Toadflax is a beautiful flower, beloved by bees and other pollinators. However, the phrase "too much of a good thing" is definitely true when it comes to certain varieties of this plant, which are considered to be noxious invasives and are prohibited in many areas of North America. A little know-how in terms of knowing which varieties are safe to plant, as well as how to control the more exuberant varieties, is essential if you're considering growing toadflax.
Know Your Toadflax Types
Toadflax (Linaria) is a plant that is generally native to Eurasia and was introduced to North America in the late 1800s and early 1900s. There are several types of toadflax, and some are more invasive and difficult to control than others. Luckily, they're also fairly easy to tell apart.
Early introduction of more invasive toadflax in North America may have been because yellow toadflax, Linaria vulgaris, AKA butter and eggs or wild snapdragon, is historically a good plant for producing dyes and has some medicinal uses.
Unfortunately, yellow toadflax is also extremely invasive and even prohibited in many U.S. states and Canadian provinces. It is a rampant spreader, colonizing entire areas through a combination of root growth and seed dispersal. A single yellow toadflax plant can produce half a million seeds in its lifetime, and seeds stay viable for ten years.
The flowers are beautiful, which explains why so many gardeners have planted them in their gardens. They definitely look like snapdragons, and have creamy pale yellow flowers with deeper yellowy-orange "tongues."
Butter and eggs grows up to two feet tall (though it's usually much shorter than that) and has narrow, strappy leaves.
Dalmatian toadflax, Linaria dalmatica, is very similar to yellow toadflax, but it grows even larger, and has broad, heart-shaped leaves as opposed to the narrow, straight leaves of yellow toadflax. They can grow as tall as three feet, though they're generally shorter.
Dalmatian toadflax also has pale yellow blooms with yellowish-orange along the bottom lip, though this type is usually found in western regions, while yellow toadflax is more often found in the east.
Blue toadflax, which was formerly known as Linaria canadensis and now as Nuttallanthus canadensis, is one of the toadflaxes that you can feel safe growing in your garden. Native to eastern North America, it's an annual or biennial wildflower that grows 10 to 32 inches tall and has delicate purple and off-white blooms. The flower shape is very similar to the more invasive toadflaxes (making it easy to see why they share the common name) and it grows on tall, slender stems.
Like many native plants, blue toadflax can become a little weedy; however, unlike yellow or dalmatian toadflax, it won't out-compete other native plants. It's also a host plant for the larvae of the Common Buckeye butterfly, as well as a nectar source for bees and many different types of butterflies.
Blue toadflax grows best in full sun and very sandy soils, making this plant especially suited to coastal areas.
Another native variety, Texas toadflax (Nuttallanthus texanus) produces two-lipped violet to pale blue blossoms growing on stalks that reach up to 32 inches tall. Each flower has a slender spur reaching down the back side of the blossom.
Texas toadflax is an annual that grows best in moist, sandy soils and is most often found in woodland clearings or grasslands. It attracts many different pollinators and is native from British Columbia all the way down to Mexico, and can be found just about anywhere from the Pacific to the Atlantic where conditions are suitable.
Alpine Toadflax (Linaria alpina) forms dense, spreading, dwarf, and silvery tufts covered with bluish-violet and intense orange flowers. It is usually biennial; but in favoured spots, both wild and cultivated, becomes perennial. It sows itself freely and is a good option for rock gardens. Though it's not native, alpine toadflax is generally well-behaved and won't become too much of a problem.
Controlling Invasive Toadflax
Yellow toadflax and dalmatian toadflax can be very difficult to get rid of once they've established themselves in an area. They produce long runners, with new plants popping up every few inches along the length of the runner. Cutting the root usually results in more plants, and it's very difficult if not impossible to get all of the roots.
In addition to spreading via roots, they produce abundant seeds that stay viable in the soil for ten years or more. There are a few methods for getting it under control.
Digging and Pulling
Your best bet for eradicating or at least controlling yellow or dalmatian toadflax in your garden is to dig up as much of it as you can, knowing that you'll continue to see it popping up for years to come.
Regularly pulling any plants that you notice, and removing any flowers before they set seed, will go a long way toward eventually ridding your garden of it, but it will likely take several seasons of continued attention and removal.
Tilling and Solarizing
A more straightforward method (especially if you remove any desirable plants from the area first) is to solarize the entire area.
- Dig out as much of the toadflax as you can, and then till the entire area it's been growing in.
- After tilling, cover the entire area with black plastic to solarize the soil -- the intense heat beneath the black plastic will eventually kill even the most stubborn weeds and seeds. It's best to let the area solarize for six to eight weeks before removing the plastic.
- To be really sure you've gotten rid of it, especially if you had an especially robust growth of toadflax, you could go through the tilling and solarizing cycle one more time. This will bring up any roots and seeds that you may have missed the first time around.
- After this process is done, you can plant the area as normal, keeping an eye out for any errant toadflax that survived.
How to Grow Toadflax
If you decide that you'd like to grow toadflax in your garden, it's not a difficult plant to grow, and looks wonderful as part of a cottage garden or mixed border. To save yourself from some headaches later on, it's probably best to grow one of the native, annual varieties of toadflax rather than one of the invasives.
If you do decide to take a chance on growing yellow toadflax or dalmatian toadflax, you'll want to stay on top of it, deadheading when it's finished blooming and pulling any runners that aren't where you want them to be.
Light and Soil
Toadflax grows best in full sun but will also tolerate some shade.
Yellow toadflax and dalmatian toadflax aren't overly picky about soil type. Blue toadflax and Texas toadflax prefer sandy soil. If your garden soil isn't generally sandy, and you want to grow one of the native toadflaxes, amend the soil in that area with some compost and a bit of coarse sand, which will provide the light, quick-draining texture these plants prefer.
Watering and Fertilizing
Toadflax (invasive or native) really doesn't need much babying. You'll want to water them well after sowing seed or transplanting, but after that, they'll likely only need water during drought conditions.
Toadflaxes don't need additional fertilizer.
Pests and Diseases
Toadflax isn't prone to many pest or disease issues. Many of them are deer-resistant. Aphids can sometimes be a problem. Often a strong blast of water from the hose or a spray with insecticidal soap will take care of the problem.
Choose Carefully, Then Enjoy
Knowing which types of toadflax can become invasive will help you decide whether you really want to grow this plant in your garden. Remember that there are native alternatives, and though they don't have the bright yellow flowers, they have a charm all their own. Some even provide habitat for butterflies.