When you think of container gardening, the first thing most focus on is using only annuals. You know those common plants that are crammed into the containers by the dozens. But what if the common plants were used differently?
Using perennials in containers has become increasingly popular over the years. Many of our annuals are perennials elsewhere in the world. We are just using them with no expectation of them returning next spring.
I never really thought to write about container perennials because I have been doing it for so long, it never dawned on me that it actually was an emerging trend. I even grow tender shrubs in containers and over-winter them indoors (greenhouse is better).
It is so easy when dividing perennials or digging up shrubs to re-use them in containers. Over-wintering tender perennials in containers is not quite as easy in our climate though, but can be done with some useful tips.
1. Use a large fiberglass or metal container, not a large ceramic pot which would crack in winter if you want them to remain outdoors year round. Very large fiberglass pots are winter-safe and plants weather well in them.
2. Another designer trick is use the ceramic decorator pot but use it with the pot-in-pot method. Plant your perennial in a plastic pot and insert that into the ceramic pot. Use wood chips between the pots to insulate and to keep your ceramic pot safe from cracking. Important to note, these type of containers are better left outdoors under the protection of a porch. These pots can be stored in an unheated garage if cover cannot be provided. The wood chips offer decent protection against freeze-thaw, but you may not chance it filling up with moisture that will freeze and expand. Sometimes the drainage hole on ceramic pots gets clogged and that allows in rain or melting snow. I did this one time and luckily the pot did not crack when I brought it in to thaw. Best on a porch if left outside. Clay, glazed and porcelain types of pots are susceptible to breaking in the winter so these would be likely choices for the pot-in-pot method. After the first couple of frosts, move them to the garage if not left on a porch.
3. Another useful tip for keeping plants over winter outside is to use plants two zones hardier than the zone where you live. I live in zone 6 so that means a Zone 4 plant would work well in a container here. I planted monarda, coreopsis, tall pholx, and goldenrod that made a great comeback after the long, cold winter of 2014. And don’t forget the bulbs. Great plants to see come Spring if handled so they don’t get water-logged in Spring.
4. Do not fertilize them over winter, but do keep them moist. If the soil goes completely dry, the plant can die of desiccation. Use a good quality soil-less potting mixture. Be careful with over-watering bulbs though.
5. In spring, cut the perennials back and move them outside if having wintered in the garage.
6. Fertilize them during the growing season. I use Scotts slow release, Osmocote.
7. This pot-in pot, or fiberglass pot method works planted with bulbs also. Just make sure they do not get too wet come spring.
In Fall, you can always just transplant the perennial or bulbs back into the garden. When I divide plants in spring, I mix up perennials, bulbs, corms, and annuals for a potluck display. It is fun to combine plants and see what happens.
But what about bloom times?
The trick is to use perennials that have good leaf retention or color through the growing season. If they bloom for a long time or rebloom that is a real bonus. Some plants that stay attractive after flower are Heuchera, Hydrangea, Hosta, Agastache ‘Blue Fortune’ or ‘Bolaro’, Monarda didyma ‘Pardon My Pink’ and ‘Raspberry Wine’ and Phlox paniculata to name a few. A few are quite tall, but cutting back in late May controls and shortens their overall bloom height by mid-summer. I cut back Monarda and Goldenrod.
Perennials that bloom a long time and are nice in containers are Coreopsis, Caryopteris, Achillia, Asclepias, Leucanthemum, Symphyotrichum, geranium, among many others.
What you can do while waiting for the perennials to bloom – add some colorful annuals like, Salvia longispicata x farinacea, Salvia farinacea, or Salvia spendens. These taller annuals help support the taller perennials. If you want some spiller plants try Verbena Superbena or other trailing varieties. So many complimentary choices to name in annuals. Make sure to add those fast growing self-seeders too.
And don’t forget to use summer bulbs and tubers. I have gladioli and Turk’s Cap lilies paired with pretty annuals and miniature Monarda. By season’s end you should have some pretty containers. Yes, it does take time for the perennials to bloom.
I have a hydrangea paired with Hosta, Painted Fern and Torenia for shade. The hosta and fern should be a nice “ground cover” to the hydrangea. The Torenia adds season-long, low-growing, spilling color. It takes by mid-summer for these to bloom nicely, but the annuals help span that gap.
I always make sure the containers have something for wildlife too. Just about any plant can be potted up for summer. Herbs make great container companions and pollinators love, love, love herbs.
I highly recommend using trees, perennials, herbs, bulbs, shrubs, annuals, and plants for pollinators in containers.
I myself do not look for instant gratification and will wait until the plants reach their climax. Try mixing and matching from your garden. Just think of all the money saved when you can move your container plants into the garden instead of tossing them out season’s end.