Tips for Planting Successful Containers

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Early last week, we had a freeze warning. I was glad I waited to pot the annuals I purchased the previous week; dragging flats of plants outside the garage during the day, and back inside at night is a whole lot easier than hauling planted pots and flower boxes inside and out.

By mid-week though, I decided to risk it – it’s near the end of May; surely the temperatures shouldn’t drop into the thirties this late, right? (I’m keeping my fingers crossed.) I use containers of all sorts around my yard – their versatility finds their way into almost all my gardens.

Most flowering shrubs and perennials provide their colorful display for only a few short weeks. Annuals provide non-stop color all season long.

Potted plants can brighten a shady area.

Or be used to provide interest in an empty spot in a garden.

Herbs, vegetables, annuals, perennials, shrubs, small trees – or a combination thereof, can be planted in any type of container as long as it provides adequate drainage. Special care needs to be taken to over-winter potted perennials, shrubs, and trees – but that’s a topic for another blog. It’s not even summer yet; who wants to think about preparing for winter now?

Whatever plants you choose for your containers, it’s important to get off to a good start – it begins with the soil. There are many types of potting mixes available. The advantages to using a soil-less mixture is they have everything included – vermiculite or perlite, moisture-retaining granules, and fertilizer. They are light weight; a plus for hanging plants and window boxes, or if you’re moving pots around the yard to take advantage of the sun. The disadvantages are they can be expensive, and they’re too light; they tend to turn into a cardboard-like consistency mid-way through the season. Topsoil or compost is too dense for container gardening. Heavy-feeding annuals and vegetables need a soil that will stand-up all season; perennials, shrubs and trees, for multiple seasons, but one that will also not compact so much that water can not drain from the container.

The solution? Bulk up the potting mix with compost, peat, manure, or topsoil. I use a half-and-half mixture of a good basic potting soil and what we call “barn-dirt” at the nursery – the pH balanced mixture of topsoil, bark mulch, and compost that is used to pot everything from trees to seedlings. Inquire at your local nursery if the soil mix they use is available for sale; it’ll be richer and stand up longer than anything you can buy in a bag. Though a good base, it’ll still be a bit heavy for annuals, and can also be a bit on the expensive side.

A wheelbarrow is the perfect vehicle to start your soil mixture. It can be carted to your containers, rather than hauling heavy, filled pots to their final resting place in your yard. Once I’ve got my barn-dirt and potting soil in the wheelbarrow, I’m still not quite ready to plant yet. Because nutrients leach and moisture evaporates more quickly from containers than from the ground, adding a good slow-release fertilizer and a moisture-retaining polymer ensures healthy plants that don’t wilt quickly in the blazing sun. The moisture-retaining polymer is wonderful stuff for those of us whose watering practices aren’t as consistent as they should be. These polymers are little crystals that swell with watering, and hold moisture in the soil. It’s important to follow the recommended rates of application according to pot size. Don’t use more of this product than recommended on the package – it can swell so much it can actually push your plants out of the soil. It might sound like a lot of work just to get started, but your plants will thankful you went to a little extra trouble.

But what if you have soil left from last year still in your containers? A common question I get at the nursery is, “Can I replant my pots using last year’s soil?” The answer is both yes and no. The old soil is basically considered “dead”; most of the nutrients have already leached from it. It can be used though on the bottom of a deep pot as filler – keep approximately ¼ of the old soil on the bottom, and add ¾ new soil to plant in. Annuals don’t have deep roots, so when using a large pot, I make use of the plastic containers the plants came in – overturned on the bottom of a pot, they save me having to fill the entire container with soil.

Once ¾ of the container is filled with soil, start placing your plants. Begin at the center and work your way out, filling in soil firmly around each plant as you go.

Plan your containers based on the amount of sunlight they will receive; mixing shade plants and sun-loving plants in the same pot will sentence one or the other to failure.

Keep your plants in portion to the container. Three or four little marigolds in a big pot look forlorn and lonely; the number and size of the plants are disproportionate to the pot. Don’t be afraid to pack them in – these two pots of begonias contain at least twenty to twenty-five plants each, (I lost count). Full now, they’ll be even more lush and beautiful as the season progresses.

With those simple things in mind, anything else goes. Experiment with wild color combinations, different textures, a mix of annuals and perennials, herbs and vegetables. Be creative. Have fun. And don’t forget to water!