It is now about three weeks before the last frost. In other words, you can start new plants from seed now, unless of course, you have already done so. Three weeks is a good time to start seeds because you can use cheap Jiffy pellets which support a root system quite easily for three to four weeks before transplanting.
If you started Jiffy Pellets earlier, have no worry. Your options are to transplant, or, simply put them in a more spacious environment where you can keep the roots out of light and flood the roots with nutrients. Essentially, this can be done with simple manual hydroponics or by using a flood and drain system.