By the time you are reading this article, we will have welcomed spring! It’s not yet planting time here in the north, but we have had many days now where temperatures have risen above freezing, the sun has been shining and rain has fallen. Snow is melting nicely in my yard, hopefully in yours too.
I received an email requesting an article on early planting of window boxes and containers. Shannon commented that she always waits until early June to plant her window boxes and asked if there was anything she could plant earlier that would be safe in cool weather.
The first flower that comes to mind is pansies. They, along with their cousin the viola, are the flowers traditionally planted in cooler weather. Both will take a light frost of 1 to 2 degrees below zero. Other cold tolerant plants include Calendula, Dianthus, Snapdragons, Stock, Dusty Miller, and Sweet Alyssum.
Although cold tolerant varieties can handle the fluctuating temperature we typically see in our area during late April and May, they will need to be hardened off before planting. Hardening off is the gradual introduction to outdoor conditions of greenhouse grown plants.
Begin by taking them home and setting them in a cool area that will stay above freezing. Set them out for a few hours a day and gradually increase the time they are outside. If the containers you intend to plant are portable, you can plant your flowers right away and move the containers in and out.
Once plants have adapted, they can be left in place. Monitor the weather and be prepared to cover them with frost blanket when necessary or tuck them into a shed or garage as needed. These plants won’t be too happy if the temperature dips low enough to freeze them solid.
A word of caution though, watch for days where the temperature may be above zero but the windchill is below. Cold wind can damage plants too. Also, always bring in hanging baskets on cold nights and on days with cold wind. They are hanging in mid air, so more susceptible to the cold than planters on the ground.
It is often hard to achieve height and drama in a spring pot. Most cold hardy flowers are on the short side. You could collect pussy willow stems and arrange them in the middle of back of you planter to add height and interest. Outdoor battery powered mini lights would add another level of interest. You could also add a decorative obelisk or piece of garden décor on a stake for a focal point. If the garden décor you choose has a solar light built in the container would have some after-dark appeal too.
You can also purchase pots of spring blooming bulbs such as tulips and daffodils. The entire pot can be tucked into your window boxes or containers, or you can carefully transplant them. Once those flowers are finished, cut off the flower stocks and leave the foliage to die down naturally. You can then transplant the bulbs into a garden when you are ready to replant your pots for the summer.
We try to create a container that has a thriller, spiller, and filler. As mentioned above, the thriller and filler are covered, but how do you add a plant the spills over the edge or trails down the edge of the pot for early planting? Look to the perennial benches at your favourite garden centre for hardy periwinkle or other trailing plants that can be added to containers and later planted in the ground if you have space for them.