WateringTimesWatering plan, $19
Pennisetum alopecuroides ssp. & cvs., WUCOLS IV

How often to water black pennisetum in California

In July in the Central Valley, established black pennisetum needs about 1.9 gallons a week for a plant 2 feet across. Black pennisetum is a warm-season fountain grass from East Asia that grows as an arching clump of narrow leaves. Bristly, bottlebrush flower spikes in silvery to pinkish white arch out above it in late summer. Once established it handles dry spells, and it also grows in moist ground. It may be sold under the newer genus name Cenchrus.

Ornamental grassRated for 6 of 6 zones

How often to water black pennisetum, month by month

Your city
Plant width
2 ft
Your soil

Type your city above and the days between waterings and the gallons appear here, worked out from your city's climate table. Or read the figures by climate zone further down.

Every month, on your water days. The personal plan prints this for black pennisetum and the rest of your yard, on the days your water supplier allows.Get the plan for $19

How this is worked out: the plant’s WUCOLS rating times your city’s climate for the month, over the area the plant covers. Skip a watering after a good soaking rain.

Which soil do you have?

Dig down a few inches, take a handful of moist soil and squeeze it.

  • Sandy: gritty, falls apart when you open your hand, will not form a ball.
  • Loam: forms a soft ball that crumbles when you poke it.
  • Clay: forms a firm, sticky ball and squeezes out into a ribbon between thumb and finger.

Still not sure? Pick loam. Most garden beds sit between sand and clay.

How to measure plant width

A shrub with its width marked from one side to the other and the circle under it shaded blue

Measure across the plant, from the tips of the leaves on one side to the tips on the other.

Water the whole area the plant covers, shown in blue. The gallons here cover that area.

A wider plant means more gallons each watering, not more waterings. While it is young, measure again each spring.

How to tell it needs water

  • Soil dry 3 to 4 inches down at the edge of the clump in summer means it is time for a deep soak
  • Leaf blades folding or curling in afternoon heat, with dry soil below, can point to a thirsty clump
  • Leaves turning golden in fall and then beige are the normal seasonal change for this warm-season grass, not thirst
  • Few or no flower spikes by late summer more often trace to heavy shade than to a watering problem
  • Soil that stays soggy around the crown for days after a soak means the bed drains poorly and the next soak should wait

How to water it

  • Water at the base of the clump and out to its edge with drip or a slow hose rather than overhead spray
  • Soak until water reaches about 12 inches down, then let the top few inches dry before the next soak
  • Spread a thin layer of mulch around the clump, leaving the center of the crown uncovered
  • Plant it in full sun in soil that drains well, since too much shade cuts flowering
  • Widen the watered ring as the clump spreads, and cut the old leaves down in late winter before new shoots appear

Through the seasons

Water a new clump deeply through its first summer, until roots spread well past the nursery root ball. Established clumps handle dry spells, though summer soil checks still matter where the rating is moderate. New shoots start in spring, flower spikes arch out in late summer, and leaves turn golden, then beige, in fall. Cut the old growth down in late winter. Winter rain covers the cool months on the north-central coast, on the south coast and in the Central Valley. In both deserts, check the soil during dry winter spells. WUCOLS rates it low water on the north-central coast and in South Inland. It rates moderate water in the Central Valley, on the south coast, in the high desert and in the low desert.

In pots

Black pennisetum can grow in a large container, and a compact cultivar keeps the clump in better proportion to the pot. Check the mix 2 inches down every few days in summer, and daily in valley or desert heat. Water until it runs from the drainage holes, then empty the saucer. A clump that fills the pot with roots dries out fast, so divide it or move it up a size. In winter the tan, resting clump uses little water, so let the mix dry further between soakings.

1 Your climate zone six WUCOLS zones, each from its own reference city
2.67gal per sq ft in JulyModerate water use in the Central Valley zone
A year
17.11 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.761.52.33.00.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.761.52.33.00.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Black Pennisetum: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.40.780.310.740.78
Feb0.210.650.810.350.930.93
Mar0.351.091.150.521.461.52
Apr0.471.521.40.641.891.95
May0.582.081.610.782.392.45
Jun0.642.481.740.922.852.79
Jul0.642.671.9813.042.85
Aug0.62.391.860.932.792.6
Sep0.51.81.490.742.142.08
Oct0.351.181.150.531.461.49
Nov0.190.560.840.360.930.96
Dec0.120.340.650.270.650.68
Year4.817.1115.57.3721.2721.08

How this is worked out: the WUCOLS water rating for each zone times that zone’s climate for the month. A dash means WUCOLS does not rate the plant there. The figures are what the plant uses, before sprinkler losses.

Plants with the same water needs 7

Rated moderate water in the Central Valley, like black pennisetum. Plants that drink alike can share one valve and one schedule.

Tall Oat GrassArrhenatherum elatiusmoderate water, Central Valley2.67 gal/sq ft in JulyPurple Moor GrassMolinia caeruleamoderate water, Central Valley2.67 gal/sq ft in JulySheep FescueFestuca ovina and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyCreeping Red FescueFestuca rubra ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyEulalia GrassMiscanthus sinensis ssp. & cvsmoderate water, Central Valley2.67 gal/sq ft in JulySwitch GrassPanicum virgatum ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBlood GrassImperata cylindrica ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 7

Rated lower than black pennisetum in the Central Valley. Worth a look for a new bed or a lawn replacement.

Quaking GrassBriza medialow water, Central Valley1.07 gal/sq ft in JulyTufted HairgrassDeschampsia cespitosa and cvs.low water, Central Valley1.07 gal/sq ft in JulyJune GrassKoeleria macrantha (cristata)low water, Central Valley1.07 gal/sq ft in JulyFalse Esparto GrassLygeum spartumlow water, Central Valley1.07 gal/sq ft in JulyBlue FescueFestuca glauca ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyBaltic RushJuncus balticuslow water, Central Valley1.07 gal/sq ft in JulyGiant Needle GrassStipa gigantealow water, Central Valley1.07 gal/sq ft in July
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes black pennisetum, your sprinkler type and the month, and gives the minutes per water day for that supplier's schedule. Or put it in a zone of the personal watering plan and get all twelve months printed.

Questions people ask

How much should I water black pennisetum in summer?

In July, established black pennisetum needs about 1.9 gallons in the Central Valley, 1.4 gallons on the south coast and 0.7 gallons in the South Inland zone each week, for a plant 2 feet across. Water deeply and let the top of the soil dry before the next watering. Skip a watering after a soaking rain.

How much water does black pennisetum need per day?

In July in the Central Valley, established black pennisetum needs about 0.3 gallons a day for a plant 2 feet across and about 1.1 gallons a day for a plant 4 feet across. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Does watering for black pennisetum change across California?

Yes. WUCOLS rates black pennisetum separately for each of the six California climate zones: low water in the North-Central Coastal zone, moderate water in the Central Valley zone, moderate water in the South Coastal zone, low water in the South Inland zone, moderate water in the High and Intermediate Desert zone, moderate water in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

When should I cut back black pennisetum?

Cut the old foliage to the ground in late winter, before new shoots appear. The tan leaves and seed heads can stand through fall and early winter for show. After cutting, water only once new shoots are growing and the soil below is dry.

Does black pennisetum spread by seed?

Yes. It can self-seed aggressively, and in warm-winter climates it can turn weedy. Seed heads usually hold until late fall or early winter before they shatter, so cut them before then. A cultivar bred to be sterile avoids the problem.

Is black pennisetum the same as Cenchrus?

Yes. Botanists have moved Pennisetum alopecuroides into the genus Cenchrus, so the same grass may carry the label Cenchrus alopecuroides. Plants sold under either name need the same care.

Why is my black pennisetum not flowering?

Too much shade is a common cause, since it blooms best in full sun and may not flower in heavy shade. The spikes also come late, from late summer on. A clump that looks bare of flowers in spring is simply not there yet.

Can black pennisetum grow near the coast?

Yes. It is listed as slightly salt tolerant and is planted in coastal gardens. On the north-central coast, WUCOLS rates it low water.

Do deer eat black pennisetum?

It is highly resistant to deer grazing. That makes it useful in open, unfenced beds and on slopes, where it also helps control erosion. Deer resistance does not change how much water it needs.

More plant watering guides

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Sources