Will Agastache Grow in Clay Soil? (Important Warning!)

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Agastache (Agastache foeniculum), also known as Hyssop or ‘hummingbird mint,’ is a perennial herb that produces clusters of nectar-filled flowers that hummingbirds adore. Though it is native to the deserts of the US and Mexico, you can also find it growing across Europe and Asia. However, Agastache won’t grow in just any type of soil. 

Agastache will grow in clay soil, but it will not flourish. It prefers sandy, fast-draining soils to moist, fertile ones. Too much water and nutrients will make the Agastache grow riotously and then die off after only one season of blooming. In desert soil, they will bloom seasonally for years. 

This article will explore the best soil type for Agastache. I will also include information about how to fix clay-rich soil so you can plant Agastache in your garden. 

What Kind of Soil Is Best for Agastache?

The best kind of soil for Agastache is soil with low organic content and low moisture retention. Like other desert plants, Agastache prefers infrequent watering and only moderately fertile soil. 

When soil is too moist, it becomes anaerobic or oxygen-deficient, which suffocates the roots of the plant. Suffocated roots end up with root rot, which can stunt growth and potentially kill the plant. 

When the soil is too fertile, it causes the plant to grow quickly and extensively during the growing season, which exhausts the plant so much that it will often die over the winter and fail to grow back the following spring. 

How To Grow Agastache if Your Garden Has Clay-Rich Soil

If the soil in your garden isn’t right to support Agastache, no worries! Even if you have clay-rich soil, you can still grow this attractive plant in your garden using pots or raised beds. 

If you’re not sure how much clay there is in your garden, you need to test the soil quality to see if it can, in fact, support Agastache. 

Test Soil Quality

Here’s how to test the quality of your soil:

1. Dig a hole in your garden big enough for an adult plant. Agastache grows to be about two to four feet (0.61 to 1.22 m) tall and 12 inches (30.48 cm) wide, so your hole should be at least 18 inches in diameter and 18 inches deep (45.72 x 45.72 cm). 
2. Fill the hole with water and wait for the water to drain out. If it takes more than 20 seconds to drain, the soil is not appropriate for Agastache. 

Grow Agastache in Pots

Agastache grows quite well in pots, provided you give it the right soil, water, and light parameters (source). In general, it needs:

• Well-draining potting soil
• Pots with drainage holes
• Repotting every two to three years 
• Watering only when soil is dry
• Full sun or minimal shade 
• Yearly treatment with a balanced 10-10-10 fertilizer 

Read on for more details about each of these needs. 

DIY Soil Mix for Potted Agastache

Potted Agastache benefits from moist but fast-draining soil. Commercial potting mixes can be too rich and moisture-retaining. In order to make them more beneficial to Agastache, I recommend adding one part inorganic material to three parts soil. 

Inorganic soil additives for improved drainage include:

• Perlite
• Vermiculite
• Sand
• Gravel
• Pumice
• Volcanic rock
• River stones

However, you should adjust the ratio of soil to inorganic materials according to the climate of your area. For extremely dry areas, decrease the soil to a ratio of 4:1. For very wet areas, increase the inorganic materials to as much as 1:1 (source).

Alternatively, you can bring your Agastache inside during peak heat or rainy seasons and place it in a window that gets plenty of light.

Pots for Agastache

When you bring your Agastache home from the nursery, it will likely need immediate repotting. However, repotting outside the growing season isn’t recommended as it may cause undue stress and shock to the plant. If it’s still spring or early summer, go ahead and repot.

There are two ways to tell if your Agastache needs repotting:

• Roots are growing out of the drainage holes at the bottom of the pot.
• You can pull the pot away from the plant and see more roots than soil. 

Choose a pot that is only two to three inches (5.08 to 7.62 cm) larger in diameter than the pot the plant came in. You may be tempted to use a larger pot, but doing so won’t benefit the plant. 

Excess soil in the pot retains water, which results in overwatering and root rot! Once you have repotted the plant, you shouldn’t need to do so again for at least two years. 

Light for Potted Agastache

As mentioned above, Agastache likes full sun. However, some varieties have lighter leaf coloring, and these benefit from partial shade in the heat of the day. 

No variety of Agastache will be significantly damaged without shade. However, the hot, direct sun can result in bleaching and discoloration of the leaves in certain varieties, such as Korean mint (Agastache rugosa), also known as ‘Golden Jubilee’ Agastache.

In addition, even the most robust Agastache may singe if left outside in extreme temperatures over 95 degrees Fahrenheit (35 degrees Celsius) for extended periods. 

For this reason, I recommend moving potted Agastache to a partially shady or shady area during extreme heat waves.

Fertilizer for Potted Agastache

Like most desert plants, Agastache doesn’t really need to be fertilized. However, applying a single dose of slow-release 10-10-10 fertilizer to the soil at the beginning of each spring will boost overall growth and bloom production (source). 

However, don’t fertilize your Agastache in its first year, as this can burn the roots, cause the plant significant stress, and result in stunted growth later. 

Use Raised Beds

Your other option for growing Agastache if you have clay-rich soil is to grow it in raised beds. These sit above the ground and allow you to provide the soil and drainage appropriate for Agastache to flourish. 

Before you start, however, it’s important to decide exactly where you want to put the beds and how big they will be. To support Agastache (and most other plants), you need a raised bed of around one foot (0.30 m) deep. The other dimensions are up to you (source).

There are two ways to install raised flower beds: 

• Purchase prefabricated beds (raised planter boxes). 
• Build your own raised beds.

If you only want to install one or two raised beds, purchasing prefabricated ones is the simplest choice and requires the least labor. However, it can be quite a bit more expensive than building your own raised beds. 

I recommend the FOYUEE Galvanized Raised Garden Beds (link to Amazon) for those who have the space. See our

On the other hand, if you’re thinking of making your own raised beds, see our article on the best wood options when building a raised garden bed.

Also, check out the detailed tutorial from the video below. It will give you a good idea of where to start and how much work it entails. 

How to Build Durable Raised Garden Beds (Planter Boxes)

Conclusion

Agastache, or Hyssop, is a flowering desert perennial that produces fragrant, nectar-filled flowers, which hummingbirds adore. 

It can be grown just about anywhere there is full sun and well-draining soil, including the following:

• In the ground
• In pots
• In raised beds

However, clay-rich soil is not good for Agastache, as it holds onto water and nutrients. While Agastache will grow in clay-rich soil for a while, it will eventually die from over-watering or overfertilization.

Recommended Reading:

• Can You Grow Agastache in the Shade? (You Need To Know This!)
• Does Agastache Have Deep Roots?
• How To Take Agastache Cuttings? The Complete Guide