I grow a lot of plants in pots, because the dry, rooty soil of my garden (about which I complain frequently) is not hospitable to the delicate and needy. So delphiniums, lilies and even tomatoes live in big pots parked along paths and driveway.

As I water and fuss over these potted prima donnas, I often find seedlings coming up in the pot soil, everything from lamb’s ears to chervil to infant peach trees. Tiny and delicate, they are easy to ignore, and as they grow many of them look really good (the beauty of youth). They display the very qualities of leaf shape and colour that made them welcome in the garden to begin with. Sometimes these self-sown interlopers pair so well with the legitimate occupant of the pot that I don’t even think of yanking them out. (I actually have a problem yanking out any plant that’s healthy and attractive — which explains a lot about this garden).

Sometimes the pot seedlings are useful plants. All my Verbena bonariensis died last winter, so I’m happy to see a few popping up in the tomato pots and will transplant them into their own pots and eventually to spots in the garden beds. A kale plant that came up in one of last year’s tomato pots continues to thrive in the pot and furnishes a few kale leaves for salads and stuff.

But there is a Dark Side. Unchecked, the little seedling grows and grows, eventually overwhelming the legitimate occupant of the pot. I stupidly left a rose campion in one of the 2-gallon pots occupied by a “Stargazer” lily, and a plant of lamb’s ears in the other. By the time I got around to wondering why the lilies didn’t look like blooming as they had done for several summers, it was too late. An emergency repotting job only gave the lilies better quarters in which to die.

Then there was the young mullein that almost did in a bright orange lily that had lived in its pot for years. It survived, possibly because the lilies had gone dormant (but dormant looks a lot like dead, so I wasn’t sure until the lily sprouted out this spring).

Think about it — a pot contains a finite clump of soil. It’s usually improved, enriched soil, but there is only so much of it. A plant like a lily may thrive in that situation because it’s the exclusive tenant of the pot, with all of the nutrients and water available for it alone. But when a vigorous plant like a rose campion takes over, it hogs all the goodies — with predictable results.

It’s amazing how a gardener with decades of experience can ignore something this obvious. Even now — today — a self-seeded forget-me-not prospers and blooms in a pot prepared for a purchased clematis (“Pink Fantasy”). But see how pretty the tiny blue flowers are, like little stars…

I will have to harden my heart and extract the forget-me-not. They grow all over the place, but there is only one pink clematis. It did quite well this spring and I would like to see it bigger and better next year.

Finally, here are some hitchhikers that can’t possibly harm their host.

Tiny mushrooms in pot with Plectranthus cuttings