It can be easy to allow a volunteer plant to grow in a garden. You can have many reasons why this will appear to be a good idea. You might see it as free food, or maybe the birds love it. It attracts bees and butterflies. In general, life attracts life. But the word GARDEN as a noun has a very specific meaning. The word comes to us from the Franks as gardô which means “walled ordered plot”. It’s not an open field. It is a place where humans ambulate in a controlled systems of microclimates and ecosystems. Generally we seek order in a garden so as to maximize food resources. This requires that we treat the garden plots with care and nutrients and to do that one must be able to get around to control weeds. Weeds and pests are seeking access to the same resources as your plants.
At Mezzacello when I first started my garden I grew a special pollinator garden to attract beneficial bees and butterflies. Now of course I have the larger pollinators landing strip to the east in the formal gardens and the wilds. But the ghosts of some of those beneficials still appear. Usually its tomatoes but this year it was demon fennel. I have nothing against fennel. Fennel is in the carrot family with feathery leaves, an anise flavor, every part is edible, and usually it has a nice crisp round root ball that grows at the base of the plant. But demon fennel that grows up between the bricks in your walk way between lasagna beds. That right there is the antithesis of “garden” that is war.
I let the fennel grow because it was pretty and harmless and the bees did love it early in the season. But fennel produces copious amounts of seeds and when it is not properly tended with appropriate soils or growing substrates it becomes an invasive weed. Tortured by the cramped bricks it puts all of its considerable energy into growing down with a tap root and up into the leaves. The plants bolted in a matter of a few weeks into a 2.5 meter behemoth that was blocking sunlight and stealing water from the southwest beds where I was growing turnips and beets. Now I had to manage it. To do that I had to destroy my brick, sand and mulch walkway. Those plants were entrenched and were making it impossible to move around and weed appropriately. Once I removed all the fennel, I realized I had a really bad rye grass and belladonna outbreak along the fence line to deal with. A garden gives life, but demands order. In an enclosed ecosystem this can have really important and dangerous ramifications.