Garden planters require adequate drainage to keep plants healthy
Drainage is the one feature that cannot be over-looked or compromised
When purchasing your outdoor planters, the very first thing to do is ensure there are holes for drainage. If the container does not already have holes, determine if you can safely drill holes to create adequate drainage.
Avoid ceramic or metal planters without drainage holes as it is extremely difficult to drill the holes yourself without damaging or breaking the planter…and often very costly to have someone drill them for you. It is always best to purchase planters and windowboxes than come with adequate-sized drainage holes already in them.
Adding materials such as clay shards, coarse rocks, packing ‘popcorn’ (styrofoam’) or charcoal will help to prevent water pooling and encourage drainage at the base of your garden planters, but adding these materials does not take the place of proper drainage holes.
Use Soil Mixes for Container Gardening
In addition to ensuring the planter you use has proper drainage holes, be sure to use a soil or soil mix designed specifically for container gardening. This soil is composed of materials that encourage good drainage and will not harden to ‘concrete’ in your planter as the growing season progresses.
You will also find special additives designed to keep planter soil aerated. Add coir or moss liners to hanging baskets and wall planters to help discourage soil from running right through the drainage holes during watering.
The only recommended way to use that lovely garden planter on your balcony that doesn’t have drainage holes is to use it as a ‘cache pot’. Placing a planter with drainage inside one without, works well—as long as you provide some way for air to circulate at the base, and you watch closely that excess water does not pool at the base of the cache pot.