We all know that indoor potted plants need water to survive, but do we really know how much or how little? And while we may have developed a schedule over time, it turns out that watering plants is a bit more complicated than periodically wetting the soil. Yes, your plants will survive, but with a few simple techniques, they can really thrive.
Potting soil is NOT soil
The first order of business is to understand that potting soil is not soil per se, but a soil-less mix composed of different quantities and sizes of organic and inorganic ingredients. Organic components may include sphagnum moss, aged bark, compost, sawdust and/or coir (the fiber outside of a coconut shell.) Inorganic components may include sand, perlite, vermiculite, rockwool (a product made from basalt and spun into fibers) and occasionally polystyrene beads. Sphagnum peat moss is the most commonly used ingredient in potting soil and usually accounts for 50 to 75 percent of the mix.
In potting soils, porosity is vital, allowing water and air to travel through containers so that your houseplants can flourish. The different organic and inorganic particles make up the particular structure and texture of each mix while binding together in various ways to give potting soil its ‘fluffy’ quality. As water passes through the pot, it travels through the pores in the potting soil, attaching itself onto some particles (that hold on to the moisture) and flowing past others.
This makes good sense when you consider what your indoor plants may need to survive while housed in those plastic, clay or ceramic pots. Unlike outdoor plants that can continuously nourish themselves in the ground from nutrient-rich soil, indoor plants are confined to their own little container. It’s up to you to control their world.
And, don’t be fooled that your indoor plants would prefer to live in soil. Never add garden soil to your soil-less mix, it will reduce particle size and choke your plants. Garden soil is too heavy and compacted and its pore spaces are too small. It will reduce your houseplants’ ability to absorb water and air that is essential to their wellbeing.
Contrary to popular belief, pushing or pressing down on the potting mix is not helping your houseplant. Soil-less mix is all about aeration and porosity to allow water to reach the roots and oxygen to infiltrate the soil. If you compress the ‘soil,’ you are cutting off a vital air source to your plants’ roots. Instead make sure the potting mix stays fluffy and light to ensure the best conditions in your pot.
Watering to remove salt build-up
By now, most of us know that plants should be watered deeply and less often. But, how many times have you watered your plant thoroughly only to find it dried out the next morning? The answer lies in the structure and texture of your particular potting mix and how long it takes for the different particles to absorb water.
You may have noticed occasionally a build-up of what looks like salt on the ‘soil’ surface. As potting mix decomposes, it creates more minerals, especially salt, that over time cause the plant to decline. The water you’re using can contribute to this problem, too. While your houseplant may have started out in the greenhouse with a healthy mix of minerals, over time, salt build-up can spell disaster for plant health. Much like when we eat more food than we need.
To prevent this problem, you need to flush your plants regularly with water to help wash the salts and additional minerals away. Happily, this is also the most effective way to water. Place your plants in the sink and irrigate them slowly for up to a minute (gradually, not full-on from the spigot.) This will enable the salts and other accumulated minerals to wash through the soil and on out through the drainage holes.
Watering to sustain moisture
Leave the pots in the sink for an hour so that they drain completely. It may seem like over-kill, but this will enable the particles in the potting mix to thoroughly absorb the water and hold on to it for days. Never place your pots immediately back on the saucer. Tender roots hate to be stuck in water and they’ll rot, causing the plant to eventually die. Be patient, it’s worth it.
Replace your pots on the saucer and enjoy knowing that you have restored your plants to optimum conditions for good health and longevity. Allow the top few inches of the soil to dry out before watering again.
A word on fertilizing, with all the salts and minerals building up in the pot, there’s little reason to fertilize as often as you’re probably doing. Fertilizing at a 1/4 to 1/2 strength every other week during the growing season is sufficient to keep your plants healthy and looking their best.