This tomato plant I sowed from seed on April 4th in a Jiffy peat pellet, then potted up on May 5th into this 3-inch clear plastic pot w/ a mix of Jiffy seed starting mix and coco coir hydrated w/ boiling water as recommended by Gary Pilarchik of Rusted Garden.

I do believe I'm very late to begin fertilizing as it has had virtually zero nutrients so far and I'm now over a month in. I plan to provide the first dose of diluted fertilizer today. I had been holding off b/c the initial potting mix was already super saturated (boiling tap water, no fertilizer), and I was afraid of over watering. Is lack of nutrients the most likely cause for yellow leaves on this tomato plant? There are other tomato plants from the same group as this one w/ yellow leaves - not all of them, but some.