WateringTimesWatering plan, $19
Polygala myrtifolia, WUCOLS IV

How often to water myrtle-leaf milkwort in California

In July on the north-central coast, established myrtle-leaf milkwort in loam needs a deep watering about every 13 days: about 8.8 gallons each time for a plant 4 feet across, about 4.6 gallons a week. Myrtle-leaf milkwort, also sold as sweet pea shrub, is a dense evergreen shrub from South Africa that reaches 8 to 12 feet each way. Its rich purple flowers have two wing-like petals around a lacy crest and bloom much of the year, peaking in spring. It handles wind and coastal sea spray, and grows in sun or part shade.

ShrubRated for 2 of 6 zones

How often to water myrtle-leaf milkwort, month by month

Your city
Plant width
4 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 myrtle-leaf milkwort 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 3 inches down under the shrub in summer means myrtle-leaf milkwort wants a deep soak
  • Leaves drooping and fewer flowers in a long dry spell point to thirst
  • Leaf tips browning after a cold night point to frost, not water
  • Yellowing leaves over soggy soil point to too much water

How to water it

  • Soak slowly so water sinks well into the root zone, then wait for the surface to dry
  • Give occasional summer water once established
  • Plant in sun or part shade in well-drained soil
  • Use it where wind and salt spray rule out other shrubs
  • Give it room to reach full size

Through the seasons

Water a new shrub regularly through its first summer. Established plants are fairly drought tolerant but look their best with at least occasional summer water. Bloom runs through most of the year, strongest in spring. It is hardy only to about 20 to 25 degrees F. WUCOLS rates myrtle-leaf milkwort moderate water on the north-central coast and the south coast. WUCOLS has not evaluated it for the Central Valley, South Inland, the high desert or the low desert.

In pots

Myrtle-leaf milkwort can grow in a large container on a sunny or lightly shaded patio, though it gets big. Use a well-drained mix. Water when the top couple of inches dry, until it drains out the bottom. In summer, check every few days. Do not let water collect in the saucer. On cold nights, move it to shelter. In winter, water when the mix dries and rain falls short.

1 Your climate zone six WUCOLS zones, each from its own reference city
Not ratedWUCOLS does not rate Myrtle-leaf Milkwort for the Central Valley zone
A year
no figure
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses

WUCOLS lists Myrtle-leaf Milkwort as not evaluated for the Central Valley zone, so no monthly figure is computed here.

Monthly water need by climate zone

Myrtle-leaf Milkwort: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.37–0.78–––
Feb0.53–0.81–––
Mar0.87–1.15–––
Apr1.18–1.4–––
May1.46–1.61–––
Jun1.61–1.74–––
Jul1.61–1.98–––
Aug1.49–1.86–––
Sep1.24–1.49–––
Oct0.87–1.15–––
Nov0.47–0.84–––
Dec0.31–0.65–––
Year12–15.5–––

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 16

Rated not evaluated in the Central Valley, like myrtle-leaf milkwort. Plants that drink alike can share one valve and one schedule.

Formosa Sugar PalmArenga englerinot rated, Central Valleyno Central Valley ratingChilean Feather BambooChusquea culeou (C. breviglumis)not rated, Central Valleyno Central Valley ratingBlackbrushColeogyne ramosissimanot rated, Central Valleyno Central Valley ratingGlaucous Scorpion VetchCoronilla valentina glaucanot rated, Central Valleyno Central Valley ratingWillowleaf CotoneasterCotoneaster salicifoliusnot rated, Central Valleyno Central Valley ratingMadagascar SagoCycas thouarsii (SHADE)not rated, Central Valleyno Central Valley ratingIrish HeathDaboecia cantabricanot rated, Central Valleyno Central Valley ratingButterfly PalmDypsis lutescens (Areca)not rated, Central Valleyno Central Valley ratingUmbrella BambooFargesia murielaenot rated, Central Valleyno Central Valley ratingBlue Fountain BambooFargesia nitida (Sinarundinaria nitida) (BAMBOO)not rated, Central Valleyno Central Valley ratingPrickly HeathGaultheria mucronata (Pernettya mucronata)not rated, Central Valleyno Central Valley ratingOtterbossieGossypium harknessiinot rated, Central Valleyno Central Valley ratingBox-leaved HollyIlex crenatanot rated, Central Valleyno Central Valley ratingBellyache BushJatropha gossypiifolianot rated, Central Valleyno Central Valley ratingMountain LaurelKalmia latifolianot rated, Central Valleyno Central Valley ratingBarbados CherryMalpighia glabranot rated, Central Valleyno Central Valley rating
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes myrtle-leaf milkwort, 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 water does myrtle-leaf milkwort need per day?

In July on the north-central coast, established myrtle-leaf milkwort needs about 0.7 gallons a day for a plant 4 feet across and about 2.6 gallons a day for a plant 8 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 myrtle-leaf milkwort change across California?

Yes. WUCOLS rates myrtle-leaf milkwort separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, not evaluated in the Central Valley zone, moderate water in the South Coastal zone, not evaluated 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.

Does myrtle-leaf milkwort bloom all year?

It blooms during most of the year, with a peak in spring. Occasional water keeps it flowering. Light pruning helps.

Is myrtle-leaf milkwort good near the ocean?

Yes, it grows along the seashore in South Africa and tolerates wind and sea spray. It suits coastal gardens. Water it occasionally.

How cold hardy is myrtle-leaf milkwort?

It is hardy to about 20 to 25 degrees F, with tip damage near 20 degrees. It suits mild coastal winters. Protect young plants.

How big does myrtle-leaf milkwort get?

It grows 8 to 12 feet tall and wide, often 10 feet or more. That is larger than the common hybrid polygala. Give it room.

How is it different from the common polygala?

It is a parent of the common hybrid polygala. It is a bigger plant with darker leaves and larger flowers. Care is similar.

More plant watering guides

Japanese HornbeamChilean Feather BambooAmerican YellowwoodAnemone ClematisBlackbrushPagoda DogwoodGiant DogwoodGlaucous Scorpion Vetch

Sources