WateringTimesWatering plan, $19
Alyssum montanum, WUCOLS IV

How often to water mountain alyssum in California

In July in the Central Valley, established mountain alyssum in loam needs a deep watering about every 14 days: about 1.5 gallons each time for a plant 2 feet across, about 0.8 gallons a week. Mountain alyssum is a low, mat-forming evergreen perennial about 6 inches tall, with small, hairy, gray leaves. In late spring and summer it is covered in rounded clusters of scented, soft yellow flowers. A plant of European mountains, it wants full sun and the sharp drainage of a rock garden.

PerennialRated for 4 of 6 zones

How often to water mountain alyssum, 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 mountain alyssum 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 foot 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 2 inches down beneath the mat in summer signals mountain alyssum needs a soak
  • Gray leaves looking flat and limp in afternoon heat can indicate thirst
  • Flowers fading quickly with crisp edges can follow a dry spell during bloom
  • A mat browning from the center while the soil stays damp points to rot from poor drainage

How to water it

  • Water around the mat with a gentle hose or low drip, keeping the foliage dry
  • Wet the soil 4 to 6 inches down, then let the top inch or two dry
  • Plant in sandy or loamy soil with fast drainage, in a rock garden or wall pocket
  • Use a stone or gravel mulch so the hairy leaves stay off wet soil
  • Cut back lightly after flowering to keep the mat compact

Through the seasons

Water a new plant lightly and often until it roots in, then let the soil dry between deeper soaks. Established mats handle dry spells well. It is evergreen, holding its gray leaves through winter, and flowers in late spring and summer. It is very cold hardy, so drainage matters more than frost. WUCOLS rates mountain alyssum low water on the north-central coast and in the Central Valley. The south coast and South Inland carry a moderate water rating. WUCOLS marks it as not suited to the high desert or the low desert.

In pots

Mountain alyssum suits a shallow trough, bowl or wall pot filled with gritty mix. A thin layer of mix dries fast, so in summer check it every few days and water once the top inch is dry. Let excess drain away and keep the saucer empty. Shear lightly after bloom. In winter, water rarely and keep the pot out of standing rain. Repot into fresh gritty mix when the mat outgrows the container.

1 Your climate zone six WUCOLS zones, each from its own reference city
1.07gal per sq ft in JulyLow water use in the Central Valley zone
A year
6.84 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.631.31.92.50.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.631.31.92.50.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Mountain Alyssum: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.780.78––
Feb0.210.260.810.87––
Mar0.350.431.151.3––
Apr0.470.611.41.61––
May0.580.831.611.95––
Jun0.640.991.742.29––
Jul0.641.071.982.51––
Aug0.60.951.862.33––
Sep0.50.721.491.86––
Oct0.350.471.151.33––
Nov0.190.220.840.9––
Dec0.120.140.650.68––
Year4.86.8415.518.41––

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 16

Rated low water in the Central Valley, like mountain alyssum. Plants that drink alike can share one valve and one schedule.

AgapanthusAgapanthus orientalislow water, Central Valley1.07 gal/sq ft in JulyGeraniumsPelargonium x hortorum and cvs.low water, Central Valley1.07 gal/sq ft in JulySalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in JulyIrisesIris germanicalow water, Central Valley1.07 gal/sq ft in JulySucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRussian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyYarrowAchillea millefolium (non-native hybrids)low water, Central Valley1.07 gal/sq ft in JulySilver SageSalvia argentealow water, Central Valley1.07 gal/sq ft in JulyPurple MulleinVerbascum phoeniceumlow water, Central Valley1.07 gal/sq ft in JulySilvery YarrowAchillea clavennaelow water, Central Valley1.07 gal/sq ft in JulyFern Leaf YarrowAchillea filipendulinalow water, Central Valley1.07 gal/sq ft in JulyCalifornia Native YarrowAchillea millefolium (CA native cultivars)low water, Central Valley1.07 gal/sq ft in JulyWoolly YarrowAchillea tomentosalow water, Central Valley1.07 gal/sq ft in JulyPerennial HollyhockAlcea rosea cvs.low water, Central Valley1.07 gal/sq ft in JulyMountain Lady's MantleAlchemilla alpinalow water, Central Valley1.07 gal/sq ft in JulyLady's MantleAlchemilla mollislow 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 mountain alyssum, 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 mountain alyssum in summer?

In July, established mountain alyssum in loam needs a deep watering about every 14 days in the Central Valley, about every 7 days on the south coast and about every 6 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 mountain alyssum need per day?

In July in the Central Valley, established mountain alyssum needs about 0.1 gallons a day for a plant 2 feet across and about 0.4 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 mountain alyssum change across California?

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

Is mountain alyssum the same as sweet alyssum?

No, sweet alyssum is a different plant, usually grown as an annual. Mountain alyssum is a hardy evergreen perennial with yellow flowers. It needs a sunny, well-drained spot.

Where should I plant mountain alyssum?

It is ideal for rock gardens, wall crevices and the edge of gravel paths. Give it full sun and sharp drainage. Avoid beds with frequent sprinklers.

Should I cut back mountain alyssum after flowering?

Yes, cut it back lightly after bloom. That keeps the mat dense and tidy. It does not change how deep to check the soil.

Does mountain alyssum have pest problems?

It is generally free of pests and diseases. Rot from wet soil is the main risk. Fix drainage before adding water.

How do I propagate mountain alyssum?

Take softwood cuttings or sow seed. Keep cuttings lightly moist in gritty mix until they root. Plant them out in a sunny, well-drained spot.

More plant watering guides

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Sources