Purpletop Grass (Tridens Flavus)- A Beginners Guide

One of the prettier sights you may encounter in late fall is a field of Purple Top cutting a purple ribbon across the horizon. Seeing the purple blooms of this native grass dance and sway in the wind is a relaxing and almost Zen-like experience. And if you get out hiking, you are likely to encounter this grass if you’re on the Eastern half of America as it frequently grows in pastures, meadows, and along farm fields and roadsides.

Purpletop is a perennial bunchgrass native to Eastern North America. Scientifically known as Tridens flavus, it grows 3-5′ tall in full sun and medium to dry soils. Important to wildlife, it is a hostplant for several butterfly caterpillars and is good forage for livestock. When planted densely, it creates stunning displays in late summer to fall^[1][2][3].

In the right setting, Purpletop will cut a majestic ribbon to split the horizon. But in order to accomplish this it must be a dense planting. When an individual plant is examined up close you can see that while it is pretty, a solo plant doesn’t have that ‘wow’ factor. No, it must have multiple plants with a depth of field to give those rich purple hues.

Now, although this grass is always listed in that it grows 3-5′ tall…that is referring to the overall plant size. You see, the main ‘grassy’ part is really just a clump of arching leaves that is 2′ or less. The upper stalk that rises above this, that contains the ‘purple’ bloom, is not large enough to obstruct your view as it is just a thin stalk/flower. And you’ll need a lot of plants to create a purple ribbon effect.

I have a small cluster/colony of plants growing in our backyard micro-prairie.  I will be adding more plants through direct sowing this fall.  I have them because I like that it helps add cover for wildlife throughout the winter.  And the seeds provide food for birds and other animals. I don’t expect to create the ‘purple ribbon’ effect as I just don’t have the space and am not going to plant densely enough. But if you are looking for a native grass with pink/purple effects, but don’t have a hayfield, then consider Pink Muhly grass instead.

Purpletop Grass Facts

• Native range is from the great plains to the Atlantic Ocean
• Is hardy from zones 3-10.  Check you USDA garden zone here.
• Will grow 5′ tall if unmowed, but the clump is typically 24″
• Purpletop grows well in poor soils, where other plants struggle
• Doesn’t require fertilizer to grow well
• Provides valuable food for birds in winter
• Is drought tolerant
• The Scientific Name of Purpletop Grass is Tridens Flavus

Native Range

The native range of Purple Top grass covers roughly half of North America. From Texas to Nebraska, then East to Florida and up to the border of Maine^[1].

Reference table

Common Name	Purpletop, Purple Top, Grease grass
Scientific name	Tridens flavus
Bloom Time	Late Summer
Bloom Duration	2-3 weeks
Color	Dark Purple
Bloom Size	¼-1/2” spikelets (6-12 mm)
Characteristics	Individual spikelets attached to a small stem that branches from the top.  There are multiple stems per plant.
Height	3-5’ (1-1.5 m)
Spacing/Spread	0.5-3’ (0.3m – 1 m)  Plant more densely for a showier display
Light Requirements	Full Sun / Partial sun
Soil Texture	Clay, Loam
Moisture	Dry to Medium
Maintenance	None.  Cut back in Spring after insects have emerged
Typical Use	Meadow, prairie, roadside, erosion control
Fauna Associations	Caterpillars and other insects feed on foliage
Larval Host	Zabulon Skipper, Crossline Skipper, Homomok Skipper, Little Glassywing, Wood Nymph
Sowing Depth	0-1/8” (0-3 mm)
Stratification	60 days cold stratification.  Or direct sow in Autumn/Winter
Native Range	Eastern North America / USDA Zones 3-10
Notes	Mass plantings look really cool of this grass

Benefits

Beauty

The most obvious benefit of Purpletop grass most people is the beauty shown in large colonies/plantings. Depth is needed to create this effect, but it is gorgeous as well as relaxing to see a large stand swaying in the wind in late summer / early Autumn.

Wildlife

Most people don’t think of grasses as supporting pollinators, but Purpletop does! A surprising fact about Purpletop is that it hosts caterpillars of several skippers and moths^[2][4]. Butterflies/moths only lay their eggs on certain species of plants, and this species of grass directly supports them, as their caterpillars will feed on the leaves.

Forage

Purpletop can/is foraged by livestock and cattle. So it is a welcome site in a hayfield.

Purpletop Physical Description and Identification

When not in bloom it is a fairly plain and unassuming grass, that can easily be confused for other bunchgrass species (at least by me).  But if given space the grass will spread out diametrically, as the stalks seem to grow at an angle and not straight up vertically.

Stalk / Stem

Each plant will have several stalks (culms) emanating from a central root stock.  I’ve observed the stalks growing at approximately a 60-80 degree angle as measured from horizontal, upwards.  The stalks are green.

Leaves

On each stalk there will be multiple blades in an alternate formation along the clump.  The blades or leaves are about 12-14″ long by 1/2″ wide^[3].  The leaves wrap around the stalk, more than 50% of the diameter usually.

Flower

At the top of the stalk there will be panicles of spikelet flowers (that eventually turn purple).  These spikelets are attached to stems that are up to 1′ long^[3].  I think of the overall shape at the top as being similar to a pine tree, in that you have all the spikelets and stems arranged (loosely) in a cone shape.  With the tip of the cone being at the top.

Individual spikelets 1/4″ – 1/2″ long and kind of oblong shaped.  There will generally be 10-20 individual spikelets on each plant.  After blooming, the spikelets will turn to a dull tan/gray color.

Root

Purple Top Grass has fibrous roots.  This helps it hold soil very well and will prevent or reduce erosion.

Purpletop Growing Conditions

This is a great colonizing grass to grow in hot and dry conditions.  Purpletop will grow best in full sun. Several field studies have shown that Purpletop grass produces more mass and sets more seed in full sun and slightly dry conditions^[5].  It is drought tolerant, and prefers dry soil^[6].  It will also grow well in medium moist areas.  Do not plant this in rain gardens or along ponds, streams, etc.

For soil textures, it is highly versatile in that it has no problem growing well in clay or loam. There have been mixed reports in terms of it growing in sandy soils^[7], however I’ve had it growing in my backyard, which has sandy loam for about 6 years now.

How to care  for Purpletop

Almost no care is required for Purpletop as long as it is planted in its preferred growing conditions of full sun and dry to medium-moist soil.  As it is native, there are no real diseases to be concerned about.

Maintenance

There really isn’t any maintenance required for Purple Top. Considering you need a lot of it to get the ‘purple ribbon’ effect, most people are probably going to use this in a meadow or hayfield.

Video Guide

Below is a video I recently made covering all aspects of Purple Top Grass. You should watch it for the photography if nothing else!

How to grow Purpletop from seed

Germination rates of Purpletop grass is relatively low. To increase the germination rate, a cold-moist stratification period of 4-8 weeks should be performed^[6]. For regular backyard gardeners, there are two ways to achieve this – using a moist paper towel in the fridge, or winter sowing the seed. Personally, from my own experience over many years, winter-sowing is easier and more effective with less headaches.

But, to germinate the (cold stratified) seed, fill a suitable container with moist potting soil. Then scatter the seed on top of the soil and press in with your thumb or hand to ensure good contact. You can then add a dusting of soil if you like, but just make sure the seed isn’t planted deeper than 1/8″ (3 mm). In a lab, Purpletop grass seed has a pretty low germination rate (10-20%), so sow more heavily than you normally would!

If you winter sow the seed, you can expect germination by mid-Spring. If you cold stratify seed in the refrigerator, then you need to plant the seed once temperatures are regularly getting into the 70’s during the day. You can expect a 10-20% germination rate at the end of a four week period^[6].

 

Direct Sowing Purpletop seed

For direct sowing Purpletop, you just need to scatter seed on a cleared/disturbed site in late Fall.  Rake the dirt a little bit with a metal rake.  You really can just get on your knees and extend the rake out to the soil, then just drag it back and forth.  The weight of the rake will sufficiently stir up the soil.  Then, scatter the seed.  Finally, just walk over it.

Below is a short video showing me winter sow some purpletop in pots from a couple of years ago.  But is shows all the steps you need to do.

Where to buy

Unfortunately this grass is unlikely to be found in nurseries, even ones that specialize in natives. It just isn’t that showy as a specimen. Most likely you’re going to need to grow this from seed.

We have ordered a variety of native flower seeds from Everwilde Farms, which you can order right from Amazon through our link on our RECOMMENDED PRODUCTS PAGE. (We may earn a small commission when you purchase through our links, at no cost to you. This helps support our website.)

How to save Purpletop Seed

To save Purpletop seed, simply find a mature plant in Autumn. The seedheads will be ready once the panicles change from purple to a brown-white color. Then, just run your hand along the stalk from below the seedheads and over them. This will effectively strip the seeds. You can store the dry seed in a cool dry place for a couple years.

Fauna

A number of Skipper moth caterpillars feed on the foliage of Purpletop including the Crossline Skipper (Polites origenes), Zabulon Skipper (Poanes zabulon), Little Glassywing (Pompeius verna), Common Wood Nymph (Cercyonis pegala)[host]. Additionally there are several other species of insect that feed on the leaves and seeds^[4]. 

Besides insects, birds will eat the seeds.  And other small animals and birds can use the grass as cover^[2].

Uses for Purpletop

This grass is very showy when planted in dense groupings.  If you have the space and grow a large number of Purpletop, or even just a tight cluster you can be treated to the beautiful purple hue in early Fall.  You’re going to need a lot of this grass to accomplish this visual effect.

But there are other reasons to add this grass to a meadow or yard. The base leaves of the grass are attractive, and that is the part that will host the butterfly caterpillars. And, the lower parts of the plant don’t get tall like Little Bluestem or Big Bluestem. So, you can have a shorter native grass that directly supports pollinators.

Finally, it is a tough plant with a large fibrous root system. And that alone can be reason to plant as it can help reduce erosion or stabilize an exposed slope.

Find more native grasses here