soil-based mixes contain some real soil and are slightly heavier. 'Soil-less' mixes contain peat or vermiculite, are lighter, and may dry out more quickly. These mixes are designed for optimum drainage in garden planters, but may require more frequent watering.
Soil-less mixes are a good choice for annuals, but some soil should be added to garden planters growing perennials, shrubs or trees. Adjusting your potting soil mix may be required to allow for weight, the type of plants or the watering requirements of your plants.
Mixing your own growing media for your garden planters can be cheaper than buying pre-mixed commercial blends - plus it allows you to adjust your mix to meet your plant's specific requirements.
Every planter mix or potting soil should include the following components:
A simple lightweight blend is 1 part organic, 1 part inorganic, with a splash of nutrients. Experiment and watch your plants to know if they like the mix.
Water-absorbing polymers may be added to the soil mix in your planter to improve water-retention.
Alternatively a good mix includes 1 part topsoil, 1 part peat moss and 1 part perlite. Never use the soil out of your garden as it tends to harden into 'concrete' in a garden planter and may be home to unwelcome pests or diseases.