So I have a wonderful little garden on my rooftop. I live in the tropics, so I have a lot of sun year round. I've been very successful at growing basil, rocket, and parsley. But thyme and oregano are giving me a hard time. The problem is that the seeds don't all produce the desired herbs. For every 10 seeds I plant, only one or two produces actual aromatic plants (thyme and oregano), while the rest produce an aroma-less plant with rounded leaves that I cannot identify. Why do I have this problem with thyme and oregano only? The seeds I'm using are from completely different sources, yet they both produce that weird unwanted plant.
Oregano and Thyme Seeds
Certified GKH Gardening Expert
It sounds like it may not be your seeds, but rather the soil. Sometimes soil, even soil bought from the store, can have weed seeds in them. I would bake the soil at 350 degrees F for 15-20 minutes and then let it cool down before using. This will kill any weed seeds that may be in the soil. The other possibility is that the weed seeds are being blown into the pots. You may want to try covering the pots until the seeds germinate just to make sure nothing gets blown in.