I bought a mandevilla last summer, overwintered by pruning back and keeping in a cooler but sunny window, hardened it off before placing it in a morning sun place. Fed it fertilizer and even tried the age old epsom salts trick. Nicely green, lots of growth and shoots but no blossoms. When I pinch off new growth, am I pinching off new blossoms or do they bloom from the nodes? After the recent heat wave, I thought it would bloom for sure but no signs of anything yet. Ideas?
You appear to be doing almost everything right. However, as Mandevilla blossoms on the current year’s growth by pinching off the new growth at this time of year you are encouraging a bushy plant but also pinching off the growth that would develop flowers. You should prune your Mandevilla only in the autumn. At that time cut back most of the new shoots to encourage the production of more for next year.
There are a number of prior enquiries on the Toronto Master Gardener website relating to Mandevilla which you might check. It’s easy to find previous questions and answers on the website – just go to the Toronto Master Gardeners home page and enter the search term (e.g., “mandevilla”) in the search box under “Find it here”, on the right of the page. There is also a very useful fact sheet on growing Mandevilla at the Clemson Cooperative website at: https://hgic.clemson.edu/factsheet/mandevilla/
While you may not get many flowers this year, as you have managed to overwinter your Mandevilla with proper pruning you can expect to have more success next year.