Repotting guide

When & how to repot Agastache 'Black Adder' (Agastache 'Black Adder')

Also called Black Adder agastache.

More about agastache 'black adder'

About Agastache 'Black Adder'

Agastache 'Black Adder' · also called Black Adder agastache · flowering

Agastache 'Black Adder' is an aromatic hybrid hyssop with dense, smoky violet-blue flower spikes emerging from near-black buds from midsummer to autumn. Vigorous and long-blooming, it wants full sun and free-draining soil, tolerates heat and drought once established, and is a prolific nectar source for bees, butterflies and hummingbirds.

Mature size: About 60-90 cm tall and 45-60 cm wide (2-3 ft by 1.5-2 ft).

How to tell agastache 'black adder' needs repotting

Repotting on a calendar is less reliable than reading the plant. For agastache 'black adder', watch for these signs:

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot agastache 'black adder'

Every 2–3 years, into bone-dry mix. Agastache 'Black Adder''s growth habit — upright, bushy, clump-forming aromatic perennial (a foeniculum-type hybrid) with mint-family foliage and dense, branching flower spikes over a very long season. — sets the pace. Agastache 'Black Adder' is an aromatic hybrid hyssop with dense, smoky violet-blue flower spikes emerging from near-black buds from midsummer to autumn. Vigorous and long-blooming, it wants full sun and free-draining soil, tolerates heat and drought once established, and is a prolific nectar source for bees, butterflies and hummingbirds.

What size pot to step agastache 'black adder' up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Agastache 'Black Adder' stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot agastache 'black adder'

Spring or summer, while agastache 'black adder' is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting agastache 'black adder'

Repot dry. Do not water agastache 'black adder' for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty well-drained, moderately fertile soil ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set agastache 'black adder' at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep agastache 'black adder' completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for agastache 'black adder'

Agastache 'Black Adder' wants well-drained, moderately fertile soil. Light, free-draining loam or gritty soil is ideal; it dislikes heavy, wet clay. Sharp drainage, especially in winter, is more important than fertility. Neutral pH around 6.5-7.5 suits it. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting agastache 'black adder' — frequently asked questions

How often should you repot agastache 'black adder'?

Every 2–3 years, into bone-dry mix for agastache 'black adder'. Repot agastache 'black adder' every 2–3 years into a snug pot of well-drained, moderately fertile soil, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does agastache 'black adder' need?

When is the best time of year to repot agastache 'black adder'?

Should you water agastache 'black adder' after repotting?

No — not straight away. Repot agastache 'black adder' into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise agastache 'black adder' after repotting?

Not immediately. Wait about 3 weeks after repotting agastache 'black adder'. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.