How not to kill your Houseplants, Part I: Watering
Overwatering (or underwatering) is by far the most common killer of houseplants, but also one of the easiest to recover from. How many times have you brought home a little gem before finding it slumped over only a few days later, browning at the edges? Believe it or not, there is definitely such thing as too much water, and you’re probably doing it.
Not too wet, not too dry
Plants need a mixture of both water and air to maintain a healthy root system. Sitting stagnant in water for too long will actually suffocate a plant’s root system, and create the perfect conditions for rot. That means that in order to stay alive, most plants need the soil to be dry enough in between watering that air can seep down into it.
While it’s good to set a schedule to remember to water, it doesn’t mean that you should always water plants once or twice a week. Depending on the type of plant and the amount of light, heat, and humidity in a room, plants have very different watering needs from season to season and room to room – some (like my bonsai trees) need water almost every day, while others farther from a light source get water only every few weeks.
While every plant is different (look up your plant’s species online if you’re concerned), the general rule of thumb is that your potting soil should feel dry to the touch, and that dryness should extend about an inch down into the pot.
Check if it’s time to water
Poke a wooden chopstick into your pot at about an inch depth. When the chopstick comes out dry, it’s time to water. (You can also use your finger!)
Once you do water, don’t just dump a cup into the pot and leave it alone. Water that runs through your plant and sits stagnant in the cachepot or tray gets sucked back up into the plant, meaning that roots at the bottom of your pot never get a chance to dry out. What’s more, watering a plant is like us drinking water – they drink and absorb what they need, and use any excess water to flush out what they don’t need. If that “flushed” water sticks around, it just means that all the stuff your plant has rejected (chemicals in your drinking water, extra fertilizer in the soil) gets stuck in the soil – sometimes you can even see this chalky, white residue on the soil.
Water the right way
Put your plant in the bathtub or sink and fully saturate it with water – if you can use the gentler, dispersed sprayer so that the soil doesn’t get jolted too much. Let the water fully drain out, and then repeat. (If your soil is particularly contaminated, it’s good to flush it twice: once to get the crap out, the second time to let the plant really drink). Once your plant has drank its fill and drained, put it back in the pot to slowly absorb any water left in the soil before its next drink.
If you’ve been overwatering or letting plants sit in water for too long, it’s possible that you have rotten roots – a problem that plants can’t always recover from without a little human intervention.
To heal your plant’s rotten roots: Once you’ve let the soil dry thoroughly, take the plant out of its pot and comb any excess soil out of the roots with your finger. Do the roots feel spongy or slimy in some areas? Cut away anything that’s obviously rotten with pruning shears (keep at least 50% of the roots intact) and replace your potting soil with new stuff. If there’s a lot of rot, try mixing a handful of activated charcoal into the new soil – it is both a natural purifier and it helps soil dry out more quickly in the future.
Make sure your soil suits your plant.
Just like every type of plant needs a slightly different amount of moisture, every plant needs a slightly different soil mixture. Think about what the plant’s natural environment would be like in the wild – did it evolve to thrive in the desert? Or a swamp or rain forest?
Plants that come from dryer climates (cactuses, succulents, palms) need more air than water – that means using soil that doesn’t absorb water as well. Drop pumice, trap rock, or broken pot shards into the bottom of the pot so that air can seep up easily from the bottom. On top of that, add a layer of smaller gravel, and then finally a mixture of sand and soil that you’ll nestle your plant into. The sand doesn’t absorb any water, so it means that air will always be able to travel through the pot and into the roots, even right after you’ve watered. Keep in mind: sandy, rocky mixtures don’t have as many nutrients as potting soil, so your plant will probably need more fertilizer than other plants.
Plants that naturally grow near water or in rain forests (ferns, orchids) should stay relatively moist. That means keeping the non-absorbent material to a minimum, meaning the soil stays damp much longer. These should still be flushed after watering, but shouldn’t be allowed to get too dry in between. These plants are also particularly sensitive to humidity – make sure that any moisture sucked out of the air by your radiator is replaced: add a humidifier, mist the leaves with water, leave your shower door open or set a big pot of water to boil away.
Going away for a while?
While it helps to have a friend water your plants while you’re on vacation, finding the right person doesn’t always work out. Knowing that plants don’t need as much water in low-light and high humidity, I’ll actually move plants into a dark bathroom for shorter trips, letting them sit in the tub with a bit of water at the bottom after watering. I make sure that the pots are elevated, not soaking - that way they’ll get a little consistent evaporated humidity without soaking all week or weekend.