How to Make a Self-Watering Planter From a Plastic Bottle

A self-watering planter keeps soil evenly moist by drawing water up from a reservoir through a wick. It is ideal for herbs and salad greens on a windowsill, for people who travel, and for anyone who tends to forget watering. This version uses a single plastic bottle and a strip of old fabric, and takes about fifteen minutes to make.

How wicking works

Water moves through fabric and soil by capillary action, the same effect that lets a paper towel soak up a spill. When the soil dries, it pulls more water up the wick. When the soil is moist, the flow slows down. The result is steady moisture without waterlogging, which is exactly what most herbs and leafy greens want.

What you need

A clean plastic bottle of 1.5 to 2 liters. Thicker, rigid bottles are easier to cut.
A strip of cotton or wool fabric about 2 centimeters wide and 20 centimeters long. Old t-shirts, socks or cotton shoelaces work. Synthetic fabrics wick poorly.
A utility knife or sharp scissors.
A nail or skewer, heated, or a small drill bit.
Potting mix, with a handful of perlite or coco coir mixed in.
A seedling or seeds.
Optional: a paper bag, paint or tape to cover the reservoir.

Step-by-step

Clean the bottle and remove the label.
Cut it in two about one-third of the way down from the top, just below where the shoulder curves in. The top section will hold soil and the base will hold water.
Make a hole in the cap about 5 to 8 millimeters wide using a heated nail or drill bit. Be careful with hot metal and do this in a ventilated space.
Thread the wick through the cap so that about 8 centimeters hangs below and the rest sits above. Tie a knot above the cap if it slips.
Screw the cap back on and turn the top section upside down, so the neck points into the base.
Check the fit. The neck should sit above the bottom of the base, with the hanging wick reaching close to the bottom.
Fill the top section with damp potting mix, coiling the upper part of the wick inside the soil rather than leaving it pressed against the side.
Plant your seedling or sow seeds.
Water from the top the first time until water drips through into the reservoir. This starts the wick.
Fill the base with water to a level just below the neck.

Steps to build a bottle planter — Cut, flip, thread and fill.

What to grow

The planter holds a small amount of soil, so choose compact plants with moderate water needs.

Works well	Avoid
Basil, parsley, chives, mint	Rosemary, thyme, lavender (they prefer to dry out)
Lettuce, arugula, spinach	Tomatoes, peppers, squash (too big)
Green onions, microgreens	Succulents and cacti (too much moisture)
Pothos and other easy houseplants	Plants with deep taproots

Herbs that like dry roots, such as rosemary and thyme, are better in a terracotta pot, as explained in our balcony herb garden guide.

Care and maintenance

Refill the reservoir when the water level drops close to the end of the wick. In warm weather that might be every few days; in cool weather once a week or less.

Flush once a month by watering from the top until water runs through, then empty and refill the reservoir with fresh water. This prevents a buildup of salts from fertilizer and tap water.

Feed lightly. Add a very diluted liquid fertilizer to the reservoir every two to three weeks, at about half the normal strength. Compost tea diluted 1 to 3 works well.

Stop algae. Light reaching the water in a clear bottle encourages green algae, which can smell and clog the wick. Wrap the base with paper, tape, an old sock or paint it a dark color.

Troubleshooting

Soil stays dry even though the reservoir is full. The wick may be too thin, synthetic or not touching enough soil. Replace it with a thicker cotton strip and make sure the top part is buried in the mix. Water from above to restart the flow.

Soil is soggy and smells. The wick is too thick for the plant, or the reservoir is too full and touching the neck. Lower the water level so only the wick reaches it.

Fungus gnats. These tiny flies breed in constantly wet soil surfaces. Add a thin layer of sand or fine grit on top of the soil and let the surface dry slightly.

Make it bigger

The same principle works at a larger scale. Two food-grade buckets nested inside each other, with a wicking cup or a fabric wick between them and an overflow hole drilled in the outer bucket, make a self-watering container big enough for tomatoes and peppers. A vertical row of bottle planters can also be hung on a wall, as described in our recycled vertical garden guide.

A bottle planter will not last forever. Plastic in sunlight becomes brittle after a season or two. When that happens, recycle the bottle if your local program accepts it, and make a new one with the next bottle that comes into the house.