Thank you to everyone who commented yesterday about the mushrooms. The advice was very helpful. I dug up the mushrooms to see what the soil underneath them looked like, and this is what I found:
Directly underneath the mushrooms, I found an ash-gray color in the dirt. I dug up the dirt where the mushrooms had not appeared, and that soil looked dark brown and moist. So I took it as a sign that those areas are safe from mushroom infestation. I'll keep my eyes open for additional mushrooms.
In the front yard, we didn't do the traditional SFG. We used the dirt that was there and added organic top soil to it. We should have probably done something else to the dirt, but we are beginners. Next year, I will probably need to figure out how to keep that area healthier. The front vegetable bed is also shaded for several hours in the afternoon, so this may have something to do with the mushrooms.
So far, the lettuce in the front is doing much better than the lettuce in the back. Here's a wide view of the front vegetable bed.
Above: We used to have spinach, but we didn't pick the spinach leaves until it was too late. The spinach plants had started to flower, and when it flowers, the plant basically dies for the season. Maybe next year we'll have better luck.
Below: More close-up pictures of our lettuce heads. They haven't formed into heads yet, and I wonder if they ever will. They are getting pretty large.
On another topic, Cam and I went to a nursery yesterday and found two everbearing strawberry plants. They were on sale, and one of the plants already had 2 strawberry fruit on it. I decided to do an experiment. I potted one of the strawberry plants (the one without the fruit), and I planted the one with fruit in the SFG box in the back. I'm going to monitor how each one does over the course of the summer.
Below: potted strawberry plant
Below: strawberry plant in SFG Box # 2. This was taken yesterday after it stopped raining.
I'd love to have tons of strawberries, but the season for strawberries (well, the June-bearing variety) is coming to a close. May is strawberry season, I believe. But we'll see. It'll be a fun and delicious (I hope) experiment.
Above: the strawberry plant today. You can tell one of the strawberries is gaining more color.
Does anyone have experience with growing strawberries? If so, I'd love to hear your tales.