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Agastache, also known as the Giant Hyssop or Anise Hyssop, is a bee-attracting plant beloved for its long-blooming purple flowers. More interestingly, the root system of Agastache has a unique pattern that contributes to the plant’s efficient growth.
An Agastache plant has a deep taproot once fully established. This taproot protects the plant against droughts and seasonal changes in the water supply. The plant also has rhizomes and smaller laterally growing roots that help support its tall shoots.
Read on to learn more about the impressive roots that grow underneath Agastache flowers. I’ll also cover problems you may face when growing them, and how you can care for them better.
Here’s Why Agastache Has Deep Roots
The deep roots of Agastache plants are a sign of how the plant evolved to thrive in dry conditions. When the roots grow deep enough, you can expect Agastache to fare pretty well against drought or otherwise dry conditions.
The original Agastache evolved in prairies and meadows, where the water supply is not considered relatively stable (source). The root system also provides extra support that allows the beautiful flowers to bloom upwards instead of falling over.
However, it’s worth noting that the plant is relatively short-lived (source). Most gardeners grow Agastache plants as an annual in colder regions because these tender plants don’t do well in areas with harsh winters.
In this case, Agastache plants don’t have the opportunity to grow their roots deep enough before they die. Gardeners typically don’t mind because Agastache plants are relatively easy to grow from seed and often bloom in their first year.
But when grown in areas with mild winters, such as USDA zones 8-10, the plant can keep coming back in spring to produce fresh flowers in the summer. Their roots then continue to grow deep enough to support the growth above.
The Problem With Having Deep Roots
While drought tolerance is a known advantage of having deep roots, there are some problems you still need to look out for. Having deep roots creates obstacles that you might need to keep in mind while planting and caring for your Agastache. Here are a few:
Not Suitable for Wet Soil
Deep-rooted plants are not suitable for growing in wet soil, such as the soil you typically find in the Eastern United States. If you grow Agastache in this type of soil, there is a significant risk of the plant developing root rot.
Plants that develop root rot can quickly become nutrient-deficient which can lead to a variety of symptoms. They can start to get yellowish and their growth would be stunted (source).
For more information see What Are The Signs Of Overwatering Plants?
Doesn’t Do Well in Pots
If you intend to grow Agastache as an annual, growing them in pots is actually an excellent idea. The plant takes time to develop its taproot and will likely grow well in an average-sized pot. A pot at least 12-inch (30 cm) wide and 12-inch (30 cm) tall should suffice.
However, growing them as potted perennials can be challenging. The root system needs a lot of space to grow deep, and most planting pots are too shallow for this purpose. Their lateral roots will also struggle to spread, causing stunted growth above.
Incompatible With Humid Weather
Another obstacle you might find when growing Agastache is planting it in humid weather. Because the plant has developed to withstand periods of drought, it didn’t develop the necessary defense mechanisms against humidity in the air and the soil.
The roots won’t be able to absorb enough water for the plant to thrive properly, and you will have stunted Agastache flowers that may or may not bloom.
Pro Tip: Original varieties such as the Blue Fortune will do slightly better in humid weather than other varieties of Agastache (source).
Caring for Healthy Agastache Roots
As with any perennial plant, you’ll enjoy your Agastache flowers much more if you learn how to care for them well. Of course, you will need to provide the right balance of sunlight, water, temperature, climate, and optimal soil conditions.
Here are a few guidelines you can follow when caring for Agastache plants:
Optimal Temperature and Humidity
High temperatures are usually not a problem for Agastache flowers, but they don’t like humid weather. It’s best to plant them in a spot in your garden that gets a lot of sun during the day and maybe even in the afternoon.
On the other hand, low temperatures can significantly affect the plant’s productivity and longevity. Aim for evening temperatures above 55 °F (12.8 °C) and daytime temperatures above 65 °F (18.3 °C) (source).
Keeping these things in mind will ensure that your plant develops deep and healthy roots.
Adequate Water Requirement
Young plants love to absorb water, so you’ll need to water them regularly. However, you will need to hold back for fully established plants because you don’t want to create wet soil that leads to root rot.
Agastache plants that have had at least two blooming seasons become more drought tolerant as the years pass by. They can go for one to two weeks without water in spring. Depending on the temperature and soil conditions in your area, you may need to adjust the watering schedule.
You can refer to the watering guide below:
- For young plants with shallow roots: Water when the upper inch (2.5 cm) appears dry.
- Mature plants with roots at least 12 inches (30 cm) deep: They can survive even when up to three inches (7.5 cm) of the soil is dry.
- Potted plants: They dry out much faster, so you’ll need to water them deeply when the upper inch (2.5 cm) of the potting mix is dry.
The Best Soil for Agastache
This plant prefers low-nutrient soil over high-nutrient soil. Soil rich in potassium and phosphorus will encourage your plant to bloom profusely in the summer. As a result, your plant will lose vigor much sooner and be less likely to bounce back the following spring.
As such, make sure that the soil is not too rich, and you can guarantee your Agastache will thrive for several years. Potted perennials can do well with a single application of half-strength slow-release granular fertilizers in mid-spring to prevent fertilizer burn.
The deep roots of Agastache flowers are both an advantage and a disadvantage, depending on how you treat the plant. Do it right, and you’ll get to see their pop of color and smell their fragrance when they’re in season.
It tolerates drought exceptionally well, so you can enjoy those blooms even when you forget to water them for a few days. However, keep it away from wet conditions and shallow soil to allow Agastache blooms to thrive and last longer.