Beware, Watering Can Be Deadly

It wasn’t my fault, I didn’t kill it. Really. It’s just too darn easy to kill potted plants in summer with either too much or too little attention.

In the case of the shriveled terra cotta-colored million bells, it was too much water, which looks exactly like too little water. You can only tell the difference by picking up the pot, which will feel heavy if the soil is too wet, and weigh next to nothing if too dry.

That is the best way to judge if a plant needs water or not. In summer and in fall, the surface of the potting soil is going to dry almost immediately and if you respond to this visual clue by watering, you might be overdoing it since the soil just below the surface could be soaking wet. The finger-in-the-soil testing technique may be necessary if the pot is too big to easily pick up. It is certainly better than not physically checking at all. Never rely on how the soil looks.

Keep the soil too wet and it will rot the roots right off the plant. With no roots, the plant appears to be wilting from lack of water, but it was actually too much water that caused the roots to rot in the first place. Watering at this point only hastens the plant’s demise. No wonder over- and under-watering are often confused: They have the same symptoms.

Ideally, you shouldn’t have to water container plants daily. A pot should store water for several days, and plants are often happier if the soil begins to dry. As soil dries, air is pulled in and air is as necessary to roots as it is to leaves.

Putting a layer of gravel or broken pieces of pot in the bottom of containers doesn’t help drainage or the health of the plant, but you can forestall clogging by using nylon window screening over the drainage holes. The screening keeps out slugs and bugs while keeping soil in the pot, but water passes easily though.

A good potting mix contains organic matter such as ground bark or peat moss that stores water. Inorganic components such as sand or perlite are mostly particle separators so air can get into the mix. There are polymers in a few mixes that act like little sponges and store extra water, or they can be added to mixes.

I blame the death of my little million bells on lousy potting soil. Years ago, a researcher with the University of California tested commercially available potting mixes and found that many, if not most of them, performed poorly. The brands have changed since then, but I think many of today’s mixes are even worse. They wear out way too fast and often drain poorly from the start. If you keep having problems with plants in pots, consider looking for a better potting soil.

I have never found an inexpensive mix that works well, though one I tried years ago was quite amusing. It had colorful shreds of telephone wire in it, which made the soil look like the day after New Year’s. Presumably the bits of wire were in the mix to speed drainage.

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Most inexpensive mixes I’ve tried need to be replaced almost every year and some of them get so soggy they are useless for anything but bog gardens. And straight garden clay works better as a potting soil for bog.

I’ve been on a quest for good potting soil for several years. I’ve found three premium brands that have admirable qualities. They hold just the right amount of water and nutrients and they last for several years in a pot.

I’ve had good luck with Uncle Malcolm’s, KLM brand and Nurseryman’s. These are what potting soils ought to be. (They are not the brand that killed my little plant!)

You can even use these for starting seeds, but first run the soil though a screen with 1/4-inch openings. Nurseries sometimes sell these potting screens, or “riddles,” or make your own. They take out the chunkier pieces that improve drainage but interfere with germination.

Eventually, after a year or two, potting soils just wear out and become too compacted. Even the best potting soil will not last forever. Drainage slows and the soil becomes airless, which encourages root diseases and rotting.

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It’s time to repot when water doesn’t quickly drain. You can trim back the roots and the top of a plant and repot it into the same container--with some fresh potting soil--or simply move it up to a larger size.

Make sure to put a screen over the drainage hole, do not fill the pot too full (leave room to water), and do not bury the plant below the new soil level (which can cause crown rot).

You have the same choices when a plant becomes root bound or too big for its pot. Un-pot it and trim back the roots and some of the top or move it to a large container.

When repotting in summer, keep plants in partial shade until they become accustomed to their new quarters (a week or two). You can also move plants into partial shade on really hot days or while on vacation.

Old potting soil can be revitalized by adding quality peat moss or soil amendment, but it will never be quite as good. Use it on less fussy plants, or simply use it in the garden as a soil amendment or mulch.

Plants confined in pots need fertilizer because potting soil is artificial and has no natural nutrients. You must add the nutrients or plants go hungry, which is not necessarily a bad thing. Plants bloom and fruit better when they are a little hungry.

You may want to fertilize annual flowers and vegetables on a regular basis, but don’t fertilize too often if you don’t want plants to outgrow their pots.

Pelletized slow-release fertilizers (such as Osmocote, Sta-Green and others) are the easiest way to feed, or use liquid fertilizers in a watering can once a month or even less. Mild liquid fish is hard to beat, but it smells awful. Chemical fertilizers (such as Spoonit, Peter’s, Miracle Gro) are stronger and should be diluted by about half if you don’t want crazed growth.

When watering, use some kind of diffusing device on the end of the hose, so you do not wash that valuable potting soil out of the pot. It will also keep the water from churning the soil, thereby destroying its porous structure.

A wand makes it easier to reach plants, and an on/off valve saves water between pots.

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Write to Robert Smaus, SoCal Living, Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012; fax to (213) 237-4712; or e-mail robert.smaus@latimes.com.