WateringTimesWatering plan, $19
Persicaria capitata (Shade in San Diego), WUCOLS IV

How often to water pink knotweed in California

In July in the Central Valley, established pink knotweed in loam needs a deep watering about every 5 days: about 2.2 gallons each time for a plant 2 feet across, about 3.0 gallons a week. Pink knotweed, also called pink bobbles, is a low groundcover from South Asia in the knotweed family. Its round clusters of tiny pink flowers sit above the leaves and provide nectar and pollen for bees. WUCOLS adds a note calling for shade around San Diego, so it suits partly shaded spots in warm gardens.

Ground coverRated for 4 of 6 zones

How often to water pink knotweed, 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 pink knotweed and the rest of your yard, on the days your water supplier allows.Get the plan for $19

How this is worked out: established roots fill the top 1.5 feet of soil, and you water again when that soil has dried halfway. Loam soil holds about 1.5 inches of water per foot. Water the whole area the plant covers, and 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 an inch or two down under the mat in summer means pink knotweed needs water
  • Leaves wilting by midday in sun point to dry soil or too much heat
  • Leaves scorching in hot afternoon sun point to a site that is too exposed
  • Stems rotting in soggy soil point to overwatering

How to water it

  • Water the mat evenly with drip or a soaker
  • Wet the soil about 6 inches deep, then let the top inch dry
  • Give it partial shade in hot inland and southern gardens
  • Use it as a low groundcover or to spill from pots
  • Trim stray stems at the edges

Through the seasons

Water new plantings regularly until they spread. Established mats want steady water through the warm months, with the most in the hot Central Valley. Shade helps it hold up in southern heat. Bees visit the flowers through the warm season. WUCOLS rates pink knotweed moderate water on the north-central coast, on the south coast and in South Inland. In the Central Valley it carries a high water rating. WUCOLS has not evaluated it for the high desert or the low desert.

In pots

Pink knotweed spills nicely from pots and hanging baskets, where its pink pompoms can be seen up close. Use a well-drained mix with compost. Water when the top inch dries, until it drains through. In summer, small pots may need water daily. Keep the pot in part shade where afternoons are hot. Empty the saucer. In winter, water only when the mix dries.

1 Your climate zone six WUCOLS zones, each from its own reference city
4.27gal per sq ft in JulyHigh water use in the Central Valley zone
A year
27.38 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
1.12.13.24.30.64JAN1.04FEB1.74MAR2.43APR3.32MAY3.97JUN4.27JUL3.82AUG2.88SEP1.88OCT0.89NOV0.55DEC1.12.13.24.30.64JFM2.43AMJ4.27JAS1.88OND
Gallons per square foot per month, Central Valley. Peak 4.27 in Jul, 27.38 a year.

Monthly water need by climate zone

Pink Knotweed: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.640.780.78––
Feb0.531.040.810.87––
Mar0.871.741.151.3––
Apr1.182.431.41.61––
May1.463.321.611.95––
Jun1.613.971.742.29––
Jul1.614.271.982.51––
Aug1.493.821.862.33––
Sep1.242.881.491.86––
Oct0.871.881.151.33––
Nov0.470.890.840.9––
Dec0.310.550.650.68––
Year1227.3815.518.41––

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 3

Rated high water in the Central Valley, like pink knotweed. Plants that drink alike can share one valve and one schedule.

Bog RosemaryAndromeda polifoliahigh water, Central Valley4.27 gal/sq ft in JulyBaby's TearsSoleirolia soleirolii (SHADE)high water, Central Valley4.27 gal/sq ft in JulyBellflowerCampanula & spp. and cvs.high water, Central Valley4.27 gal/sq ft in July

Similar plants that need less water 16

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

Star JasmineTrachelospermum jasminoides and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyHoneysuckleLonicera japonicamoderate water, Central Valley2.67 gal/sq ft in JulyIvyHedera helixmoderate water, Central Valley2.67 gal/sq ft in JulyStrawberriesFragaria spp. & cvs. (CA native and non-natives species)moderate water, Central Valley2.67 gal/sq ft in JulyCarpet BugleAjuga reptans (shade)moderate water, Central Valley2.67 gal/sq ft in JulyGreen Supreme ManzanitaArctostaphylos uva-ursi 'Green Supreme'moderate water, Central Valley2.67 gal/sq ft in JulyMassachusetts ManzanitaArctostaphylos uva-ursi 'Massachusetts'moderate water, Central Valley2.67 gal/sq ft in JulySerbian BellflowerCampanula poscharskyanamoderate water, Central Valley2.67 gal/sq ft in JulyBunchberryCornus canadensismoderate water, Central Valley2.67 gal/sq ft in JulyKenilworth IvyCymbalaria muralismoderate water, Central Valley2.67 gal/sq ft in JulyCranesbillGeranium spp.moderate water, Central Valley2.67 gal/sq ft in JulyGreen CarpetHerniaria glabramoderate water, Central Valley2.67 gal/sq ft in JulySpotted DeadnettleLamium maculatummoderate water, Central Valley2.67 gal/sq ft in JulyLemon BalmMelissa officinalismoderate water, Central Valley2.67 gal/sq ft in JulyJapanese SpurgePachysandra terminalismoderate water, Central Valley2.67 gal/sq ft in JulyMoss PinkPhlox subulatamoderate water, Central Valley2.67 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 pink knotweed, 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 often should I water pink knotweed in summer?

In July, established pink knotweed in loam needs a deep watering about every 5 days in the Central Valley, about every 11 days on the south coast and about every 9 days in the South Inland zone. Sandy soil holds less water, so waterings come closer together. Clay stretches them. Check the soil before each watering and skip one after a soaking rain.

How much water does pink knotweed need per day?

In July in the Central Valley, established pink knotweed needs about 0.4 gallons a day for a plant 2 feet across and about 1.7 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 pink knotweed change across California?

Yes. WUCOLS rates pink knotweed separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, high water in the Central Valley zone, moderate water in the South Coastal zone, moderate water in the South Inland zone, not evaluated in the High and Intermediate Desert zone, not evaluated in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

Is pink knotweed good for bees?

Yes, it provides nectar and pollen for bees and other pollinators. Its pink flower heads are small and round. Keep it blooming with steady water.

Does pink knotweed need shade?

WUCOLS notes that it needs shade in San Diego. Partial shade helps in hot inland gardens too. Watch it in afternoon sun.

Where does pink knotweed come from?

It is native to South Asia. It belongs to the knotweed family. It is grown as a low groundcover.

Can pink knotweed grow in pots?

Yes, it spills well from containers and baskets. Pots dry fast, so check often. Give them part shade.

Why is pink knotweed wilting in the valley?

The Central Valley's heat dries it fast, and WUCOLS rates it high water there. Water more deeply and add afternoon shade. Mulch helps.

More plant watering guides

Chameleon HouttuyniaBaby's TearsBellflowerVine MapleHydrangeaBlueberriesBig Leaf MapleJapanese Sweet Flag

Sources