Yellow leaves are a sure sign of overwatering. Reduce the watering of the plants. Basil does get woody stems once they are mature. Your not harvesting stems, but the leaves. Overwatering is the biggest killer for plants. Not only does it weaken them, but increases bad bacteria levels in the soil. Adding a mulch can harm these as it could contain all kinds of stuff to color it or make it kill off and reduce weeds. Most herbs are weeds, so the mulch may be affecting them. Herbs do much better in poor soil with very little necessary fertilizer. My marjorum was started from seeds in April and I have planted it outside last week. Its just now getting use to its new surroundings.

Thanks for the comment on the basil stems. However, I am not over watering the marjoram. Water was stingy last year with the drought and this year there has been ample rain. Quite possibly I should have my soil tested as I never had this problem in the first few years. I try to keep the soil organic and put in some compost each spring, but I am baffled as to why the marjoram looks sickly and not a nice healthy green. Again, perennials are quite happy.

Here, in my area, I found that my soil had virtually no iron. The top soil was high quality and was applied many years ago, and we always had a decent garden. About 5 years ago I decided to get soil tests done, and took samples from all over the garden area which is 2000 sq.ft. which is just for the vegetables. The tests came back indicating that iron was not available to plants. I found that the blacker the soil, the less iron it contained. That year, I applied a 50 pound bag of iron sulfate as well as 50 pounds of lime to counteract some of the extra acid iron sulfate leaves. I didn't do a soil test the following year, so I decided to also concentrate on humic acid, and many other minerals besides iron. That year, I applied a large dose of humate and iron again. That was 4 years ago. This year, I had soil tests done again and was amazed that the iron level was just normal, but nitrogen was extremely low and was now needed. That told me to put down two kinds of nitrogen, one is bird feather meal and the other is dried blood meal. These two should bring up the low nitrogen level slowly. Since adding the iron, I have not lost all my tomatoes to septoria leaf spot, and many of the other vegetables like cucumbers and squash are really great growers. I tried using those home test kits for NPK and pH, but they were never quite accurate enough, compared to what a lab shows. In any case, I always make a point to rotate crops and plant winter rye in fall, so it will produce natural nitrogen. Last years planting of rye grass was hindered due to the fat we had excessive rain and was planted a bit too late to fully germinate. Even for that, the birds were feeding on the rye seeds as well, and stripped most of them.

Thanks, you brought up some good points on how soil components interact. I agree with you on the home tests. Quite a few years ago my husband bought me those test kits with prongs that you can test the soil pH, of course accuracy depended on soil moisture. There is no replacement for professional soil testing. I will have the soil tested, but am not sure if I can affect plants this year, but it will give me a start for next year. I will probably pot up some marjoram with the expectation it will grow well. This is one of my favorite herbs for summertime cooking with garden tomatoes along with basil, thyme--oh, heck, I could go on and on about fresh herbs!!