I've tried growing geraniums from seeds several times. I've gotten plants to grow and bloom, but they never develop strong, vigorous, rapidly growing stems. Plants I buy or start from cuttings do, but my ones from seeds do not.

Any idea what I might be doing wrong? (The seeds have been both bought and saved from store-bought plants. And these are not the hardy geraniums but the one most commonly having reddish orange flowers.)