I have never had much luck growing Johnny Jump-Ups (Viola tricolor) from seed, but finally two years ago a single plant survived to maturity. Last year that lone survivor begot several offspring. This year those offspring have taught me the true meaning of the cautionary proverb, “Be careful what you wish for.” Johnny Jump-Ups are popping up everywhere, including in the cracks between the slabs of my front sidewalk. The little flowers are the quintessence of spring, but they are still blooming at the end of July. I have the feeling that even Napalm would have little effect on them.
It takes a pretty tough plant to come up through a crack. Dandelions come to mind immediately. Crabgrass and plantain don’t seem to mind such conditions. Neither do common violets and clover.
But not all plants that sprout under these adverse conditions are Johnny-Jump-Ups or weeds. There are lots of perennials and annuals that can pull it off. Many are mainstays of cottage gardens, where sidewalk or pathway sprouts are positively encouraged. Whether they grow in cracks or cachpots, these stalwarts can withstand adversity and come up smiling.
Even neat and tidy gardeners who wouldn’t dream of letting chance seedlings disturb their carefully planned layouts value such worthy traits
In my garden, one of the prime contenders for the honor of “best sidewalk plant” is musk mallow (Malva moscata), a wonderful plant that looks a little like a smaller version of its relative, the hollyhock. I installed one in a somewhat out-of-the-way location in my back garden several years ago. Like most of the plants that make it at my place, it thrived on neglect, earning the right to remain by rewarding me with lots of blossoms. By the second season it also rewarded me with lots of seedlings, many of which came up between the pavers in the brick circle that abuts the bed.
Not far from the fecund Malva is a robust bleeding heart (Dicentra spectabilis). Every year before its annual summer die-back, it spreads its seeds around abundantly. As the result I have found baby bleeding hearts coming up in pockets of the dry-laid stone wall that encloses the bed. I transplanted these youngsters to a sparsely planted shady bed in another part of the garden. I expect that within a few years hearts will be bleeding all over my property.
Then there are marigolds and snapdragons. I have never planted marigolds in my garden because I don’t really like them all that much. Nature, however, has other plans. My predecessor planted vast quantities of the chromium yellow variety, and their descendents come up doggedly every year. Since they fill up the spaces left by the die-back of the bleeding hearts, I let them stay. Prejudices aside, they also contrast rather nicely with some purple cranesbills planted in the same bed. I planted snapdragons once, during my first spring in this house. Some have overwintered each year, returning in the spring; others have self-seeded abundantly. I have one that sprouts from a cavity in the same retaining wall that harbors the bleeding heart seedlings.
Dame’s rocket (Hesperis matronalis) is another annual that needs very little encouragement to spread all over the map. To my way of thinking, the whole phenomenon is only irritating if you have taken time and trouble to create color-themed beds. Though some may disagree, there are certain colors that just don’t work well with purple.
Hostas and their kin, lily-of-the-valley, spread by tough underground roots. If you grow the latter anywhere near a sidewalk, pips will eventually emerge from between the cracks. Hostas require a bit more neglect, but not much. Left unchecked, a nice bank of hostas bordering a walkway will take over after a few years, making passage impossible.
Of course, some people try to stop the plants-in-the-cracks phenomenon by putting mortar between their stepping stones or weed killer in the sidewalk cracks. This works, at least for awhile. Eventually the mortar will crack or shift and the effects of the weedkiller will diminish. The first plants and weeds that come up after that happens are probably the most tenacious of all.
Other people take a gentler approach and deliberately plant something pleasing between slates or stones. Moss works, though some people hate it on general principles and it does tend to be a bit slippery when wet. Creeping thyme is also good, and smells wonderful when trod upon. For larger cracks, creeping phlox offers the added benefit of spring flowers. One fact though, is as immutable as blackspot in July: a plant that is deliberately sown between cracks will rarely grow as exuberantly as a plant that springs up by chance. Success or failure with this kind of planting really depends on how serious you are about beating Nature at its own game.