There are a few reasons your marijuana seeds may not be sprouting. You may have bought old seeds. Old seeds can take forever to germinate and grow into a plant. You may have planted the seeds too deep. Cannabis seeds need light to germinate, so if you bury them too deep in the soil, they will not get enough light to grow. You may have planted the seeds in an area that is too hot or too cold. The cannabis plant needs warm temperatures (about 70 degrees Fahrenheit) and lots of sunlight to grow indoors and outdoors. If your plants get too hot or cold before they grow, they cannot survive as well as they could otherwise.