When to start feeding in sunshine mix #4/promix HP

Hey all, just some background: About 2 weeks ago I planted some autoflower seeds in 7 gallonpots of sunshine mix #4 outdoors. According to the company “You should start your own feed program within 7-14 days of planting or seedling emergence.” I initially watered in about a gallon of just 100ppm tap water. Growth has been sluggish and I’m not sure if I should feed yet as the medium ppm is 1000 right off the bat. I’ve also heard that it takes about two weeks for the lime in the medium to buffer the pH after the first initial watering. The weather has been raining and cold at night (zone 3b) so that could be a major factor.

When do you promix/sunshine growers start feeding your seedlings? And at roughly what ppm/EC?

I’ve only ever used these mediums indoors and it’s been so long that I can’t remember. Any suggestions are helpful. Thanks!!!

I grow with ProMix HP and feed Mega Crop one part.

Right from the start I feed 1g/gallon and roughly follow their feed schedule right to the end...

Cheers

I'll feed them right away with a very low ppm a+b until true leaves. 300-400ppm they don't need much in the beginning. You can use plain water once or twice between feedings. Don't soak the soil. Just a wee bit at first until roots develop.
It's better to use amendments in promix outdoors, that way Everytime it rains the plants are getting fed. Otherwise it's a battle between mother nature letting pots dry before watering with nutes again.
Try to top dress with about an inch of worm castings for a start. That'll get em going.
Good luck!