Managing Weeds

Garden renovation can bring multiple rewards. Re-thinking your landscape can yield opportunities to exercise one’s creativity, pursue recent insights into botanical combinations, add exciting new plants, dismiss too-familiar vignettes in favor of new horticultural frontiers, and discover excuses to “shovel-prune” under-performing plants.

The process also includes several downsides: lots of work, heavy expenses, and the frustration of waiting for the new landscape to develop into its promise.

There’s another downside to consider: enabling the germination of unwanted plants in the weed seed bank.

Experienced gardeners know that their soil harbors an inventory of weed seeds that are lurking a few inches below the surface, waiting for a little sunlight, a little moisture, and presumably a little oxygen. Given those prerequisites, they will burst into growth and the production of another generation of seeds.

The weed seed bank developed in a variety of ways. It might have come from last season’s weeds, or the careless importation of contaminated soil or potted plants, or the tireless efforts of birds, who we suspect are spending their days moving seeds into our gardens. And there’s the wind, which transports the lighter-weight seeds to gardens where they typically are unwanted.

Some itinerant seeds are actually welcome in our gardens, but they are out-numbered by the weed seeds.

Regardless of the origins of the weed seed bank, the important fact is that the seeds are not far from the surface, and they can retain their vitality for years.

Given this reality, consider what happens with a garden renovation project. In my garden, this process included cutting down fifty feet of large shrubs and grinding their roots, digging and replanting scores of native irises, relocating a large number of bearded irises, and planting dozens of new plants from one-gallon and fifteen-gallon pots.

All of this activity has churned the soil and consequently liberated my garden’s weed seed bank. A clear contrast in weed populations can be observed between the disturbed and untouched areas. This requires hours of weeding, with the optimistic goal to pull weeds before they set seeds for next season.

An activity that parallels garden renovation is the sowing of seeds for annual plants, whether for edible or ornamental gardening. The usual advice for planting seeds is to loosen the soil, scatter the seeds, rake them in, water them in, and maintain moisture while the seeds germinate. If your goal would be to activate your weed seed bank, you would go through exactly the same steps!

The Theodore Payne Foundation for Wild Flowers and Native Plants has sent the wildflower seeds I ordered and provided recommendations for leaving the weed seed bank in its dormant state. The basic strategy is to disturb the soil as little as possible and preferably not at all. The Foundation recommends digging or tilling no deeper than three or four inches. Better still, after clearing the planting area of existing weeds, rake the soil gently, scatter the seeds, and cover them with about one-eighth inch of garden soil or light potting soil.

Despite this careful effort to leave weed seeds dormant, the Foundation adds a tip for planting wildflower mixtures: plant a sample of the seed in pots in some fresh potting soil, so you could identify which seedlings in the ground are the desired wildflowers, and which are weeds to be removed. Even when the experts are most careful, weed seeds will germinate.

Battling weeds might be an unavoidable part of gardening, but it can’t deny us the joys of renovating our gardens from time to time and growing annual plants.

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