I’m using some bloom for tomatoes.It’s 5-16-12.
It can be applied by spraying or into soil.
I got a little bit of nute burn using a 12-4-8 nute only once at 50% strength.
Since I got burn at 6-2-4 should I use a weaker mix on the bloom?
Do I try to stretch by raising light of let plants do their own stretch?
The first number is representative of nitrogen normally. So the 12 was really kinda high if you had it mixed at too high of concentration and nitrogen is usually the cause of nutrient burn, but the others can cause problems at to high of concentrations as well. Start off using the smaller recommended water to nutrient ratio mixture on the box or directions of your nutrients and you should be fine. You can slowly increase the dose or get a EC/PPM meter, they aren’t that expensive on e-bay or amazon and check your nutrient run off, the water that comes out the bottom of your soil, to be sure nutrients aren’t building up too much. The really high numbers don’t mean it will burn as long as you are properly diluting it with enough water, and if you aren’t going to use a ec/ppm meter it is best to use the most dilute recommendation according to the directions to be safe.
Latewood had a recommendation of how to step up your nutrient concentration until you saw a negative effect in the leaves and then to back off, but i couldn’t find it, i was going to link it here, but in general if you follow the instructions, and like i said maybe use the lower concentrations mixture at least you shouldn’t be burning your plants. maybe he can chime in on this one later and give you that info, but otherwise look into getting a EC/PMM meter, then you can know exactly where you are.
N-P-K ratio has nothing to do with nutrient burn. Too strong a concentration will. However; You mentioned you were running less than full strength. So; my bet without pictures to actually prove nutrient burn on leaves would be the heat of the lamp.