Water with plain water first before fertilizing?

[Fairorchids]

Note:

I water with a hose, pouring water on large hanging baskets for 5-10 seconds each. It takes me approx. 3 hours to water the entire greenhouse.

I fertilize with a hose end sprayer, with the dial set at 4.5. We use some 12-15 refills of the sprayer supply bottle, and the full application takes about 35-40 minutes.

That type of 'injection' can't be set low enough to do a single application, that both provides enough water, and a low enough dosage to use it in every watering.