Probably the most frequently asked question I get asked when people find out about my interest in plants relates to the watering of houseplants. Specifically, people want to know what I call "the houseplant numbers"-meaning they want to know how many cups of water they should give their houseplants per week. Unfortunately houseplants don't operate on our schedules and they don't understand liquid measurements.
There are various factors that come in when watering houseplants like the lighting condition, quality of the soil and what kind of pot you choose for your houseplant. Some people will insert their fingers into the soil in an effort to gauge the moisture in the pot. Seems like it should work but what if your houseplant is in a large pot or in a very small pot? Sticking my finger into the first two inches of soil doesn't tell me much about the moisture of the soil eight inches below the tip of my finger. Some of the houseplants I grow are in pots two inches small, where do I put my finger then?
Manufacturers of gardening ephemera came to the rescue a while back and offered us moisture meters for houseplants. You insert a probe into the soil and it tells you how dry or wet the soil is below. The problem I have with moisture meters is that I find them unnecessary and not very reliable. When I first started growing houseplants I bought one and still over/under-watered my houseplants to the point that I killed many. Eventually the moisture meter broke and when I looked at the packaging to find a number to call and complain I found a warning that read; "Do not expose probe to liquids." Think about that for a second.
The trick to watering houseplants I learned while working in a bonsai nursery years ago. One day I was checking on some plants and inserting my finger into the pots to see if they needed watering when the owner told me to pick up the pot. "Is it heavy or light?"he asked as he walked out the room before I could even answer. Two days later he stopped me near the same plant and asked me to pick it up again. A little confused I picked it up again and he asked "Is it heavier or lighter than the last time?" Worried I would answer wrong I hesitantly replied "It feels lighter." "That's because it needs watering now" was all he said. The exchange was exactly like something out of The Karate Kid movies except I wasn't learning karate and the guy teaching me the lesson wasn't Asian... but... other than that it was exactly like a lesson from the movie.
Ever since then I have been picking up my houseplants and feeling how heavy or light they are. The next time you water your houseplant pick it up and feel the weight of the plant, pot and saturated soil combined. Then pick up your plant again before the next watering and observe the difference in weight. Repeat this for a couple of waterings and you'll soon be able to tell when your plant needs watering simply by picking up the pot. I've gotten so good at this that I can water in the dark without turning on the lights and the best part is that I don't have to get my fingers dirty and I don't have to keep buying moisture meters.