Get Growing: Tips for containers that last

Do you, like me have some windowboxes that need refreshing? 

With the rising cost of plants, it can be pricey and time-consuming to replant main containers every few months. First you find and purchase new plants – which, for me is fun, but it may not be for everyone. This also includes picking a color scheme, but more on that later. Then it’s time to remove any sad, withered former plants to the compost, and topdress with either new potting mix or compost to give the old soil a little boost of nutrients. That plus the cleanup could take several hours every few months. 

Most people think of annuals for long-lasting container color – and it’s true, they will keep their flowers longer than other plants. However, they also need to be replaced when the weather stops suiting them.

So what’s the answer? Read on.

I had the pleasure of working for several years with a container master, Ravenna Gardens designer Barbara Libner and gleaned a fraction of her techniques, if not her artistry. To learn much more, check out her online course in container design with Fine Gardening magazine (finegardening.com). 

One thing Libner does to create four-season interest with less hard work is focus on perennials and evergreen foliage over short-lived annuals.  She will often start with a centerpiece or backdrop that is an evergreen or persistent plant with winter interest. Depending on the size and location of the design, some examples might be a small upright Euonymous, a dwarf conifer, a Japanese maple, a lavender, rosemary, or evergreen sedge (Carex).

Supporting cast members can include other perennials that keep their leaves all winter, like Heuchera (coral bells), sedges, creeping sedums, or a prostrate rosemary.  Seek out ones with beautiful or unusual foliage, which lasts much longer than flowers. 

For eye-popping design look for elements that match and contrast. Pick a narrow color palette, ideally two colors and stick with it. Use leaf veins and stems as well as flowers to create color echoes, like a calibrachoa with gold foliage and a lemon eye can be paired with a chartreuse carex. Add spice with some strong contrasts too – if your palette is reds, add sultry burgundy or black foliage to create depth.

Try to contrast shape of blooms, plant habit, and foliage. A white ranunculus looks a bit too much like a geranium to be neighbors – they’re both globes. But spiky grape hyacinth looks great with ranunculus. 

Yes, you can still do the popular “thriller-spiller-filler” formula – which translates to a vertical or splashy accent, a trailing plant on the edge, and filler for the middle ground.

Cram the plants much tighter together than you’re used to doing in flower beds. They won’t mind. Once you’ve got your palette of nicely contrasting long-lasting foliage, you can add the sparkle – one or two annuals in your chosen palette. In early spring (and fall), the first available will be pansies and violas, followed by geraniums, petunias and calibrachoas, then snapdragons and a host of specialty annuals in early summer. These are mainly plants thriving in full or partial sun — 4-6 hours of direct sun.

If you’ve got a shady container, your best bets for annuals are pansies and violas, then begonias and/or fuschias. For the coolest foliage, look to perennial hostas and heucheras, or annual caladium and coleus. You can find nearly every color in the rainbow among these – and the color lasts for months. In winter, consider annual ornamental kale in a trippy purple or warm white. 

Most fuchsias for sale are annuals for hanging baskets, but did you know there are perennial and nearly perennial fuschias? The true perennials tend to be large shrubs, but a favorite upright fuchsia for containers in partial shade is Fuchsia ‘Gartenmeister Bonstedt’ which has amazing dark gray-green foliage with bronzy veins and coral flowers. This one can bloom for months, and with protection (indoors or possibly wrapped), has a chance of making it through the winter in Seattle.  

One container winner that has amazed me is a tiny native Gilia capitata, growing in a windowbox style planter near my front door. It doesn’t get more than 5” tall even in bloom, but its basal rosette stays evergreen through the winter. It creates little buttons perhaps a ¼” wide in the richest blue-purple starting in March. I should probably fill the whole box with them – or perhaps with a line of gold carex in the back, for the contrast. 

If you enjoy starting plants from seed and don’t mind some gaps in your containers occasionally, you could use half-hardy annuals to provide some flower power. With deadheading, calendula flower a long time in spring, often repeating the performance when weather cools down again in September. Another choice are fast-growing annuals like alyssum, which makes a frothy, fragrant edging or skirt for other plants. I am winter-sowing some now in recycled containers outdoors for that very purpose.

I like to add slow-release organic fertilizer at planting, and if they need some help mid-season, supplement with liquid organic fertilizer whose nutrients are available to the plants instantly. Containers need much more water than their in-ground counterparts, and if you are growing perennials and mini-shrubs as we just discussed, they’ll need regular watering for at least two years to become established. In hot summer weather that can mean daily. Mulching or growing groundcovers can help preserve moisture in your pots.

There are as many strategies for containers as color preferences, but these will get you started to a fuss-free relationship with your windowboxes and entry containers.