Not sure what to use for drainage in pots? In this article, you'll learn what to use for pot drainage, which to avoid, and why some popular pot drainage methods are really bad for plants.
Drainage is very important for the health of plants grown in pots. For example, root rot, a common but deadly disease in potted plantsOverwatering or waterlogged soil, can be easily prevented if proper drainage techniques are implemented.
There are several proven methods to increase soil drainage in potted plants. Fortunately, implementing these techniques does not require a college degree in horticulture.
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What to use for drainage in pots
Before we get into what to use in a pot to help with drainage, it is only appropriate to address the "myth" of using pebbles, gravel, rocks, pot shards or sand in pots. In reality, the widespread practice of placing them under potting soil is bad for proper drainage.
Various studies from several universities show that these so-called drainage materials for pots actually inhibit the movement of water from the potting soil through the drainage holes. Even the supposed side benefit of preventing critters from getting into the pot through the drainage holes is marginal at best.
The science to support this claim has been around for almost a century now. But somehow gardeners ignored it and stuck to the practice of using these drainage materials in pots.
The bottom line is that these drainage materials in pots encourage waterlogging of the potting soil! This is ironic as the whole point of lining flower pots with rocks, pebbles, gravel, sand etc. is to prevent the potting soil from getting soggy.
Here is the linkon such a study by Washington State University, which links to an earlier study. The University of Illinois Extension website also has a report throwing this practice under a bus.
If using all of the popular potting soil drainage materials isn't ideal, then what should gardeners use for their pots?
What can you use for drainage in pots?
Deciding what to use for drainage in pots is more about optimizing drainage in potting soil or potting soil. That means good drainage holes at the bottom of the pot are the center of effective pot drainage.
Below are some materials that you can add to your potting soil so that you don't end up with soggy soil in your pots. The first three are about soil improvement. This essentially means they are added or mixed into the potting soil to improve drainage.
All soil improvement techniques involve repotting the soil. Typically this means emptying the potting mix into a large container, adding the soil amendment, mixing it very well and finally adding the modified or upgraded potting mix back into the pot.
Perlite is an important ingredient used in the manufacture of potting soil for growing plants indoors. It is a lightweight, extremely porous material made by applying heat to volcanic silicate rock at temperatures north of 1500°F.
This thermal treatment converts the water in the rock into gas. The end product is a lightweight, soft, off-white material that is also popular in hydroponics.
Adding perlite to potting soil would create tiny air pockets in the soil. This keeps the soil loose, which inevitably promotes efficient water drainage.
A potting soil or potting soil should already contain perlite. But if you are unhappy with the drainage, you can simply buy something and use it to improve the soil to rectify the situation.
Like perlite, vermiculite is an important component of good potting soil. They are sold commercially as light, glossy flakes with colors ranging anywhere from sandy brown to dark gray.
The highly porous nature of vermiculite makes it a very good drainage material for pots. In potting soil, however, their main function is to improve moisture and nutrient retention. And it is also used to stabilize soil pH due to its pH buffering ability.
Horticultural grade or washed sand is widely used in nursery mixes and greenhouses. When used to improve potting soil, it not only improves drainage but also helps stabilize the pot with the increased weight. This is important for outdoor plants as the increased weight prevents strong winds from blowing them away.
Considered to be the ideal soil drainage supplement for succulents and cacti, the recommended size is between 0.25mm and 2mm. Also, the absence of impurities like silt and clay is an added benefit of coarse sand for changing potting mixes.
However, not all coarse sands are ideal for this purpose. The best and purest source of coarse sand is deeply mined mountain sand. Because of their high pH, you must avoid sands made from shell fragments, skeletons of marine organisms, and coral. You should also stay away from sand from the sea due to the presence of sea salt which is detrimental to crops.
Use a smaller pot
This "pot-in-pot" potting soil drainage technique is usually recommended if you intend to grow plants in a decorative ceramic or terracotta pot where drilling drainage holes is impractical.
With this technique, the smaller plant pot with drainage holes is placed in the larger decorative pot. For this to work, the larger pot should be big enough so that the water that collects in it doesn't come into contact with the plants in the small plant pot.
A plastic container can also be used as a planter. The only requirement is that it must have drainage holes and be completely covered by the decorative pot to maintain the integrity of the larger pot as a decorative piece.
In order for it to work consistently, you would need to check the water level in the large pot regularly; Simply pour out the water when the water level is more than a few inches from the bottom of the pot
A major problem with growing plants in a pot is to mitigate or even completely prevent water from washing out the soil through the drainage holes.
You can prevent soil from leaking out by placing coffee filters over the drain holes to ensure only the water is filtered out. The coffee filters don't allow for drainage in pots so much as a medium to ensure you don't gradually deplete your precious potting soil as you water.
If coffee filters aren't available, a great substitute is cheesecloth placed over the drain holes.
How to ensure proper drainage in pots
While improving potting soil is a great way to ensure good drainage in pots, there are several things you can do to ensure proper drainage. Implementing the recommendations below may eliminate the need to either change the soil or worry about what to use for drainage in your pots.
- All your pots, except decorative pots, must have holes in the bottom to prevent excess water from remaining in the pot.
- Always check if the drain holes are clogged. Sometimes clogged holes are the reason soil isn't draining properly.
So before you do something as extreme as repotting and changing the soil, clean out the holes first. This could be the solution to your drainage problem.
- Drain holes are sometimes blocked by the soil below. This problem is more common when the pot is placed on a non-concreted surface.
The solution is to place the pots on a raised platform so the holes are not obstructed. If that's not possible, drilling holes on the sides near the bottom of the pot is another option.
- Remove any drainage materials at the bottom of the pot if you have any already placed there. As previously mentioned, drainage materials actually impede the downward movement of water.
Be sure to clean the pot thoroughly after removing the drainage material before replanting your potting soil.
- Always use very high-quality potting soil as a growing substrate. For potted planters, this is just as important as drainage holes.
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