Drainage Do or Die

Why is drainage so important? We have a saying in our office, “You can plant in just abut anything as long as it has drainage.” The reason why drainage is important is that most plants don’t like their roots to sit in water, and without drainage, water build-up in containers is likely. Although plants use their roots to take in water, too much water will lead to root rot, which kills off the roots and eventually the plant. Surplus water also results in a lack of air flow around the roots, preventing them from absorbing oxygen, which is also imperative for plants to survive. Let’s look at drainage do or die!

The Importance of proper Potting Medium

The type of potting soil used in your container plays the most important role in proper drainage. Some mediums retain more water than others. This is why it’s important to understand how it works and what will work best for your plants.

The Science Bit

When you water a pot plant from above, the water drains through the soil and out the bottom of the pot through drainage holes. This is thanks to gravity. A good potting medium will include water-retaining materials so that some water is held in place for use by the plant’s roots at a later stage. If your potting soil contains very fine particles and a small proportion of air spaces, the water can ‘wick’ upwards by what is called capillary action. When this upward force is greater than the downward gravity, it creates a ‘perched water table’ at the bottom of the pot that doesn’t drain out. The water sits there and causes the pot to become waterlogged – a death sentence for your precious plant.

3 ways to improve drainage in potting medium

As we discuss above, smaller particles in the soil can result in poor drainage, so it stands to reason that increasing the air space between the particles decreases the plant’s ability to wick upwards, and therefore increases drainage. These are three mediums you can add to your potting medium to improve drainage:

1. Perlite: This lightweight, porous material is in fact a volcanic silicate rock that has been heated to very high temperatures until it popped like popcorn and increased its size between 4 – 20 times. When added to potting soil, this non-toxic material improves aeration and drainage, has a low-water holding capacity and comes at a reasonable price.
2. Vermiculite: Another lightweight porous material, vermiculite is made by heating chips of layered mineral mica to very high temperatures, causing the material to expand. It works the same way as perlite to improve aeration and drainage but also has some potassium, magnesium and calcium content, and has a high water-holding capacity that can retain water, nutrients and air for use by the plant’s roots.
3. Silica Sand: Sand is one of the basic materials, composed mainly of small particles of silica that do not absorb water. It is often added to soils for propagating cuttings and is a better option for succulents and cacti. It will behave in a similar fashion to the other media on the list, but has very low-water-holding capacity and is the cheapest amendment material. It is heavier and creates less aeration, but still works.

READ MORE: What is potting soil?

Hacks to cover drainage holes in pots

1. Use old sponges at the bottom of the pot before adding the soil. These soak up the water and holds it so it keeps the soil most for longer. They prevent water from flushing out the bottom of the pot but also doesn’t allow the roots to become waterlogged.
2. Use a coffee filter to create a permeable barrier between the soil and the drainage holes. This allows the water to pass through but retains the soil.
3. In large pots, use empty plastic bottles to fill space the bottom of the pot before adding the soil. This reduces the amount of soil needed and makes the pots less heavy. 
4. Packing peanuts or Styrofoam beads make great drainage materials. They are light and perfect for large pots to create that drainage layer above the drainage holes. 
5. Cut a piece of shade cloth into pieces to cover drainage holes and keep the soil in the pot.

READ MORE: Take a look at these beautiful African Houseplants