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Tricks of successful container gardening

TIP: Don’t put gravel on the bottom of containers, says Jennifer Brennan. It can interfere with water flow. Water can pool among the roots — and kill the plants.
TIP: Don’t put gravel on the bottom of containers, says Jennifer Brennan. It can interfere with water flow. Water can pool among the roots — and kill the plants. Chicago Tribune

Trends come and go in gardening. Remember when you couldn’t run through a neighbor’s flower bed without tripping over a gazing ball? But for decades now, container gardens have been a mainstay in the landscape. And with advances in technology, it’s getting easier to keep your containers looking spiffy.

“Container gardening is one of the areas of the gardening world that never seems to die,” says Jennifer Brennan, a horticulture information specialist at Chalet Nursery in Wilmette, Illinois. “We always thought it’d die out, but as people are downsizing and leaving big gardens behind, they don’t want to give up gardening altogether. And (for) millennials, container gardening fits their lifestyle, an urban lifestyle. They put them on their balconies.”

It’s people such as Brennan who bring new concepts to gardeners, and that helps keep containers on balconies, porches and patios year after year.

Here’s her advice:

▪ Busting a drainage myth: Many gardeners believe that putting several inches of gravel or rocks in the bottom of a pot will facilitate drainage. But, Brennan says, it’s detrimental to the plant. Blame Thalassa Cruso, a plant expert who was often a guest on The Tonight Show when Johnny Carson was the host.

“She was this older British woman, and she’d boss Johnny around in the ‘70s,” Brennan says. “She’d talk about houseplants and potted plants. It was ‘Teach Johnny how to do it,’ and he’d always mess up. But she would say, ‘You have to have three inches of gravel in the bottom.’”

Such a setup, Brennan says, forces the water to reorient itself before it can flow smoothly down and out of the pot’s drainage holes. Research has shown that if there’s just one material, the flow is better and the water is less likely to pool among the roots before it can realign itself to continue its downward flow.

“Any time roots sit in water more than 20 minutes, it can kill them,” Brennan says. “And if you also take away three or four inches of root capacity (for gravel), that’s significant.”

▪ Fertilizer upgrade: The development of time-release fertilizers was a huge step forward from the water-soluble fertilizers many gardeners still use, and which still are sold in garden centers and even grocery stores.

“They’re advertised, like, if you use them once you’re going to win (at) the state fair,” Brennan says. “They will work for a week. But time-release fertilizers are remarkable. They’re meant to last four, six months. The nutrients are there when the plant needs them.”

▪ Acrylic polymers: Polymers hold 200 times their weight in water, which is released gradually, allowing you to water a lot less frequently and reducing the attention one must pay to containers in dry weather, she says. One product she recommends is Soil Moist, available at most garden centers and online.

▪ Planting savvy: Here’s how Brennan suggests planting a container: Instead of filling the pot with dirt and then digging a hole to drop a plant into, fill the container to within 4 1/2 inches of the top. Remove the plants from their 4-inch containers and set them in place. Next, add the acrylic polymer and time-release fertilizer, then fill in between the plants with potting medium. Remember, roots grow down and out, not up, so don’t bury the plants in your potting medium. Rather, keep it level with the top of the root ball.

▪ All in the numbers: How many plants per container? A general guideline: Take the diameter of the pot and divide by 2 to get the number of plants. So, a container that’s 12 inches across would accommodate six plants.

▪ Potting medium: At Chalet, they use a soilless mix. “When you get soil, it has living organisms in it,” Brennan says. “That’s great in the yard. But in containers there will be too many pathogens and insects. Also, (a soilless mix) is more pliable.”

She says the public has become accustomed to the term “potting soil,” so that’s the label that commercial companies use. “But it’s not soil,” she says. “It’s potting medium.”

The mix that Chalet uses consists of shredded/compacted root bark, long-fiber sphagnum moss, short-fiber moss (peat) and perlite.

“The secret is the roots can grow very quickly (with that potting medium) and get established,” she says. “And when the roots are established, the tops can grow.”

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