A self-watering planter, often termed a sub-irrigation planter (SIP), simplifies plant care by providing a consistent water source from below. This system relies on capillary action, or wicking, to move moisture upward from a reservoir directly into the soil. Instead of traditional top-down watering, the plant roots draw water as needed, promoting steady growth and reducing the frequency of manual watering. This DIY approach allows gardeners to create efficient containers using common materials.
Necessary Components and Tools
The foundation of this system requires two containers. The outer container serves as the water reservoir, and the inner container holds the growing medium and the plant. The inner container must be slightly smaller than the outer one to allow for a gap at the bottom where the water collects. Durable wicking material transports water upward; options like nylon rope, synthetic felt strips, or cotton mop strands resist rot and maintain structure when wet. Tools include a drill with a 1/4 inch to 1/2 inch bit for creating drainage and wick holes in the inner pot. A utility knife or heavy-duty scissors will also be necessary to cut the wicking material.
Step-by-Step Construction Guide
Begin by preparing the inner container by creating several drainage and aeration holes around the sides. Use the drill to place these holes approximately one to two inches from the bottom rim to prevent the soil from becoming saturated and allow for necessary air exchange. Next, locate the center of the inner container’s base and drill one larger hole for the wicking material to pass through.
Cut the chosen wicking material to a length that allows it to extend from the center hole to the very bottom of the outer reservoir, plus a few extra inches. Thread one end of the wick up through the base hole of the inner container, ensuring a few inches of material remain inside the container to contact the soil. The rest of the wick should hang freely below the base.
To simplify watering, creating a separate fill tube is recommended for easy access to the reservoir. This tube, which can be PVC pipe or an old plastic bottle with the bottom removed, allows water to be added directly without disturbing the soil. The tube should be tall enough to reach from the reservoir bottom to just above the soil surface when assembled.
Place the inner container inside the outer reservoir, making certain the wick hangs down and touches the bottom of the outer container. The top edge of the inner container should sit slightly below or flush with the top edge of the outer container, depending on the specific design. Position the fill tube so that its opening sits on the floor of the outer container, resting right next to the wick.
An overflow hole is necessary to prevent excessive watering from drowning the roots by establishing the maximum water level. Drill a small hole in the side of the outer reservoir, about one-third of the way up from the bottom. This ensures the water reservoir never rises into the soil level.
Preparing the Planter for Use
The success of the self-watering system hinges on selecting the correct growing medium, which must facilitate capillary action. Standard garden soil or heavy topsoil is unsuitable because its fine structure compacts easily, inhibiting the upward movement of water. Instead, use a lightweight, porous potting mix that is primarily peat moss or coir-based, as these components hold moisture while remaining well-aerated.
Carefully fill the inner container with the chosen potting mix, ensuring the soil is packed firmly around the portion of the wick that is inside the pot. This firm contact is necessary to establish the initial pathway for water to travel from the wick into the soil column through capillary action. Do not press the soil down excessively in the rest of the container, as this can impede aeration and healthy root growth.
After adding the soil, the system requires complete initial saturation through top-watering to properly activate the medium. Pour water over the top of the soil until it runs freely out of the overflow hole and the drainage holes in the inner pot. This heavy watering ensures the entire soil column is fully hydrated and that the capillary bridges are established.
Once the soil is saturated, the water reservoir can be filled, typically through the installed fill tube. Add water until it begins to exit the overflow hole you drilled, which confirms the reservoir is at its maximum safe level. From this point forward, the planter only needs to be watered by refilling the reservoir when it runs low, not by watering the soil surface.
This watering method is beneficial for plants that require consistently moist conditions, such as high-water-use annual flowers and leafy vegetables. Herbs like basil and mint thrive in SIPs, as do common container-grown vegetables like tomatoes and peppers. Plants that prefer drier conditions, such as succulents or cacti, are not suitable for this system due to the constant moisture level.