^ Most potting composts are. You basically have three types of compost in order of high nutrient content to low nutrient content;
- potting compost: high in nutrients and for growing plants on. Too 'hot' for small seedlings and cuttings.
- multipurpose compost: contains enough nutrients for several weeks of growth, but in low enough quantities to allow you to sow seeds successfully or to root cuttings. This is my favourite since it's so versatile and means you only need one compost for germinating seeds, rooting cuttings and potting on. Buying just this saves money too.
- sowing and cutting compost: as the name implies, you can sow seeds or root cuttings and is suitable for delicate, sensitive seedlings that have issues in compost that is too 'hot' i.e. has too much base fertilizer. However the plants soon run out of nutrients and will need to be fed. This is why it's only used for seedlings or cuttings and it's often quite expensive for what it is. Beginners assume it's needed and will pay the money when in fact for 99% of the strains it's not needed at all.
It's likely that you used either a multipurose compost, or possibly a potting compost and there is enough base fertilizer in the compost to last for a number of weeks. If you are potting up - that is, growing the plant in a small pot until you see roots through the drainage holes in the bottom and then transplanting in a slightly larger pot filled with compost and so on for between 3 and 5 times - each time you pot up there are enough nutrients inbetween each pot up, meaning no feeding will be needed at all up until a couple of weeks after you switch to 12/12, when the plant starts to flower.
If you don't pot up like you really are supposed to (instead of the wrong way of transplanting a small plant in a small pot straight into a large pot of compost without any steps inbetween),
there should be absolutely no need for 'grow' fertilizers whatsoever' and the only nutrient that's needed will be a 'bloom' formulation starting from 2 weeks into flowering period after switching to 12/12. The high P and K levels in the bloom fertilizer will stimulate flowering and you'll yield more as a result.
Prelude if you don't want to buy a greenhouse because they're too expensive or for whatever reason, I would strongly recommend buying some horticultural fleece to wrap around the plants at night, since they shield them from low temps. A sheet of horticultural fleece that is large enough to cover quite a few plants should only cost you about $6, so they're very cheap. They're basically very thin layers of fleece that allow the plants to breathe easily but keep the plants nice and warm. They're extremely effective and used all throughout the horticulural industry. You need to take it off every morning though, which is easy enough (if you forget it doesn't matter at all).