Repotting guide

When & how to repot Prince's feather (Amaranthus hypochondriacus)

Also called Prince's feather, grain amaranth, purple amaranth, prince-of-wales feather.

More about prince's feather

About Prince's feather

Amaranthus hypochondriacus · also called Prince's feather, grain amaranth · flowering

Prince's feather is a tall, imposing warm-season annual bearing erect, bristling plumes of deep maroon-red to purple flowers on strong stems above large burgundy-flushed leaves. Also grown as a grain crop, its seeds are a nutritious pseudo-grain rich in protein. It thrives in full sun, heat and well-drained soil. Apply genus-level caution for pets, as Amaranthus retroflexus is ASPCA-listed as toxic.

Mature size: 120-180 cm tall, 45-60 cm spread

Watch for — Cercospora leaf spot: Circular tan spots with purple margins caused by Cercospora fungi can develop in warm, wet summers — improve plant spacing for airflow, avoid overhead watering and remove affected leaves promptly.

How to tell prince's feather needs repotting

Repotting on a calendar is less reliable than reading the plant. For prince's feather, watch for these signs:

Roots circling the bottom of the module or pot, or poking out of the drainage holes.
The seedling dries out within a day and growth has visibly stalled.
Roots are white and matted in a tight spiral when you tip the plant out.
It has outgrown its current container for the stage of the season — pot prince's feather on before it becomes hard root-bound.

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 prince's feather

Pot on seedlings as they grow; not a perennial repot. Prince's featheris grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Tall, erect, fast-growing warm-season annual with upright plume-like flower spikes.

What size pot to step prince's feather up to

Pot prince's feather on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

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 prince's feather

Pot prince's feather on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting prince's feather

Pot on before it is root-bound. Check prince's feather regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
Pot into rich mix. Set it into fresh moderately fertile to lean, well-drained loam or sandy loam at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water prince's feather in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for prince's feather

Prince's feather wants moderately fertile to lean, well-drained loam or sandy loam. Grows well in moderately fertile, well-drained soil with a neutral pH (6.0-7.0). As with other grain amaranths, it tolerates poorer soils than most annuals, but benefits from some organic matter for best stem height and plume size. Heavy, wet soil is poorly tolerated; raised beds or light loam are ideal. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting prince's feather — frequently asked questions

How often should you repot prince's feather?

Pot on seedlings as they grow; not a perennial repot for prince's feather. Prince's feather is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into moderately fertile to lean, well-drained loam or sandy loam so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does prince's feather need?

When is the best time of year to repot prince's feather?

Can you put prince's feather straight into a much bigger pot?

No. Even a fast-growing prince's feather should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise prince's feather after repotting?

Not immediately. Wait about 1 week after repotting prince's feather. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.