Purple Top Grass – Facts, How to Grow, Information

Purple Top is a perennial grass that grows 3-5′ tall and puts on a beautiful display of purple colors from the seed heads in Late Summer and Early Fall.  This is definitely one of our ‘ornamental’ Native Grasses when planted densely.  Native to North America, this grass is tolerant of salt making at very common along the roadsides.  Although many grasses are hard to identify, this one is quite easy to spot along roads when it blooms in late summer, as it will make a purple hue along the ditch or shoulder.

Purple Top Grass growing in my neighborhood

Purple Top Grass Facts

  • Native range is from the Rocky Mountains to the Atlantic Ocean
  • Is hardy from zones 3-10.  Check you USDA garden zone here.
  • Will grow 5′ tall if unmowed
  • Purple Top 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 Purple Top Grass is Tridens Flavus

Purple Top Physical Description and Identification

When not in bloom it is a fairly plain and unassuming grass, that can easily be confused for other 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.Purple Top Grass Bloom Tridens Flavus

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.  The leaves wrap around the stalk, more than 50% of the diameter usually.

Purple Top Foliage, well before blooming.

Flower

At the top of the stalk there will be spikelet flowers (that eventually turn purple).  These spikelets are attached to stems that are up to 1′ long.  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.

Purple Top Growing Conditions

This is a great colonizing grass to grow in hot and dry conditions.  Purple Top prefers full sun.  It is very drought tolerant, and prefers dry soil.  It will also grow well in medium moist areas.  Do not plant this in rain gardens or along ponds, streams, etc.

For soil types, it is highly versatile in that it has no problem growing well in clay or loam.  But doesn’t do as well in sandy conditions.

How to care  for Purple Top

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

Maintenance

Cut back in Spring once temperatures have warmed up and insects have emerged.  You can cut it back sooner, like in Autumn if you prefer.  But it is better to wait if you can.  This is because many insects overwinter in dead foliage from the previous season.  So, if you want to help your local beneficial insect population, let the grass stand until Spring.Purple Top Tridens Flavus

How to Establish Purple Top from Seed

To germinate Purple Top Seed in pots, plant seed 1/8″ deep (3 mm).  Then set the pots outside in the winter.  This is called winter sowing, and is a very effective way to stratify your seed.  A short video describing how I wintersow most of my seeds is here.

Direct Sowing Purple Top

For direct sowing Purple Top, you just need to scatter seed on a cleared site in late Fall.  Rake the dirt a little bit (6 mm) 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 purple top in pots from a couple of years ago.  But is shows all the steps you need to do.

 

Garden Uses for Purple Top

This grass is very showy when planted en mass.  If you have the space and grow a large number of Purple Top, or even just a tight cluster you can be treated to the beautiful purple hue in early Fall.  But, if you just need a rugged grass to stabilize a slope, or help manage erosion this is a good choice.

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.  The purple top helps add cover for wildlife throughout the winter.  And the seeds provide food for birds and other animals.  Click on the image below to learn how to make your own Backyard Micro-Prairie!

How To Make a Micro-Prairie

Fauna

A number of Skipper moth caterpillars feed on the foliage of Purple Top, as well as several other species of insect.  Birds will eat the seeds.  Additionally other small animals can use the grass as cover.

Pests and diseases

None.  Any damage from insects will not significantly effect the bloom in late Summer / Early Fall.  I’ve never seen, nor am aware of any disease that can harm this grass.

Purple Top Grass Reference Table
Common NamePurple Top Grass
Scientific nameTridens flavus
Bloom TimeLate Summer
Bloom Duration2-3 weeks
ColorDark Purple
Bloom Size¼-1/2” spikelets (6-12 mm)
CharacteristicsIndividual spikelets attached to a small stem that branches from the top.  There are multiple stems per plant.
Height3-5’ (1-1.5 m)
Spacing/Spread0.5-3’ (0.3m – 1 m)  Plant more densely for a showier display
Light RequirementsFull Sun / Partial Shade
Soil TypesClay, Loam
MoistureDry to Medium
MaintenanceNone.  Cut back in Spring after insects have emerged
Typical UseMeadow, prairie, roadside, erosion control
Fauna AssociationsCaterpillars and other insects feed on foliage
Larval HostZabulon Skipper, Crossline Skipper, Homomok Skipper, Little Glassywing, Wood Nymph
Sowing Depth0-1/8” (0-3 mm)
Stratification60 days cold stratification.  Or direct sow in Autumn/Winter
Native RangeUSDA Zones 3-10
NotesMass plantings look really cool of this grass

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