One way of reducing the watering needs of houseplants and seedlings is to grow them on a capillary mat, also called a watering mat. You can find this kind of matting in better garden centers as well as in hydroponics stores. Or just use a piece of old acrylic or polyester carpet.
The idea is to cut the capillary mat to fit the bottom of the saucer or tray. From then on, when you water, moisten the carpet too. That way as the potting mix starts to dry, water will rise from the mat by capillary action, keeping it moist longer. And capillary matting also helps prevent overwatering, as the same mat will also draw excess moisture from the soil of the pot above.
If one layer of capillary mat is useful, you can make it even more efficient by using 2 or 3 layers of fabric. This will allow for less frequent watering.
Better yet, place a piece of plastic egg crating, cut to size, on a few supports and install the mat on top that its ends dip down into the bottom of the tray. You can then fill the tray – which has become a water reservoir – with water and moisture will rise up through the mat to your plants, ensuring up to 3 or even 4 weeks of watering autonomy, depending on your conditions.
Not in a do-it-yourself mode? You can easily find kits that include capillary matting and a water reservoir in hydroponics stores and on the Internet.
If you’re new to indoor gardening using capillary matting, here are two helpful hints.
First, plants will readily root into capillary matting, making them difficult to move. Just giving each pot a quarter turn every week or so will keep wandering roots under control.
Also, capillary mats become dirty over time and algae may even start to grow on them. You can easily fix this by washing your mat in the washing machine using laundry detergent and a bit of bleach. You can use capillary mats over and over if you wash them every few months.
Note that capillary mats only work well on houseplants that like their growing mix a relatively moist at all times. That actually includes most foliage and flowering plants (African violets, philodendrons, ferns, etc.). Young seedlings too grow very well on a capillary mat. However, cacti, succulents and other plants that like their soil to dry out a bit between waterings are not good candidates for this technique.
Also, capillary action will not work if there is a “drainage layer” of pot shards or gravel at the bottom of the pot, as the layer of open substrate will prevent capillary action (water moving upwards from the tray). Of course, using a drainage layer is not considered good horticulture (see No Need for a Drainage Layer) at any rate, but not all gardeners are aware of that. If you do use a drainage layer, you’ll have to repot your plants using the same potting mix from the bottom to the top of the pot before you place them on a capillary mat.