Grow purpletop in full sun to part shade, on soil that dries between waterings. Grease grass is the same plant. It is not purple lovegrass.
Give it full sun to part shade and soil that dries between waterings
| Factor | Recommended | Avoid |
|---|---|---|
| Light | Full sun to part shade | Do not bury it in deep shade that stops the purple panicle |
| Water | Water to settle a new plant, then let the bed dry between waterings | Do not keep the bed wet after it is established |
| Soil | Average even infertile ground that drains — clay, loam, sand, or shallow rocky soil | Do not plant it in a boggy pocket |
| Size | About 3 to 5 feet tall and 1 to 3 feet wide | Do not crowd it into a tight pocket |
| Salt | It handles roadside salt | Do not keep the bed wet just because the site is a roadside |
| Winter | Leave the standing clump for cover and seed, then cut in late winter | Do not shear new green blades in spring |
Purpletop is Tridens flavus, a warm-season bunchgrass with an open, drooping panicle of reddish-purple spikelets in late summer. Give it full sun to part shade and ground that drains, because a wet pocket after establishment is the primary cause of a thin or rotting clump [1].
Part shade is fine along a woodland edge. Deep shade is not, because the panicle thins and the clump leans. Medium to moderately dry soil is enough once the roots take [2]. Water to settle a new plug, then let the bed dry between waterings. Extra water in a long dry spell can keep the blades green, but do not keep the bed wet in summer heat [3].
The purple haze is the flower panicle, held on branches that droop at the tips. The stems and spikelets carry a thin oil, so a hand run up the seed head comes away greasy — that is why shops also call it grease grass.
Does purpletop need full sun?
Full sun makes the strongest panicle. Part shade along a woodland edge still works. Deep shade thins the clump and cuts the purple show.
How often should I water purpletop?
Water to settle a new plant, then let the bed dry between waterings. Do not keep the bed wet after it is established.
Plant in spring, with the crown at soil level
The usual start is a nursery plug after the soil warms in spring, because this is a warm-season grass. You can also set a pot in early fall. Skip midsummer heat. Set the crown at the soil line, and leave about 1 to 3 feet between plants so the second-year clump has room. To raise it from seed, see Growing Purpletop From Seed.
- Set a nursery plug after the soil warms in spring, or in early fall. Do not transplant in summer heat.
- Keep the crown at the soil line, not buried under a mound of mix.
- Space plants about 1 to 3 feet apart, and water once to settle.
- Then let the bed dry between waterings while the roots take.
When do I plant purpletop?
Plant a plug in spring after the soil warms, or in early fall. Avoid midsummer heat. Set the crown at the soil line.
Divide a crowded clump in spring
If the clump is crowded, lift it in spring and split it into sections that each have roots and shoots. Short rhizomes hold the tuft together, so you will cut through that crown. Replant at the same depth and water to settle. Do not wait until summer heat to divide it. Stem cuttings are not the home method.
- Lift the clump in spring before summer heat.
- Split it so each piece has roots and shoots.
- Replant at the soil line and water to settle.
Cut last year's leaves in late winter
Leave the clump standing through fall and early winter. Birds take the seed, and the standing blades give cover. In late winter or very early spring, cut last year's leaves down to a few inches before new blades show. Do not mow the purple panicle in summer if you want the show, and do not shear new green growth.
- Wait until late winter, before new blades show.
- Cut last year's leaves down to a few inches.
- If you do not want seedlings, cut the panicles after they fade instead of leaving every head to drop seed.
When do I cut purpletop back?
In late winter, before new blades show, cut last year's leaves down to a few inches. Leave the clump standing through fall.
Not purple lovegrass — and not redtop
Purple lovegrass is Eragrostis, a low tuft about 1 to 2 feet tall with a denser purple haze and no oil on the panicle — see How to Grow Purple Lovegrass. Redtop is Agrostis gigantea, a smaller grass with red spikelets that bloom earlier in summer. Neither plant leaves oil on your hand. Confirm the Latin on the tag is Tridens flavus [4].
Is this purple lovegrass?
No. Purpletop is Tridens flavus, a 3- to 5-foot clump with an open, drooping panicle. Purple lovegrass is Eragrostis, shorter, denser, and not greasy.
Is this redtop?
Shops sometimes print redtop or tall redtop on a Tridens tag. True redtop is Agrostis gigantea: smaller, with red spikelets that bloom earlier, and no oil on the panicle.
If last year's blades are still standing and new green is pushing, cut the old clump back this week so the fresh leaves are not buried.
FAQ
Is grease grass the same plant?
Yes. Grease grass and greasy grass are shop names for purpletop, from the oil on the seed heads.
Is Chapman's tridens a different plant?
Chapman's tridens is a related species with stiffer panicle branches. This catalog holds Tridens flavus only.
Can I grow purpletop in a pot?
A draining pot can hold a plant through the first season. Let the mix dry between waterings. Open ground that drains is the simpler long-term home.
Does purpletop spread?
It holds as a clump on short rhizomes and can self-sow. Pull seedlings if you do not want extra plants.
Related guides
Recommended plants
References
- [1] NC State Extension Gardener -
https://plants.ces.ncsu.edu/plants/tridens-flavus/ - [2] Illinois Wildflowers -
https://www.illinoiswildflowers.info/grasses/plants/purpletop.htm - [3] Lady Bird Johnson Wildflower Center -
https://www.wildflower.org/plants/result.php?id_plant=TRFL2 - [4] University of Illinois Extension -
https://extension.illinois.edu/grasses/purpletop
This note is part of Tridens Guides.
More first-season notes by plant are gathered in How to Grow Guides.
Updated: Reviewed by Bosquelle Editors