Growing perennials in containers makes sense for northern gardeners for a lot of reasons. Sometimes you have a plant you want to add to the garden, but aren’t sure exactly where it should go. Other times, you may know where you want the plant to be placed but because of heat (about which we know a lot lately!) or other factors you decide to wait to plant it. Sometimes you buy a plant you love and realize you don’t have room in the ground. Or, maybe you just like the look of a perennial in a pretty container.
Here are a few things to remember about growing perennials in containers.
One plant, one pot. We love the look of mixed containers of annuals, and certainly you can add annuals to a perennial in a pot. Because of their size, most perennials do best in their own, private container. For size, choose the biggest container that looks in proportion to the size you expect the perennial to be in midsummer. For hostas, a 20-inch pot is a good rule off thumb, unless it’s a small hosta. Bee balm is another popular perennial for pots—a full-size bee balm will need a 5 gallon pot. The smaller varieties will do fine in a 12 or 14-inch pot. Perennials generally have larger root systems than annuals, so you want to give them plenty of room.
Follow basic care rules. Whether your container is holding annuals or growing perennials, you’ll have the best results if you follow basic care rules. Choose a good quality potting mix and add some slow-release fertilizer at planting time. If your perennial likes acid soil, adjust with sulphur or an organic soil acidifer. Place the container in the proper sun situation for the plant—sun, shade or somewhere in between. Make sure your pot drains well and give the plant regular watering, especially if weather is hot or dry. Because you will be watering the container frequently, plan to add some additional fertilizer midseason. Watering flushes nutrients from the soil and your plants will need a boost come July.
Plant with design in mind. There are many creative ways of growing perennials in containers to enhance your garden design. Set the container in a garden bed to brighten up a spot that’s going through a “green phase.” Shade perennials, such as coral bells, offer more leaf color options, making them perfect to set in a bed filled with hosta. Group pots of perennials on a front step, then rotate them in an out as they go through their bloom cycle. Use dramatic pots to bring unity to perennials in a group.
The biggest question with growing perennials in pots is how do you overwinter them? As we move into fall, you have a few options of what to do with your perennials.
Option 1 is to just leave the plant out, but that won’t work for a lot of plants. The general rule is that for a perennial to survive in a container outside it should be hardy two zones colder than your zone. So, a USDA Zone 2 perennial would make it through the winter in zone 4. (Yea, there are not a lot of zone 2 perennials!)
Option 2 is to “plant” the plant in its pot. This works best if you use plain nursery pot inside a decorative container. In fall, dig a hole in your garden to accommodate the nursery pot, plant it there and water it in. Add a bit of mulch and leave it until spring. It should do fine.
Option 3 is to move the perennial and its container into a slightly warmer (but not warm) area, such as a cold frame or unheated garage. I’ve done this successfully with lilies, but have failed with other plants. Again, give it some water, and leave it alone through the winter.
Option 4 is to find it a permanent home and plant it in the garden. Do this early enough in the fall to give the plant a chance to root in. Late September or early October is best, though I’ve planted perennials in early November and they have survived.
Option 5 is to thank your perennial for its service and beauty and toss it. I know many gardeners have trouble with this option (“It’s a perennial! I paid good money for it.”) but it’s there. If you decide you don’t want it in your garden any longer, you could also give it to a friend who does.