Linaria [lin-AR-ee-uh], commonly known as Toadflax, is a large genus of 150 species of flowering plants.
This genus of small bright flowering plants is, in fact, one of the largest herbaceous perennials and annuals in the Antirrhineae tribe.
The genus belongs to the plantain family Plantaginaceae and was originally placed in the Scrophulariaceae family.
They are native to temperate climates in Europe, Asia, and northern Africa.
However, the highest species diversity is found in Mediterranean regions.
The scientific name Linaria means “resembling Linum or flax.”
This is because the foliage of some of the species superficially resembles Linum.
Interestingly, these plants are regarded as one of the noxious or dangerous weeds.
Furthermore, the plants are toxic to livestock; hence, they aren’t commonly preferred by farmers, etc.
Size & Growth
The herbaceous and perennial plants of the Linaria genus have short spreading roots.
They grow decumbent stems which lie against the ground and curve upwards.
Depending on the species, the stems can grow anywhere from 12” – 36” inches in height.
From these stems, thread-like blue-green leaves sprout.
These leaves are ½-inch to 2.5” inches in length and roughly ¼-inch broad.
As for its spread, it can vary depending on the species.
However, it can cover about 2’ feet of ground space.
The seeds ripen during in fall, i.e., August to October and flower anywhere between July and October.
Since it is regarded as an invasive weed and pollinates by bees and other pollinators, it can grow very fast.
Flowering and Fragrance
As mentioned before, the plant flowers during late summer to late fall, from July to October.
The flowers are similar to snapdragons.
They can grow anywhere 1” – 1.5” inch in length and are known to attract wildlife and pollinators.
Linaria flowers grow on dense terminal racemes and contain both male and female organs.
Bumblebees, among other pollinators, pollinate the plants.
The flowers in different species range in shades of yellow, purple, and pink.
Along with flowers, Linaria also grows globose capsule-like fruits.
These fruits are roughly ½-inch in length and ¼-inch broad.
They contain numerous seeds which are released once the fruit dries and breaks open.
Light & Temperature
Linaria plants are native to temperate climates and can grow in USDA zones 3a to 9b.
The plants love woodlands and gardens and can thrive in both sunny edges, semi-shade light woodlands or no shade.
Watering and Feeding
The plants have average watering needs and are susceptible to root rot when overwatered.
Linaria is also a very drought-resistant genus.
It can grow in drystone walls once the plants are established.
These plants can spread fairly aggressively and doesn’t need much feeding and regular fertilization to grow and succeed.
Soil & Transplanting
Like many other annuals and perennial plants, Linaria also prefers moderately well-drained soil.
It can thrive in all kinds of soil, including loam, sand, and clay.
As for pH, the plants can grow in mildly acidic (6.1 to 6.5), neutral (6.6 to 7.5), and mildly alkaline (7.6 to 7.8) soils.
As for transplanting, the plants are mostly directly grown in hedges and gardens.
In North America, they have escaped cultivation and are common along sidewalks and areas with poor soils.
Grooming and Maintenance
Linaria is a weed, meaning it can grow and spread very fast. Their growth can get out of hand.
They are self-sowing and pollinated by bees aggressively.
This means if you’re growing them, you need to be avid about keeping their spread in check much like the dandelion.
Even though they are avoided by ruminants, they are toxic for livestock.
Prune the flowers back once they bloom to prevent self-seeding.
How to Propagate Toadflax
Linaria is propagated with seeds and division.
If you’re propagating them with seeds, wait for the fruits to dry out while still on the plant.
Once they do, break them open and collect the seeds.
Sow them in early spring in the area where you want to grow them, e.g., garden hedges.
The seeds will ripen in the coming fall.
The division is also very easy and is done in April or the fall.
Divide large clumps and replant them in their permanent positions.
However, it is preferable you pot them in cold frames until they root well and then plant them out in spring.
Linaria Toadflax Pest or Disease Problems
Common pest problems with Linaria include aphids.
As for diseases, Linaria plants are affected by powdery mildew.
Consult your local gardening center and choose the least toxic solution to get rid of them both.
Suggested Linaria Uses
Despite the status of being a weed, Linaria plants have several uses.
They are often used in pollinator gardens as they attract different species of bees.
They are also used as food for the larvae of Lepidoptera species like the mouse moth and common buckeye.
The Linaria vulgaris species of the Linaria genus also has medicinal benefits.
Some other uses include obtaining dye from the flowers.
And lastly, the Linaria vulgaris species is also used to make a tea used as an insecticide.