Broccoli plants grown in hydroponics are ready for the harvest about 60-100 days after the transplant, but it all depends on the variety you decide to grow. And if you want to start it from seeds, then it’ll take you somewhere between 100-150 days before you can harvest the fruits of your labor. The seeds first have to germinate (which takes about 7-14 days), and then you have to let them get strong enough to survive in a hydroponic system. (Many growers usually wait until 4-5 sets of true leaves appear before moving them.)