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Jun 29, 2023

Wick Watering: Simple and Efficient

Use wick watering to keep your plants hydrated. Self watering wick systems are

Use wick watering to keep your plants hydrated. Self watering wick systems are simple to assemble, and they use less water than other methods.

Wick watering is a lesser-known method of efficient irrigation. I was first introduced to the concept while reading a paper from India many years ago, in which wicks were used in conjunction with buried clay-pot irrigation. I later discovered a variety of systems for wick watering that had been used in lab studies to measure water use, vacation-water plants, provide a steady water supply for plants in greenhouses, and starting seeds. I couldn't find any research on the use of wick irrigation in the field or garden, so I gave it a try. Over the past 30 years, I’ve conducted many experiments and field trials that have helped me understand how to design and use self-watering wick systems.

Wick irrigation uses a wettable fabric or rope to carry water from a reservoir or pipe to the roots of a plant. Wick watering can work by capillary flow that goes up and over a rise, resulting in a slow flow; by gravity flow, where water runs down the wick, which produces a fast flow; or by a hybrid of both systems. Here's a closer look at both techniques so you can determine which will work best for your plants.

With capillary wicks, the water rises through small channels in the wicking material. In one test I performed, water in a 7/16-inch washed solid-braid nylon rope rose 10 inches in 100 minutes and 22 inches in 20 hours.

Capillary irrigation commonly uses a self watering wick with one end in a water reservoir beside a plant and the other in the soil, meaning the wick has to rise out of the reservoir and bend over into the soil. This can also be done with a wick that rises from the reservoir under a plant through a hole in the pot.

At the University of California, Riverside, I studied a palo verde tree seedling (Parkinsonia florida) using a capillary wick from a reservoir underneath the plant. The seedling grew in a bucket of pure 16-grit silica sand. After one month, the plant was still growing and exhibited no sign of water stress with water consumption of less than 2 tablespoons a day.

Gravity wicks work similarly to capillary wicks, but the flow is downward. (For example, a reservoir sitting on the ground next to a plant, with the wick running out of the bottom of the reservoir and down to the roots belowground.)

In a test I performed with new 7/16-inch solid-braid nylon rope (washed once with hot water and detergent to remove lubricants used in weaving), the flow rate with the rope inside a snug-fitting plastic tube was 0.6 milliliter per second — compared with 1 milliliter per hour with capillary flow. Water in a gravity nylon wick ran 12 feet down a vertical wick in just 15 minutes. Long gravity wicks like this may make it possible to encourage deep rooting in plants, allowing the roots to contact groundwater at 10 to 15 feet.

Field trials in the Sonoran Desert demonstrated the value of gravity wick irrigation in arid climates, using a hose clamp near a 5-gallon reservoir to adjust water flow. After receiving less than 30 gallons of water, all tested plants remained alive and well after three years. This compares with water use that might’ve surpassed 360 gallons for the same period.

To fashion your own wick watering system for either potted or in-ground plants, first gather the basic materials: wick, clear plastic tubing that the wick will fit snugly in, and a water reservoir. For gravity wicks, you’ll also need a hose clamp and a barb-to-thread fitting to attach the plastic tubing to the reservoir. If you can't find a barb-to-thread fitting at your local hardware store, you can order one online. You’ll also need a drill, a spade bit sized to the barb-to-thread fitting, and polyurethane glue.

I prefer 7/16-inch or 1/2-inch solid-braid nylon rope, but polyester and other fiber tapes and ropes may work. Cotton wicks were traditionally used in India, but I’ve found nylon and polyester braided ropes are less likely to get moldy and clog when used for wick watering. Polypropylene and many mixed-fiber ropes don't work. Wash the rope with detergent or soap and rinse it well before use. If you wash it in a washing machine, use a mesh bag or tie it in a pillowcase to avoid rope tangles. You can easily test capillary rise, gravity flow, and wetting rates in wick materials by hanging the wicks so their bottoms are in a container of water colored with food coloring. Track the rate of water rise to determine which wick will work well for your needs. The water should rise rapidly up the wick.

For a reservoir, recycled containers work well, such as old soda bottles and plastic jugs, as do 5-gallon buckets. Polypropylene containers will last for years, but polyethylene may only last a season. In high-wind areas, you may need to stake or tie the reservoirs down to keep them from blowing away.

Capillary wick systems work well for tending house plants. These self watering wicks are easy to set up at home and good for vacation-watering. For this, all you need is a wick, a bit of plastic tubing, and a reservoir. Simply run your wick through the tubing (which helps reduce evaporation), and then stick one end in the water and one end in your plant pot. You can push the end of the wick down into the container with a stick or screwdriver.

For a gravity wick system, drill a hole in the side of your reservoir, close to the bottom. (Put masking tape over the spot before drilling if the plastic is thin. This will help prevent cracking.) A spade bit with spurs will make cleaner cuts that provide a better seal. Then, put polyurethane glue on the threads of your barb-to-thread fitting and screw it into the hole. You may need a wrench to get it properly tightened. The glue will help strengthen and seal the joint. Thread your wick through the vinyl tubing, and attach the tube to the end of the fitting. Attach the hose clamp to the plastic tubing so you can control the water output in your new self-watering wick.

For in-ground plants, place the wick in the planting hole as deep as possible. Add several gallons of water and let it drain. Then, add the seedling with roots near the wick, and backfill the hole with soil. Compress the soil to avoid air pockets. If you want to get more detailed with your irrigation setup, you can use a multiple-wick arrangement for root pattern development that will help improve a plant's wind-firmness.

You can also develop a catchment system for wick irrigation that uses rainwater. Australian orchardist Preslav Trenchev figured out a great way to water trees with rainwater, self-watering wicks, and plastic sheets. Trenchev devised a pocket reservoir and catchment by shaping the soil and fitting a plastic sheet around a tree (see photo above). Then, rainwater can be stored in the reservoir and fed to the tree by wick. The commercial product Groasis Waterboxx achieves a similar effect.

Give self watering wicks a try — I think you’ll like the results. Wick watering can be a valuable tool for gardeners, orchardists, and farmers. The systems are robust and low-cost, and they offer a long refill interval. Beyond its use in the average garden or field, wick irrigation can also play a role in tree planting to sequester carbon, and in growing vegetables with less water in the most challenging environments. And the possibilities don't end there: We can develop better wicks for different uses and understand the best uses of capillary and gravity-fed wicks. As we continue to look for ways to secure a better future for our gardens and our planet, this technique shows promise.

Who doesn't love a hanging basket of flowers? But keeping them healthy can be a challenge, because they’re exposed to the sun and wind, and the hanging factor can make them difficult to water. Adding wicks to a hanging basket makes it easier to maintain your flowery finery. Start by obtaining wick material and a hanging basket with an integrated reservoir. The basket may come with a wick already in place, but you’ll likely need to add additional wicks. Drill four holes in the top of the water reservoir and insert two wicks, poking one end through each hole so the wicks form a "U" shape with the ends extended into the growing medium and the underside sitting in the water reservoir. Fill the reservoir with water, and then let the wicks go to work.

Wicking fabric can make effective irrigation setups for seedlings and plant starts. You’ll need a capillary mat or fabric. Lay it flat under your pots with the ends of the mat in a water reservoir. The water will climb up the mat and move under the pots, keeping the soil moist.

Capillary mats are used often in commercial greenhouses, because they’re almost foolproof, and they distribute water evenly and efficiently. Generally, once established on the mat, a pot shouldn't be moved while in production, as it may be hard to relink the mat to the container soil mix. Greenhouses use auto controls to keep their mats consistently moist, but if you have a good reservoir and pay attention to when it needs refilling, the setup should work well at home.

You can make your own capillary mat using a polyester blanket, or you can buy mats at garden stores or online. There are many types of capillary mats available. Some come in kits that include everything you’ll need to get started, such as a reservoir, mat, seedling cups, and adjustable vent covers. Just like wicks, you’ll need to test a capillary mat before sticking it under your pots to make sure it wets well. Once you see how well capillary mats work, you’ll likely want to use them time and again.

David Bainbridge began research and consultation in desert and dryland restoration in 1981. He's the author of A Guide for Desert and Dryland Restoration and Gardening with Less Water, as well as more than 300 papers and reports.