After choosing the planter you need to choose the best soil mixture for your planter. You can choose to buy a soil mixture or you can make it yourself. Why do you need to use a soil mixture for planters? The main reason for this is that these mixtures contain additives which are needed to increase the absorption of moisture and retention. Watering planters can also result in a decrease of nutrients in the soil. Adding a soil mixture that contains fertilizers that are released slowly will tackle that problem.

Buy a soil mixture
The following soil mixture can be used in planters that move the moisture upwards through the soil from a built in reservoir.
Container Mix.
Self-Watering Container Mix.
Container Booster Mix.

Make a soil mixture yourself
The most important specifications for soil are that they are light, friable, well drained and moisture-retentive. If you are using normal garden soil you can get diseases and problems with insects in your planter. Here are three well known soil mixtures you can make yourself:

Organic Blend: 5 gallons finished compost, 1 gallon builder’s sand, 1 gallon vermiculite or perlite, 1 cup granular, all-purpose organic fertilizer.
Standard Blend (Cornell Mix): 1 bushel vermiculite, 1 bushel ground sphagnum moss, 8 tablespoons super phosphate, 8 tablespoons ground limestone, 2 cups bone meal.
Light Blend (for rooftops): 5 gallons ground sphagnum moss, 5 gallons vermiculite or perlite, 2 gallons compost, 1 cup granular all-purpose organic fertilizer.

Always use a nutrient rich potting soil for your planters. This potting soil exists of a mixture of coir fiber, compost and vermiculite.

Coir
You can buy coir also in dry bricks. You can soften them with warm water before you use it. The advantage of coir is that it is Leigh weighted, it is easily rewettable and that it does not decompose easily when you mix it. However, the disadvantages are that coir may contain a high salt level and that it does not contain any nutrients.

Vermiculite
You can describe vermiculite as a silicate mineral that consists of thin plates. Vermiculite is heated to a high temperature. The advantages of vermiculite are that it holds water and fertilizer. Another advantage is that it is lightweight and that it allows the roots to breath. The down side is that it can hold too much water resulting in drowning your plants.