Can I spray something like Round-up to get rid of fennel, grass, oregano, and lemon verbena that are in areas I'm not wanting them to be in? Or do I have to dig all this out?
Yes, you can or you can spot treat with white vinegar instead.
I have discovered mushrooms growing all over my herb garden. Since I do not know if these mushrooms are poisonous or not, is it safe to eat the herbs and other vegetables growing in this area?
No, these are not safe to ingest and in fact, many types are extremely poisonous. I would recommend getting rid of them. These articles will help and can be applied to those in the herb garden as well:
Both my Rosemary and Thyme plants have started turning brown. Is this because of too much rain, as I had them on my deck for 2 days and it rained both days? Plants are still in pots that I bought them in. Does this mean my plants have died or is there something I can do to revive the plants so I can use them in my kitchen?
It could be from too much water, but that would only be if there were no drainage holes in the pots that they came in. If they have been in standing water, that could have killed the roots. More typically though, it is from too little water. Most of the time, when you buy plants, they are root bound or near root bound in their nursery pots. They can suck the water out of the soil available to them very quickly. You need to move them into a bigger pot as soon as possible and make sure to water them daily while they are outdoors.
My parsley and basil plants in different containers are having the leaves completely eaten. Sometimes it appears as if tiny bites are taken around the edges. It doesn't appear to be the tiny round holes of the flea beetle. My backyard is completely fenced in.
Slugs are the normal culprit for this. They can literally devour plants overnight and they love basil. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/facts-about-slugs-and-how-to-kill-garden-slugs.htm
I have a thyme plant that shares a window box with a rosemary plant. In the past week, the thyme plant has changed dramatically. The leaves are yellowing and thinning out, and the entire box is absolutely crawling with those reddish-brown centipedes. There's been no change in water, sunlight, or the introduction of any new food/soil/chemicals since this started happening. I've been doing some reading, and it seems that the centipedes are PROBABLY not eating the thyme roots, but may be eating other root-eaters. But if that's happening, why aren't they taking care of the problem? And why is the rosemary perfectly fine? I'm getting food grade diatomaceous earth delivered to me on Wednesday, but I'm afraid the plant will be dead by then. Can anyone help me figure out what's going on and what I should do? Thanks in advance!!
I would isolate the infected plant and treat with Neem OIl.
How do I fix this? I am currently growing Tarragon in a pot and it has been increasing in height rather quickly. The problem is, it tends to lean towards one side so it isn't standing upright at all. I heard that this is due to the fact that herbs tend to lean towards the sun, but it still isn't straight even though I have been turning its pot regularly. What can I do for it to straighten?
Yes, it likely isn't getting even bright light. This can be correctly generally by turning the pot at least once a week.
You also can prune up the plant to have a more even appearance. Also when you need to repot, you can adjust the placement in the pot.
If the plant is healthy, I would not worry to much about an uneven plant.
There are these white spots all over my mint. What is it and should I remove it all?
Though it is a good image, it is still difficult to determine if this is a fungus or pest issue.
I would suggest using Neem Oil on the plant. Neem Oil is organic and takes care of most sucking pests and also works as a fungicide.
Neem Oil is safe for people, pets and bees.