Please advise when the following should be planted — early in the spring or after May 24th?
– Boston ivy
Toronto is no longer in early spring – and euonymous (groundcover, shrub or vine) and Boston ivy can be planted now. The soil is warm enough for them and they can handle some cool weather if it comes. In fact, the last frost date in Toronto is now May 9, not May 24. This is an average of 1981-2010 temperatures calculated by Environment Canada, and there may be variations depending on topography and local weather. But even if there were to be a light freeze, it would be unlikely to kill these plants. (Some that should be planted after the last frost date are heat-needing annuals like tomatoes and peppers and basil.)
Most other perennials can also be planted immediately. However, it is a good idea to “harden off” container-grown perennials for a week or so before planting them. Some have lived in greenhouses for their entire life and may not yet be used to the outdoors. Hardening off means keeping them mainly in the shade and only gradually giving them full sun to prepare them for their spot in your garden.
Your plants will be happier if they’re planted when the weather is cool and the ground is moist. You don’t want the roots to dry out, so the ideal time is when the sky is overcast. If it’s a very sunny day, plant in early morning or evening when the location is in the shade.
When you plant the iris depends on what kind it is. Different types of irises are planted at different times of the year. I assume that the type of iris you’re planting is a bearded iris – and therefore the best time to plant is late July or early August. Bearded irises can be successfully planted in spring, but there will be fewer flowers the first year. To determine which you have and when you should plant it, see:
And here’s information from the Ontario Iris Society:
For more information on planting perennials see:
And here’s some more detail on spring frost-free dates: