Repotting guide

When & how to repot Agapanthus 'Navy Blue' (Agapanthus 'Navy Blue')

Also called Navy Blue agapanthus, dark blue lily-of-the-Nile.

More about agapanthus 'navy blue'

About Agapanthus 'Navy Blue'

Agapanthus 'Navy Blue' · also called Navy Blue agapanthus, dark blue lily-of-the-Nile · flowering

Agapanthus 'Navy Blue', often sold as 'Midnight Star', is a compact deciduous cultivar prized for its deep, almost violet-blue trumpet flowers in dense rounded umbels through mid to late summer. Its shorter stature suits containers and small borders. Like other hardy agapanthus it flowers most freely in full sun and sharp drainage with congested roots.

Mature size: 60-80 cm tall in flower and around 45 cm wide, more restrained than tall border types and ideal for pots.

Watch for — Sparse flowering: Too much shade, excess nitrogen, or a freshly divided clump. Move to full sun, use high-potash feed, and let the roots become slightly congested before expecting heavy bloom.

How to tell agapanthus 'navy blue' needs repotting

Repotting on a calendar is less reliable than reading the plant. For agapanthus 'navy blue', watch for these signs:

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for agapanthus 'navy blue') flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to repot.

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 agapanthus 'navy blue'

Only every 2–4 years, when genuinely crowded. Agapanthus 'Navy Blue' is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Compact, clump-forming herbaceous perennial with neat strap-like deciduous leaves and upright scapes carrying tight, near-spherical flower heads..

What size pot to step agapanthus 'navy blue' up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Agapanthus 'Navy Blue' positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping agapanthus 'navy blue' into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

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 agapanthus 'navy blue'

Early spring, just as new growth restarts, is the ideal window for agapanthus 'navy blue'. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting agapanthus 'navy blue'

Confirm it actually needs it. Slide agapanthus 'navy blue' out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip agapanthus 'navy blue' out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh free-draining fertile loam, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water agapanthus 'navy blue' again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for agapanthus 'navy blue'

Agapanthus 'Navy Blue' wants free-draining fertile loam. Likes a rich but sharply drained soil; add grit on clay. Excellent in pots in loam-based John Innes No. 3 with extra grit, where slight root restriction actually boosts flowering. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting agapanthus 'navy blue' — frequently asked questions

How often should you repot agapanthus 'navy blue'?

Only every 2–4 years, when genuinely crowded for agapanthus 'navy blue'. Only repot agapanthus 'navy blue' every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using free-draining fertile loam. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does agapanthus 'navy blue' need?

When is the best time of year to repot agapanthus 'navy blue'?

Does agapanthus 'navy blue' like to be root-bound?

Yes — agapanthus 'navy blue' genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise agapanthus 'navy blue' after repotting?

Not immediately. Wait about 4 weeks after repotting agapanthus 'navy blue'. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.