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Cilantro grows very quickly no matter how you start it. It only takes around 4-6 weeks for cilantro to go from seed to harvest. However, seedlings in starter pots or grow kits may be ready to harvest in only 2 weeks. That said, cilantro grown from seeds rather than transplanted seedlings usually grows better and lasts longer. This is because cilantro has long taproots that don't like being disturbed (as happens during re-potting). Therefore, you have to decide whether it's worth saving 3 weeks or so of waiting in return for cilantro that may be less abundant and flavorful. At this height, the seedlings have a nice head start toward their ideal harvesting height of 6 inches (15cm), but the taproots still aren't too large. This makes the chances of a successful re-potting much higher. Add enough indoor potting mix to the new pot to make up for the depth difference between it and the cilantro's current pot (make your best guess). Try to pop out all of the soil in the current pot, if possiblework around the edges with a plastic knife to loosen the soil if needed. Place the soil and cilantro seedling in the new pot, then add potting mix around the sides to fill in the gaps. Spray the soil to moisten it after the transfer.
Plant seedlings instead of seeds to get fresh cilantro even quicker. Buy starter pots or grow kits with 2 to 3in (5.1 to 7.6cm) seedlings. Transfer the seedling and soil to a 12in (30cm) deep pot.