By Larry Hodgson
I like to get my container gardens started a few weeks ahead of time. On one of those rainy days when I can’t get outdoors, I pull out a few containers, fill them with soil and start picking planting material from among my trays of seedlings and cuttings. Or head off to the local garden center to fill up on greenery. Back home, I just sort of throw the plants together, water a bit and stick them in front of a sunny window until the time comes to put them outdoors. What a pleasant way to spend an otherwise dreary day!
If you’ve never tried preparing your own containers, here are a few tips for preparing successful mixed plantings for your balcony or deck.
Pots: the Key to Success
Start by finding a suitable container… and that means a big pot.
Beginners often come home from the nursery with an itsy bitsy flowerbox, then struggle all summer trying to keep it watered. It seems odd to say this, but a plant’s soil is its main water reservoir. If doesn’t have much soil, it will dry out in no time. When you need to water a pot twice a day just to keep the plants alive, you’re not going to get great results. So up the pot size… and maintenance will drop accordly. In a big enough pot, watering once a week is probably all you’ll need!
You can theoretically get by with a flower box 8 inches (20 cm) high and deep, but I try for 1 foot (30 cm) high and deep. That’s quite a bit larger than the standard size, but so much easier to maintain.
As for pots, that’s much easier: there are lots of big, deep pots to choose from. Designers seem to be going wild with pot design these days, so have fun shopping! If you’re afraid yours will be too big to move around, put it on wheels. Yep, you can find plant dollies that make zipping plants around a snap.
Some pots come with a “water reservoir”… which you totally don’t need. Again, the pot’s soil will be the main water reservoir. An added water reservoir isn’t harmful, it’s just that it isn’t really useful. Not outdoors anyway.
Hanging baskets? The bigger the better. Nothing dries out faster than a small hanging basket!
Any container you use has to have one or more drainage holes (unless you’re planning a container water garden, that is). If there is no drainage hole, drill a few.
Pot color can be a factor! Black or very dark pots can overheat if you place them in full sun and this can harm plants. You can cool dark pots off by wrapping them in burlap or by placing them inside a paler planter. If you’ll be gardening in the shade, though, or if your summers are cool, pot color is of little importance.
You’ll need to buy some potting mix. Any light blend will do: it doesn’t have to say “container mix” on the label. I buy bales of houseplant mix and use it for everything. You can add compost for better tilth: up to one part compost for two parts potting mix. Don’t use garden soil: it is too dense and compact and likely contains pests and diseases.
What about last year’s potting mix? Most merchants suggest replacing your mix annually… but they have a bigger gardening budget than you do! I just keep using my original potting mix over and over again, simply topping it up with compost or fresh potting soil (the original soil compacts downwards over time as its ingredients decompose). If you find that your old mix is really too dense (often the case after 4 or 5 years), add vermiculite or perlite to fluff it up again.
This is the fun part! Raid your garden center and fill up your car to overflowing with incredible plants. I don’t even calculate what I really need: I can always find and recycle some old container as a new planter if I’ve bought too many.
You can pot up plants individually if you want and then group them together to create the design of your dreams. I do this with plants I’ll later be bringing indoors as houseplants: it saves me having to dig them up and repot them in the fall.
As for more traditional annuals, I figure most belong in mixed plantings. You can grow almost any combination of plants in containers: annuals, herbs, vegetables, tropical plants… even perennials and shrubs! However, ideally you should choose plants that will be attractive all summer. Annuals, with their constant bloom, are the most popular plants for ornamental containers, but remember that plants with attractive foliage, even if they don’t have flowers, also create great effects when blended together.
In mixed plantings, the most important thing to remember is that all the plants in the same container must have similar needs. If you try to grow a plant that prefers shade and moist soil with a plant that likes full sun and dry conditions, one or the other will have a hard time of it! Fortunately, most flowering plants prefer a sunny to partially sunny location in soil kept relatively moist, which makes choosing a lot easier.
Thrillers, Spillers and Fillers
You’ve probably all heard about the “thriller, spiller, filler” trio (I’d love to know who originally coined that: if you know, I’m all ears!)… and guess what? It works! The idea is to use, in each container, one thriller – a taller, more dominant plant – either in the center or towards the back, then add a few spillers (trailing plants) to soften the edges of the container and partly cover its sides.
See all that empty soil in between? That’s where you drop in the fillers: more modest-sized annuals with a shorter, bushy habit. Their role will be to ensure that the pot still seems full to overflowing (the human eye just loves exuberance!).
Among thrillers, consider cordyline or spike dracaena (Cordyline australis), purple fountain grass (Pennisetum × advena ‘Rubrum’), cannas (Canna spp.), fuchsias (Fuchsia spp.) or any of the taller annuals (I like to use some of the taller coleus as thrillers, notably because they do so well in shade and I don’t have room in sun for all my containers).
Spillers are usually quite obvious, even in the nursery, with their naturally drooping habit. Think of some of the more spreading types of calibrachoa (Calibrachoa spp.) and petunia (Petunia × atkinsiana), bacopa (Sutera cordata), licorice plant (Helichrysum petiolare), ornamental sweet potato (Ipomoea batatas), vinca (Vinca major), indoor asparagus (Asparagus densiflorus), and just about any plant bearing the name ivy (Hedera, Plectranthus, Senecio, Glechoma, etc.) Or, take a few cuttings from your yard’s groundcovers, such as yellow archangel (Lamium galeobdolon) or golden moneywort (Lysimachia nummularia ‘Aurea’).
Finally, the list of “fillers” is enormously long, too long to repeat here: there are literally hundreds of varieties that would do. This includes most of the traditional annuals such as petunias (Petunia × atkinsiana), marigolds (Tagetes patula), begonias (Begonia × sempervirens-cultorum), pelargoniums (Pelargonium × hortorum), shorter coleus (Plectranthus scutellarioides), etc. Just take your pick!
Start by covering the pot’s drainage holes with a piece of screen, an old nylon or sock, a used coffee filter, or a piece of newspaper. This is to prevent the soil from washing out onto your deck or table when you water. Despite popular belief, there is absolutely no need to add a “drainage layer” of pot shards or gravel to the bottom of the pot.
Now fill the container about three-quarters high with potting soil. Mix a slow-release organic fertilizer into the mix at the dose recommended on the product label. It is not necessary to limit yourself to “container fertilizers”: any fertilizer will do. Now water before planting, mixing with a trowel until the soil is evenly moist.
Unpot the plants and place them here and there to see the effect. When you are satisfied with their look, simply add more soil around the plants, covering their root ball up completely, but without burying the collar (where the stem meets the roots) more than superficially.
All that’s left to do is to water well.
If you’ve been growing your container indoors, start acclimatizing it to outdoor conditions when the weather warms up, even if that means bringing it indoors or into a garage or tool shed on excessively cold nights (below 50˚C/10˚C). Put it in the shade at first, then, after 3 or 4 days, in partial shade, then in sun… at least, if that is where it is to spend the summer.
Finally, set your pots out in their permanent home (balcony, deck, terrace, roof, etc.) for the summer. Of course, they are container gardens: if you want or need to move them around, feel free to do so.
During the rest of the summer, just water as needed, that is, when the soil is dry to the touch, adding a soluble fertilizer, such as liquid seaweed, once a week. Prune out any wayward stems if they bother you and spin the pot around occasionally if you find it leaning towards the sun (this will happen in part shade and shade).
Note that most modern annuals no longer need deadheading: they’ll keep on blooming all summer if even you don’t pinch out the faded blooms (a great step forward, in my opinion!).
And that’s about all.
Even with what appears to be truly minimal maintenance, your container gardens should remain beautiful all summer!
Article derived from one appearing in this blog on April 24, 2016.
Ill.: Claire Tourigny