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Chatham Islands Poa

Poa chathamica

At Risk - Naturally Uncommon

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Chatham Islands poa (Poa chathamica), also called bog poa, is a perennial grass found nowhere else but the Chatham Islands, where it grows on all the main islands. It is variable in form: on dunes and in bogs it creeps by long narrow rhizomes to make dense drooping swards, while on rock it forms stiffly erect tufts up to about 1 m tall. Its leaves range from light green to blue-green and are tough and ribbed. It is ranked At Risk - Naturally Uncommon because of its small island range, and it is affected by grazing and by invasive marram grass on the dunes. Explore more native grasses and flaxes in our native plant guide.

Chatham Islands Poa (Poa chathamica) in its natural habitat
Image credit: Chatham Islands Poa (Poa chathamica) - photo by Wikipedia contributors, via Wikipedia

Plant Description

Poa chathamica is a light green, dark green or blue-green perennial grass. Depending on its situation it either creeps widely by long, narrow rhizomes to build dense, leafy, drooping swards, or grows as stiffly erect tufts up to about 1 m tall. The leaf blades are long and narrow, roughly 5 to 60 cm long and 2.5 to 4.5 mm wide, folded or inrolled, tough and leathery in texture, with a ridged upper surface carrying short prickle-teeth and thickened margins.

The flowering stems reach 10 to 80 cm and are densely rough just below the head. The panicle is 5.5 to 12 cm long with spreading or erect branches, carrying large spikelets 6.5 to 14.5 mm long, each with 2 to 5 florets, greyish green to light greenish brown in colour.

Its closest relatives are Poa anceps, P. xenica and hexaploid forms of P. cita. NZPCN notes that it differs from P. anceps in its ribbed leaf blade surfaces and in its high chromosome number (2n = 112). On the Chathams, its combination of rhizomatous spread, tough ribbed leaves and large spikelets helps separate it from other grasses.

Quick Facts

Poa chathamica quick facts
Scientific Name Poa chathamica
Height Swards low and drooping; tufts up to about 1 m
Spread Spreads widely by long narrow rhizomes
Water Needs Tolerant of both damp peat bogs and free-draining dunes
Light Full sun
Frost Tolerance Moderate; suited to the cool, mild oceanic Chatham climate
Salt Tolerance High; grows on coastal dunes and sea cliffs
Growth Rate Moderate; spreads steadily by rhizomes
Lifespan Perennial

Climate Best Suited to

It suits the cool, windy, humid oceanic climate of the Chatham Islands, where frosts are light and salt-laden wind is constant. Mainland gardens with mild winters and plenty of sun and wind are the closest match.

Regional Suitability

City suitability for Poa chathamica
City Climate Suitability
Auckland Medium
Wellington High
Christchurch Medium
Dunedin High

Plant Habitat

Poa chathamica is endemic to the Chatham Islands and is found on all the main islands of the group. It grows both near the coast and inland.

It is unusually broad in its habitat choices for a narrow-range endemic. NZPCN records it as widespread on sand dunes, within restiad peat bogs, in rough pasture, along stream banks and in river gorges, and on rock outcrops, cliff faces and boulder falls.

Growing Requirements

Soil Requirements

In the wild it grows on both sand and peat, so it is not fussy about soil type as long as it has an open, sunny position.

  • Sandy, free-draining soils suit the sward-forming dune form
  • Peaty, damp soils are also tolerated
  • Avoid rich garden soil, which encourages weeds that crowd it out

Light Requirements

NZPCN advises full sun, which matches its open dune, bog and cliff habitats.

  • Plant in full sun
  • Avoid shade from trees or tall shrubs

Water Requirements

It copes with conditions from wet peat bog to dry dune sand. In cultivation, regular moisture while establishing is enough.

  • Water new plantings until rhizomes are established
  • Established plants handle short dry spells
  • Its wetland indicator status is facultative, meaning it occurs in wet and dry places

Planting and Establishing

Plant rooted pieces or seedlings in spring in an open, sunny site. Because it spreads by rhizomes, give it room to form a sward, or contain it where it should stay in one place.

On the Chatham Islands, plants for restoration should be grown from local seed or divisions. Mainland gardeners are unlikely to find it for sale, as NZPCN lists it as not commercially available.

Ecological Role

On Chatham dunes it is one of the native sand-binding grasses, helping to stabilise loose sand. Its spread there is limited by competition from introduced marram grass, which displaces native dune vegetation.

Like other Poa species it is wind pollinated. Its seeds and foliage support native insects, although no specific associations for this species are documented in the sources consulted.

Uses & Significance

Garden Uses

It is a tough grass for exposed coastal gardens and for Chatham Islands restoration plantings.

  • Dune and coastal restoration on the Chathams
  • Groundcover sward on banks
  • Specimen tufts among rocks in a coastal garden

Ecological Value

As a Chatham endemic, it is part of the distinctive native plant cover of the islands.

  • Binds sand and stabilises banks
  • Forms native cover in peat bogs and on cliffs
  • Represents a range-restricted island lineage

Landscaping Uses

Use the rhizomatous form to cover a sunny bank or sandy slope, where its drooping leaves make a soft blue-green sward. Tufted plants from rocky sites can be planted singly as accents in a gravel or coastal garden.

Pair it with other Chatham Islands plants such as Chatham Island forget-me-not where those are grown, or with mainland coastal natives for a hardy seaside planting.

Seasonal Care Calendar

Spring

Flowering begins in September, and new rhizome growth starts.

  • Plant out rooted pieces
  • Remove competing weeds

Summer

Flowering continues to January and seed ripens from January to February.

  • Collect fresh seed
  • Water new plants in dry spells

Autumn

Growth slows; a good time to sow fresh seed collected in summer.

  • Sow seed
  • Tidy dead flower stems

Winter

Plants stay green in the mild Chatham winter but grow little.

  • Little care needed
  • Check for weeds invading swards

When to Prune and How Much

No regular pruning is needed. Old flowering stems and dead leaves can be combed out by hand to keep tufts tidy.

If a sward spreads beyond where it is wanted, cut out the rhizomes with a spade and use the pieces to start new plants.

How to Grow Chatham Islands Poa

NZPCN reports that Poa chathamica is easily grown from fresh seed and from rooted pieces, so it is one of the more straightforward Chatham grasses to propagate. The catch is that cultivated plants rarely flower, so seed usually has to come from wild plants, collected with permission and in small amounts. Division of rhizomatous plants is therefore the most reliable method in a nursery.

From Seed

Seed ripens in January and February, a month or so after flowering ends. Use fresh seed for the best germination, since NZPCN specifically recommends fresh seed.

  1. Collect ripe seed heads in late summer when the spikelets turn straw coloured
  2. Rub out the seed and sow it fresh on a free-draining seed mix
  3. Cover lightly with fine grit and keep evenly moist in a sunny spot
  4. Prick out seedlings into individual pots once they have several leaves
  5. Grow on for a season before planting out

By Division of Rhizomes

Because it spreads by long, narrow rhizomes, rooted pieces can be lifted from the edge of an established sward. Divisions establish quickly and are the easiest way to multiply plants that do not flower in cultivation.

  1. In spring, dig a clump with a length of rhizome and several shoots
  2. Trim the leaves back by half to reduce water loss
  3. Pot into a sandy mix or plant directly into prepared ground
  4. Keep moist and in full sun until new shoots appear
  5. Plant out once the division has rooted firmly, giving it space to spread

Pests & Diseases

No specific insect pests or diseases are recorded for this species. Its main problems are grazing by stock and smothering by aggressive introduced grasses.

In gardens, keep it free of couch and other running weeds, which are hard to separate from its own rhizomes once they mingle.

Cultural Significance

No Moriori or Māori name or traditional use is recorded for Poa chathamica in the sources consulted.

It was described by Donald Petrie, the Otago botanist who named many New Zealand grasses. Its epithet chathamica simply means from the Chatham Islands.

Bonus Tip

If your plant never flowers, do not assume it is unhealthy. NZPCN notes that Poa chathamica rarely flowers in cultivation, so propagate it by dividing rhizome pieces instead of waiting for seed.

Plant Conservation

Poa chathamica is ranked At Risk - Naturally Uncommon (2023) with the qualifiers Island Endemic and Range Restricted. It has held a Naturally Uncommon ranking in every assessment since 2009.

NZPCN identifies habitat modification, stock grazing and competition from introduced plants such as marram grass as threats. Fencing out stock, controlling marram on dunes and restoring peatland help secure its habitat.

Frequently Asked Questions

Where does Chatham Islands poa grow?

It is endemic to the Chatham Islands and occurs on all the main islands, from coastal sand dunes and restiad peat bogs to stream banks, river gorges, rock outcrops, cliff faces and boulder falls.

Is Poa chathamica the same as bog poa?

Yes. NZPCN calls it Chatham Islands poa, while the Flora of New Zealand factsheet lists bog poa as its common name. Both names refer to Poa chathamica.

Why is Chatham Islands poa At Risk?

It is classed as Naturally Uncommon because it is confined to one island group. NZPCN lists habitat modification, stock grazing and competition from introduced plants such as marram grass as threats.

Can you grow Poa chathamica from seed?

NZPCN says it is easily grown from fresh seed and from rooted pieces and does best in full sun, although cultivated plants rarely flower.

Sources and Further Reading

The botanical, growing, and conservation details for Chatham Islands Poa (Poa chathamica) on this page draw on the New Zealand plant references below. Consult them for full technical records and the latest distribution data.