Any plant growing where it’s not supposed to be might be called a weed, but there’s more to it than that, as horticulturist Sally Heiney showed during a Sunday program at the N.C. Botanical Garden.
“ ‘Weed’ is a loose term,” she said. “Lots of weeds are wildflowers. They grow here naturally.”
But a pretty wildflower can become a weed if its seeds float over into a farmer’s field and start choking out the soybeans.
Heiney presented “Weeds 101” to an audience who mostly had the standard notion of weeds as undesirables.
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“I have tons of weeds in my yard and I’d like to get rid of them,” Celeste Huntington said.
Betsy Underwood, a volunteer at the botanical garden, said she wanted to find out as much as she could about how to get rid of weeds and encourage flowers.
Heiney spent more than two hours showing and describing a variety of weeds, and offering advice on keeping them under control.
“One of the things about weeds is, there are always going to be weeds,” she said. “You spend a lot of time chasing them and you only have so much time.”
One measure is prevention, and knowing where weeds may come from. “Whenever you buy a plant anywhere, knock off the top half inch of soil,” she said – weed seeds could have come with the plant.
She also mentioned tilling the garden at night – some weeds won’t germinate except in sunlight. Tests in some places have found that turning the soil at night cuts weed growth as much as 80 percent.
Winter is a good time for weeding out plants that have deep roots, such as wild onions. Alternate freezing and thawing makes soil loose so weeds come up easily, roots and all.
The steak knives in your kitchen make handy weeding tools – slicing back and forth just below the ground surface cuts off the growings tips of weeds, weakening roots deprived even temporarily of photosynthesis.
With unwanted vines such as English ivy, creeping Charlie or honeysuckle, Heiney suggested digging up an edge and then rolling the vines up like rolling a carpet. Because the vines grow in a tangle, they almost pull themselves out as you go and may expose other plants you’d like to keep that have been hidden underneath.
Plus, it’s much easier than pulling up vine by vine by hand.
“If you rip it and rip it and rip it, it’s 20 times the work,” she said.
A close familiarity with your own yard and garden are basic control measures.
“That way, you’re really seeing, really monitoring what you have,” she said. And it’s important to know weeds – how they grow, when they flower, what the different windows of opportunity are for cutting, digging or spraying. (By the way, household vinegar is an effective weed-killer, she pointed out.)
Knowing weeds also informs decisions of what to attack, and what to leave alone. Some plants generally considered weeds may be filling important ecological roles.
Violets, for example, are vital to the life cycle of some butterfly and moth species. Pokeweed berries are winter food for sparrows. Honeybees, which have been in serious decline for several years, thrive on the flowers of some plants dismissed as weeds, according to Heiney.
Controlling weeds, and understanding them, is a discovery process, Heiney said. An unfamiliar plant you spot may be a problem, or “it may be something you’re waited for all your life and you can encourage it.
One reason for being selective when it comes to weeding is encouraging biodiversity, she said. Some weeds are native to the P iedmont and if they are not allowed to grow their value is lost to the birds and insects and microorganisms that evolved to depend on them.
“The more of the native ‘weeds’ we can incorporate back ... even if somebody else has called them ‘weeds’ – everybody benefits,” she said.