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Agastache Ultimate Growing and Care Guide

Agastache is an incredibly easy plant to care for, with few pest issues, fewer habitual diseases, and unlike its big brother, mint, won’t spread through the garden on runners or rhizomes.

And a big bonus, is that the entire plant is as edible as it is resilient. Read on and learn how to grow and care for Agastache in your garden. 

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Agastache Ultimate Growing and Care Guide

What is Agastache? 

What is Agastache?

Agastache is a herbaceous perennial, with bountiful flower spikes, and sweet, liquorice scented foliage. Agastache are one of the most decorative members of the Lamiaceae, or mint family with two main sub-species: Korean Mint (Agastache Rugosa) and Anise Hyssop (Agastache Foeniculum).

It is important to note that Anise Hyssop are not Hyssops. The differences are minimal, and growing guides for each are interchangeable. However,

Agastache tend to have tighter flower clusters along their spikes, and while hyssop have a mild mint flavour, Agastache have a unique anise tone to their leaves.

Best Agastache Varieties for the Garden

Agastache Black Adder

Agastache Black Adder can reach 1m tall in their first year, and like all other Agastache won’t push its way around the garden

Blackadder is one of the most reliable tall Anise Hyssops. We grow it as much for its dark brown, almost black seed heads in winter as we do for the flowers.

The flower spikes can reach 1m tall in their first year, and like all other Agastache won’t push its way around the garden. An incredibly striking low maintenance addition to any border.

Agastache Alabaster

Agastache Alabaster prefers slightly drier conditions, and puts up with a lot of competition

Source: Gardenia.net

Alabaster pairs excellently with white lavender or Aquilegia Lime Sorbet. All three share similar flowering months, so for the basis of a white garden, they will be a reliable combination of annuals and perennials.

I find it prefers slightly drier conditions, and puts up with a lot of competition.

Agastache Navajo Sunset

Agastache Navajo Sunset is an outstanding variety, with bright orange flowers, and like its cousins is entirely edible

Source: Morningsunherbfarm.com

I’ve not given advice on Agastache Aurantiaca in this article, as in every way, it shares the same exact care advice as Anise Hyssop. Aurantiaca are better known as Giant Hyssop, and can reach up to 1.2m tall.

Because of their height, they do benefit from staking, but don’t need it if they’re grown away from strong winds. Navajo sunset is an outstanding variety, with bright orange flowers, and like its cousins is entirely edible.

Agastache Rugosa Kolibri

Agastache Rugosa Kolibri is one of those brilliant russet flowered rarities that are always difficult to find in cooler climates

Source: Promessedefleurs.com

By far my favourite Korean Mint. I’ve never tried it for culinary use, but it's one of those brilliant russet flowered rarities that are always difficult to find in cooler climates.

The flowers change from russet, through to salmon, through the pale orange through the season, so you’ll always have something different to look at.

Agastache Little Adder

Agastache Little Adder is a reliable, hardy perennial, only growing to 13cm tall

By far the most common Agastache in garden centres, Little Adder is a reliable, hardy perennial, only growing to 13cm tall. It’s dark purple flowers make a great addition to ornamental pot combinations, whether you’re looking for clashing colours, or variations on blues and purples.

Agastache Growing Habits

Agastache are excellent ground cover perennials, growing in compact clumps and reaching a maximum spread of 50cm. They are either grown as a herb for harvest, or a border perennial.

Agastache make a brilliant addition to mixed borders, and are perfect placed at the front a border for some drama during their long flowering season.

All varieties of Agastache will reliably flower all summer, with some varieties holding their colour right through to mid-autumn.

We grow Agastache Black Adder, a dark blue flowering anise hyssop, which even in our cold corner of the world (Zone 9a) will hold its petals through to mid-autumn, with almost no maintenance needed.

For gardeners on a budget, they are also incredibly simple to propagate from seed, giving you at least 40 new plants per packet, with a very reliable germination rate.

Once you’ve grown them, within three years you can propagate more plants by simply splitting portions of Agastache and lifting them into new positions.

Agastache are very easy to care for, but there are small variations in the needs of Anise Hyssop and Korean Mint:

Agastache Growing Habits

Korean Mint (Agastache Rugosa)

Agastache Rugosa (common names: Korean Mint or Giant Wrinkled Hyssop) is a long-lived perennial, native to East Asia. When plants reach maturity and begin to outgrow their space, they are best propagated through division. 

Korean Mint Size: 

Height

Spread

Time of Maturity

0.5-1m

0.5m

3 years

Korean Mint Conditions:

Soil

Sun

Hardiness

Water

Chalk, loam, clay or sand soils, enriched with compost or manure

Tolerates part shade

Prefers full sun

H5-H6 (-20C)

Drought tolerant. Avoid over watering.

Anise Hyssop (Agastache Foeniculum)

Agastache Foeniculum (common names: Anise Hyssop, Giant Hyssop) is native to upland prairies in North America. In almost all ways its growing habits are identical to its Korean cousin.

However, it is far less tolerant of clay soils. It can be grown in part shade, but prefers full sun, loves moisture, and doesn’t mind wind.

Anise Hyssop Size:

Height

Spread

Time of Maturity

0.5-1m

0.5m

3 years

Anise Hyssop Conditions:

Soil

Sun

Hardiness

Water

Chalk, loam or sand soils, enriched with compost

Tolerates part shade

Prefers full sun

H3 (-5C)

Drought tolerant, well drained soil. Avoid over watering.

Agastache Special Features (Fruits, Flowers, Uses) 

We grew Agastache as a purely ornamental plant for three years before realising they had culinary uses. At a BBQ a few years ago, we picked the leaves from our garden and added them to a salad.

We’ve grown them in the herb garden ever since for their delicate liquorice flavour which is a mind-bending addition to an autumn salad when most of your summer lettuces have ended their season.

Both the leaves and flowers of Agastache are packed with polyphenol antioxidants which, amongst other health benefits, could help protect against cancers, coronary heart disease and joint inflammation.

Agastache rugosa (Korean Mint) has been used for centuries as a herbal remedy across Asia for patients with fevers, indigestion and colds.

But a word of warning; all parts of the plant should be avoided if pregnant or epileptic, as it contains high concentrations of pinocamphone, which can cause over stimulation of the nervous system.

The most common culinary use for Agastache is to dry the leaves and flower spikes for use as a sugar free sweetener, which as well as it’s medicinal benefits, helps to reduce sugar intake in your diet – and is particularly nice as an addition to herbal teas.

How to Grow Agastache

How to Grow Agastache

Propagating Agastache

There are two truly reliable ways of propagating Agastache; seed and division. It is possible to take cuttings, but their aversion to over watering makes them a little more temperamental than your average cutting.

Growing Agastache from Seed

To grow Agastache from seed you will need a seed tray or 9cm pots. If you have saved seeds from existing plants use a seed tray, as germination is likely to be less successful than bought packets.

For seeds from packets, cut out the first few steps, and sow directly into 9cm pots.

  1. Fill a seed tray with seed compost, or sieved garden compost.
  2. Sow sparsely in rows on the soil surface and press in gently. Do not cover.
  3. Water from the base.
  4. Keep in full sun, anywhere temperatures are above 15C.
  5. Water from the base to avoid disturbing the seed while they germinate.
  6. Germination usually takes 2-4 weeks, but can be erratic up to 90 days. 
  7. As soon as seedlings are big enough to handle (2-3 inches), prick out individual plants into 9cm pots, and keep watered until roots appear (4-6 weeks).
  8. When roots appear at the base of the pot, plant your new Agastache in the border, or as part of pot displays.

Sow Agastache any time from early-spring to early-summer, but earlier sowings will give you a full flowering season the same year.

How and When to Divide Agastache

If you have access to mature Agastache plants, division is by far the most reliable way to propagate new clumps. As long as the main clump of Agastache is over 30cm across, it's safe to split it, and you’ll at least double your stock.

If your Agastache is in the border, simply dig up half a clump in early spring, divide as many times as you can. In my experience, splitting into 20-30cm clumps is pretty safe.

Anything less and the divisions may not have enough roots to get going again. If you’ve been growing Anise Hyssops or Korean Mint in pots, simply lift them out and cut through the root ball with a spade.

To plant them back out, just take your new divisions and put them in their new spot, mixing a healthy amount of compost into the planting hole.

Planting Agastache

Planting Agastache

Whether you’ve bought your Agastache in a local garden centre, or you’ve propagated your own, the best time to plant out is late spring/early summer when the weather is reliably mild, and there’s enough regular rain to keep it watered.

That way, you’ll be rewarded with masses of flowers right through summer, and into the autumn. Remember earlier, when I said Agastache wasn’t fussy?

I really wasn’t lying. As long as you keep Agastache away from clay soils, and don’t over-water them, you can place them anywhere other than full shade.

They make great companions to Mediterranean planting schemes, but will fit equally well into a cottage garden, as they don’t mind competition from other plants, since their rhizomes will hold their own without spreading.

I would always advise anyone planning their planting schemes to avoid formal ‘styles’, so think outside the box, and make your garden unique to you. Hyssop and Agastache are brilliant plants to bring out the best in others. 

We keep Agastache Foeniculum Blackadder alongside Heuchera Black Pearl to bring out the colours of each, and a few feet away, have a combination of white lavender and Agastache Rugosa Alabaster to highlight the varied flower spikes.

For Asian varieties, like Korean Mint (Agastache Rugosa) make sure the planting hole is dug out at least twice the size of the root ball, to allow space to spread, and dig through rotted manure, or leaf mould to ensure it has the nutrients to see it through its first few years.

For Anise Hyssop (Agastache Foeniculum), plant exactly as you would with Korean Mint, but avoid manure and stick to well drained materials like leaf mould or mixed garden compost.

Keep the soil surface level with the level of the pot, and plant at least 30cm apart from each other.

Agastache Care Guide

Agastache Care Guide

Anise Hyssop and Korean Mint are incredibly tough plants, if you forget to mulch them, they will forgive you, but mulching once every 2-3 years to improve the soil will give them a noticeable boost.

As a rule of thumb for anything in the border, garden compost is always the best way to mulch. You’ll save money, and won’t need to worry about drainage being affected or weeds, unlike manure.

Here is our review on the best compost tumblers to make garden composting easier. The only guidance that is truly important to care for established Agastache, is to steer clear of chemical fertilizers.

As an edible plant, sticking to organic fertilizers or using compost, manure or chicken manure is the only way to ensure you keep organic crops that are safe to put on your plate.

If you do plan on harvesting the leaves and stems, keeping them watered once every few weeks will give you bigger crisper leaves for salads, but won’t make any difference to the strength of the drought tolerant plant.

While you might be tempted to cut back flower spikes and leaves to neaten up borders in winter, it is much better to leave them in place, as the top growth will die back and feed the roots through winter.

The flower spikes will drop off when new growth comes through in spring. If you do prune the flower spikes back, don’t let them go to waste, dry them out and keep them to flavour drinks.

How to Harvest Agastache

How to Harvest Agastache

All kinds of Agastache can be used as a perennial salad crop, and harvested throughout summer and autumn. Last year’s growth dies back and is replaced by new liquorice flavoured leaves, which you can pick repeatedly from early-summer, right through to the autumn.

To harvest the flower spikes for culinary or herbal benefits, cut them while they are in full flower, then hang somewhere dry until they have lost all their water.

Then simply cut up and stick in an airtight jar. They’ll keep all through winter and add flavour to drinks or baking as a unique sugar substitute.

If you’re not interested in growing for food, but want to keep your table stocked with fresh flowers, cut flower spikes just before they are fully open and put them directly into water. They will continue to open up in a vase, giving you longer to enjoy them.

Common Agastache Pests & Diseases

Agastache and hyssop only have two real predators; slugs and deer. Avoiding these pests is pretty simple, and will also help stave off potential root rot.

Make sure they are planted with good drainage and don’t over-water them. Slugs adore over-watered Agastache, and it’s a sure-fire way to cause root-rot.

If you’re worried about root-rot in Agastache, or have particularly heavy clay soil, there are two options. First, plant Agastache in pots, so you can create the perfect soil mix.

Second, add a layer of grit to the bottom of the planting hole if planting Agastache directly in clay soil. Watch out for leaf spots, leaf rust, or powdery mildew on Anise Hyssops in particular, as this is a sign of overwatering.

Check out our guide on using potassium bicarbonate to get rid and prevent powdery mildew from invading your plants again. 

Agastache FAQ

Is Agastache hardy?

Yes, Agastache Foeniculum is hardy down to -20C, and Agastache Rugosa down to -5C.

How do you care for Agastache?

Agastache prefers full sun, but will tolerate light shade. Plant In well drained compost, and avoid over watering. Mulch every 2-3 years.

How quickly does Agastache grow?

Agastache grows from seed to a spread of 0.5m in maturity within 3-4 years.

How quickly does Agastache germinate?

Agastache has erratic germination rates, but will usually germinate within 14-28 days. It can take up to 90 days for seedlings to appear.

Is Agastache invasive?

No, unlike other members of the Lamiaceae family, Agastache will keep itself contained, and rarely spreads from rhizomes.

Does Agastache come back every year?

Yes, Agastache is a hardy perennial. Some varieties of Korean Mint benefit from mulching in winter to protect from severe frost.

Should I cut back Agastache?

No, Agastache will die back and feed its roots over winter, which helps with a brighter display the following year.

Can I grow Agastache in pots?

Yes, and they will thrive with the improved drainage above ground.

Is Agastache good for wildlife?

Agastache is brilliant for pollinators. Bees, butterflies and pollinating wasps love the scented, nectar rich flowers.

Wrapping Up Our Agastache Guide

Agastache are a worthy addition to any planting scheme, making the most of small spaces, and easy to add into existing planting schemes. They are easy to care for, and make excellent intuitive plants for newcomers to the world of horticulture.

Their health and nutritional benefits, as well as their flavour is worth giving up garden space for in itself, and knowing how beautiful they can be should be more than enough to convince you.

There are so many Agastache varieties to choose from, but I’m a sucker for Anise Hyssop.

About the Author Mabel Vasquez

Mabel has enjoyed a long career as a horticulturist, working in nurseries and greenhouses for many years. Although she loves all plants, Mabel has developed a particular passion over the years for herb gardens and indoor plants. Mabel has since retired from her horticulture career and loves sharing her many years of experience with our audience here at Sumo Gardener.

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