My definition of a volunteer is a plant that joins the garden of it's own free will. Of course weeds do that, and you want to edit them right out of the garden. But there are those that you want to stay, that will actually contribute to the effect. I'm a fan of volunteers. In my vegetable garden I rely on them. Cilantro, Parsley & Arugula do a wonderful job of coming back year after year. I like their flowers so I let them flower and go to seed, then I distribute the seed where I want them next year. Last year I had 3 different kinds of squash & I didn't plant one seed. I'm sure those came from my compost. I don't even remember eating a Patty Pan Squash. It was a lovely surprise. A friend gave me some Tomatillos. I never have to buy plants. They come back year after year. My Hispanic friends say mine are the best. Did I mention Purslain. It's really quite delicious. In my small greenhouse Cherry Tomatoes come back every year. I just need to be observant; edit what I don't want and keep what I do.
For color I love Johnny Jump Ups. They do a nice job of adding color to my vegetable garden. Now I have Allysum volunteering,too. I cannot complain; they offer some fragrance, as well. That yellow leaf Tansy comes back every year. I just take out what I don't want & leave what I do want. Hey I'm weeding anyway.
In my flower gardens the native Bleeding Heart does a wonderful job of filling in empty spaces. They like the shadier side of the garden. I saw that my Lambs Ears volunteered over in my neighbors garden. I also saw Arabis over there. I think my neighbor likes the addition. Now we all are aware of California Poppies and they can be a bit of a nuisance but they are so easy to pull out. I have all kinds of poppies in my garden. Reds, Oranges & Purples. They came from somewhere. I didn't seed them. One plant that I love that comes back from seed every year is the Datura. It's leaves smell like peanut butter. It has a beautiful big white flower. I must warn that I think some part of the plant is poisonous. I would keep them away from children.
It takes a veteran gardener to recognize the little seedlings. This is one time when a relaxed weeder pays off. Wait..... Of course, I have cultivated some very large weeds. I learn. When I was renting many years ago and I would leave to move to my next spot for many reasons like school and such, the following renter would tell me that they had a reasonable garden without doing anything but water. That was one of my best compliments.