I really do not think that you can put your plants outside overnight in northern ontario until maybe june 10th. Unless unless you can cover them at night? The fertilizer you mention sounds good for flowering! Hmm if the best secure spot you no of is near the pine trees try working the ground up a bit and watering the crap out of the area high a high ph water and and a couple cups of domolite lime. work that in as well. Might work and raise ph.
good luck hope this helps