Northern sea oats
Chasmanthium latifolium
also called river oats, wild oats
The one ornamental grass that is genuinely good in shade, hung with flat oat-like seed heads that turn bronze and rattle in the wind all winter.
Spacing & sowing
- Plant spacing
- 23.6 in
- In-row spacing
- 19.7 in
- Between rows
- 2 ft 6 in
- Square-foot density
- Not suited to SFG
- Sow depth
- 0 in
Calendar (from your frost dates)
- Sow indoors
- 42 days before the last spring frost
- Sow direct
- 21 days before the last spring frost
- Plant out
- at the last spring frost
Growing
- Type
- Grass · Perennial
- Botanical family
- Mixed / other
- Sunlight
- Part shade to full sun
- Watering
- Moderate
- Soil
- Average to moist, tolerant of most things
- Feeding
- Gentle all-organic
- USDA zones
- 3a–9b
- Frost tolerant
- Yes
Harvest
- When
- Not harvested for food. Cut the seed heads for drying from late summer, while they are still green or just turning bronze.
- What to look for
- The flat oat-like spikelets are fully formed and hanging. Cut green for the best color in a dried arrangement; leave them longer and they turn a lovely bronze but shatter more.
- How to harvest
- Cut long stems and hang them upside down in small bunches in a dry airy place for a fortnight.
- How often
- One or two cuts in late summer. Cutting is also the seedling control — the plant self-sows heavily.
- Storing the crop
- Dried stems keep for years in a vase out of direct sun. Cut the whole plant to the ground in late winter before the new growth starts.
Pests & problems
- Aphids Small sap-sucking insects — greenfly, blackfly — that cluster on soft new growth and excrete sticky honeydew. Squash by hand, hose off with water, and encourage ladybirds and lacewings.
- Leaf spot Brown or black spots that spread and merge in wet weather, sometimes with yellow halos. Pick off affected leaves, clear fallen ones, and water at the base.
- Rust Orange-brown powdery pustules on leaf undersides, weakening the plant over the season. Remove affected leaves, avoid overhead watering, and clear all debris in autumn.
Garden allies
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Aphid midge Aphidoletes aphidimyzaHunts Aphids
A tiny midge whose orange maggots paralyze aphids and drink them dry, twenty or more each. Sold as a greenhouse biological control and resident outdoors wherever there are small nectar flowers and an unsprayed aphid colony to find.
- Assassin bug ReduviidaeHunts Aphids
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Big-eyed bug Geocoris spp.Hunts Aphids
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Aphids
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Dragonflies & damselflies OdonataHunts Aphids
Aerial hunters that take mosquitoes, midges and small flies on the wing all day, and whose larvae spend a year or more clearing the same insects from the water. A pond with planted margins and no fish is the way to have them.
- Garden birds PasseriformesHunts Aphids
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Green lacewing Chrysoperla carneaHunts Aphids
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Hoverfly SyrphidaeHunts Aphids
Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them.
- Ladybird (lady beetle) CoccinellidaeHunts Aphids
The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working.
- Minute pirate bug Orius spp.Hunts Aphids
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Parasitic wasps Braconidae & TrichogrammaHunts Aphids
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Praying mantis MantidaeHunts Aphids
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Soldier beetle CantharidaeHunts Aphids
Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds.
- Spiders AraneaeHunts Aphids
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
Did you know?
It seeds about generously — cut the heads for the vase in September and you get the arrangement and the seedling control in one go.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com