Mature size & growth rate

How big does King George aster (Aster amellus 'King George') get?

Also called King George aster, King George Italian aster.

More about king george aster

About King George aster

Aster amellus 'King George' · also called King George aster, King George Italian aster · flowering

'King George' is a long-established cultivar of Italian aster, prized for its large, rich violet-blue daisy flowers with deep golden-yellow disc centres produced freely from late August through September. It is compact, reliably mildew-resistant, and thrives in alkaline, well-drained soils. An AGM-awarded plant from the Royal Horticultural Society, it is one of the finest selections of A. amellus for late-season colour.

Mature size: 50–60 cm tall and 30–40 cm wide (20–24 in tall, 12–16 in wide)

Indoor size vs how big it gets in the wild

King George aster stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward. Indoors and in a pot, expect 50–60 cm tall and 30–40 cm wide (20–24 in tall, 12–16 in wide). A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Growth rate and years to mature

King George aster is a moderate grower. Realistically, expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Its feeding profile backs this up: one application of balanced granular fertiliser in early spring is sufficient. avoid high-nitrogen or rich compost mulches — they encourage vegetative growth at the expense of flowers and plant longevity.

Want this turned into the right next pot at the right moment? The pot size calculator and the king george aster repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast king george aster grows.

How to keep king george aster smaller

You are not stuck with the maximum size. For king george aster specifically, these are the levers, in order of impact:

Divide the clump every year or two — splitting king george aster is the main way to control its spread and refresh it.
Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump.
Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

The keep-it-smaller method, step by step

Lift the whole plant. Slide king george aster out of its pot in spring when the clump has filled it.
Split the clump. Tease or cut the rootball into two or more sections, each with healthy roots and growth.
Repot one division. Put a single division back in the original pot to reset it to a smaller size; pot or give away the rest.
Remove offsets as they form. Through the year, detach new runners or pups to stop it spreading again.

How to grow king george aster bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for king george aster the accelerators are:

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger.
Good light plus regular feeding maximises offset and runner production.
Leave plantlets and offsets attached and feed through the growing season for the fastest spread.

Light is almost always the ceiling. The king george aster light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When king george aster outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for king george aster:

The clump bulging over the pot rim or splitting the pot — the cue to divide, not to find a bigger room.
A dense centre that goes bare or tired while the edges keep spreading.
Runners or offsets escaping across the shelf or into neighbouring pots.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the king george aster repotting guide. If you want more of this plant instead of a bigger one, the king george aster propagation guide turns prunings into new plants.

King George aster size — frequently asked questions

How big does king george aster get?

King George aster reaches 50–60 cm tall and 30–40 cm wide (20–24 in tall, 12–16 in wide) when grown indoors. Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Is king george aster slow or fast growing?

King George aster is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. King George aster stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward.

How long does king george aster take to reach full size?

Roughly three to six years to reach mature indoor size, gaining a steady amount each growing season. Light, pot size and feeding move that timeline more than anything else.

How do I keep king george aster smaller?

Divide the clump every year or two — splitting king george aster is the main way to control its spread and refresh it. Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump. Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

How can I make king george aster grow bigger or faster?

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger. Good light plus regular feeding maximises offset and runner production. Leave plantlets and offsets attached and feed through the growing season for the fastest spread.