The Iowa Gardener: Make sure your annual container plantings stay show worthy till fall

I visited my sister in Amish-country in Pennsylvania in August and her containers were jaw-dropping. They were full, lush, disease-free and blooming like the cover of a garden magazine: Cascading petunias, lush sweet potato vine, luxurious coleus, and soaring annual salvia, among others.

How did she do it? Her answer was simple, but not so simple to stick to: Lots of water and lots of fertilizer.

I thought I was doing that back home in Iowa, but when I saw hers, I realized I wasn't. If you're taking great care of annual containers, they will be at their peak in July through September. Mine, instead, were looking sad and tired, as if they couldn’t wait for a merciful death with the first frost.

So here's how to have containers so spectacular they'll make your sister want to write a garden column about them.

Provide the right amount of sun

My sister's containers are all in full sun — eight or more hours of unfiltered sunlight a day. Appropriately, they are planted with annuals that require full sun. If she had any less, their growth would be stunted.

If you want to put your container in shade (only four or so hours of sun a day) or part shade (less than four hours of sun a day), choose plants at the garden center that specify that.

This can be a little tricky. I got some wonderful angel wing begonias for my back screened porch, but I had to move them to deeper shade under a tree in the backyard because their leaves were getting sun scorched. Sometimes it takes trial and error to figure out how much sun or shade you have in different parts of your landscape.

Make sure you have excellent drainage

Never plant outdoors in containers that don't have excellent drainage or your plants will drown during rainy weather or just be soggy and struggle. I bought two large fiberglass outdoor pots this year, each with one small punch hole at the bottom. I punched the hole, but the soil has been overly moist and the plants in it struggled. This fall, when I empty the pots, I'll drill more and larger holes. And never plant in a pot that has no drainage.

Water, water, water

Like other gardeners with gorgeous containers, my sister says that unless she gets a heavy rain (not just a light rain), she waters her containers every single day. (In case you missed that, that's Every. Single. Day.) And sometimes twice a day when temps are in the mid-80s and above.

I plead guilty to letting my plants get a little wilty before I water. The goal is to water them before they wilt. Wiggle your finger in the soil to see if it's moist. Or look at the leaves. Often they'll get less shiny if they are getting on the dry side. Letting them get too dry stunts their growth and dramatically cuts back on flower production.

  Buy Photo

Feed, feed, feed

The most successful containers are fertilized in two ways.

The first is with slow-release fertilizer, which is usually granular, that is worked into the soil at planting time and releases nutrients over the next several weeks. This provides a baseline of nutrients. Some potting soils have slow-release fertilizer added to them. But slow-release fertilizer peters out after a few to several weeks, depending on the formulation. By at least, midsummer you need to reapply the slow-release fertilizer.

To supplement slow-release fertilizer, you need to provide a second type of fertilizer as well: Liquid fertilizer, which provides quickly absorbed "snacks" of nutrients. Apply liquid fertilizer every week or two, depending on package instructions.

For flowering containers, it's important to choose a fertilizer made specifically to enhance blooming. Other types may encourage green leafy growth at the cost of blooms.

Many liquid fertilizers are sold as powders that you dissolve in a watering can and then pour into the container for one-step watering and feeding.

Whatever fertilizer you choose, it's important to measure and follow the instructions. Putting on too much liquid fertilizer can actually burn your plants.

Containers are designed to look at up close and personal, so regular grooming is important. Pinch or trim off spent blooms regularly to encourage more flowering. If leaves or stems become damaged or diseased, trim them out. And if anything gets leggy, don't hesitate to trim it off or pinch it back to keep growth compact and full.

  Buy Photo

Veronica Lorson Fowler is co-publisher of the Iowa Gardener website at www.theiowagardener.com.