No Drainage Hole Needed
While most house plant growing guides will tell you drainage is key, good drainage is in the eye of the beholder. The goal is to (1.) avoid root rot and (2.) prevent accumulation of unwanted minerals and salts.
- Avoid root rot by using non-soil growing mediums, a robust drainage column, and not letting the water stagnate for too long.
- Use clean water and hydroponic nutrient solution instead of fertilizer. Some cities have unusually clean tap water which can be used un-treated in most cases. Most of us need to use filtered, bottled, or distilled water or meticulously collect rain water.
Creating a Drainage Column
The most important thing in a pot with no drainage is a drainage column. This is basically a space under the soil where extra water collects, but you can do better than just leaving space.
A good drainage column serves several purposes:
- Allows water to drain out of the growing medium, avoiding fungus, bacteria, and other pests that may infest wet soil
- Keeps the roots from sitting in stagnant water
- Keeps the standing water fairly clean and bacteria-free
- Separates the growing medium completely from the drainage area
How to create a drainage column
The best way to set up a good drainage column is by layering various materials with specific purposes. Here are the purposes from bottom to top (starting with 1 for the bottom)
- The bottom-most layer should be somewhat anti-microbial and filtering, to keep the standing water as clean as possible and avoid becoming acrid.
- The next layer should have lots of air pockets and ideally include porous materials that help aerate the water and create a comfortable environment for the roots
- Above the drainage column should be a loose filtering medium that prevents the soil or growing medium from contaminating the drainage column
- Soil or soil-free growing medium comes next. This is where you actually plant the plant.
- Optionally, you may add a decorative or protective layer above the growing medium. This could be moss, decorative stones, course gravel, glass marbles, or just about anything. Or, you can skip this layer.
Material suggestions for each layer
- A tried-and-true option for the bottom layer is horticultural charcoal, and if you want to up your game you can use activated charcoal, but don't use just any charcoal. You may also try perlite, vermiculite, pumice, or another highly porous, anti-microbial substance.
- A favorite primary drainage material is expanded clay pebbles. Other names for this material include "Hydroton" and "LECA" beads. This material is extremely light and strong, does not degrade over time, and may help oxygenate the water. Other options include natural pumice, crushed shells, or even course gravel. Just ensure there is plenty of space for air pockets.
- An ideal filtration material is sphagnum moss because it's light, loose, and extremely resilient to standing water (unlikely to rot or mold). You could also use fabric, fine bark mulch, or get creative. Something like cotton would probably work, or even a discarded window screen.
- For the growing medium, you could use standard potting soil or other organic matter, or something inorganic. Coco Coir represents a likely improvement, because it is less likely to harbor or feed pests, bacteria, and fungi. Mixing coco coir with perlite may represent another level of improvement. You may also experiment with substances like rock wool. While any choice will require plant nutrients, keep in mind that non-soil growing medium is completely devoid of nutrients so you will want to start fertilizing your plant immediately. Standard potting mix may allow you to hold off on introducing plant nutrients. Lastly, remember that any substance you use could turn if left in standing water. Even rock wool can get moldy after it soaks up nutrients or grows algae.
- You can get creative for the top layer. Leave it as just soil, or add something decorative. You can use anything from random organic matter (twigs and leaves) to small sculptures and toys, or even create a mini diorama of a fairy world house and garden, or a hobbit house under a mound. Another option is to add something protective like another layer of LECA or fine gravel or sand. This can help reduce exposure of your organic matter layer to fungal spores, insects that may lay eggs, or other contamination that may come after your plant is planted.
Keeping your plant healthy
So your media are layered and your plant is planted. Now what?
Healthy spider plant in glass container
No plant wants to be over-watered, but especially one without drainage. Most aroids, such as the spider plant pictured above, like to dry out between watering but not be left dry too long. It can be hard to accomplish this without drainage but it is easier with glass because you can actually see the roots. Simply wait until the roots look fairly dry and there is little to no condensation inside the container, then give it a splash. How much depends on the plant and the container, but a good rule of thumb is to leave less than two inches of visible water in the bottom, then wait up to two days for the plant to drink. Some, like the spider plant, will drink up that two inches quickly after they are established in the glass. Others may require that you empty out the excess water after a couple days by turning the whole thing upside down.
For the first few weeks after planting something this way, or until the roots make their way to the bottom of the drainage layer, you must be extra diligent about the standing water. Once the roots colonize the lower drainage layer, they will usually be water-tolerant tuberous roots that will quickly soak up two inches or so of standing water. If they don't, not only could the roots rot, but your growing media or soil could rot from fungi and bacteria.
The water should have a fairly low mineral content, and have added nutrients. Standard house plant nutrient solutions can work for a while but because this setup reduces or eliminates the nutrients available from soil, you should opt for hydroponic nutrients instead. They can be purchased online or at many local stores.