WateringTimesWatering plan, $19
Lycianthes rantonnetii, WUCOLS IV

How often to water blue potato bush in California

In July in the Central Valley, established blue potato bush in loam needs a deep watering about every 8 days: about 8.8 gallons each time for a plant 4 feet across, about 7.6 gallons a week. Blue potato bush, also called Paraguay nightshade, is a fast-growing evergreen shrub from Paraguay, Argentina, Bolivia and southern Brazil. Purple-blue flowers with yellow centers open in summer and fall, and for much of the year in mild climates. It looks best with regular to occasional water. It can survive on less when it must, but it will not look its best.

ShrubRated for 4 of 6 zones

How often to water blue potato bush, 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 blue potato bush 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 outer branches means blue potato bush is ready for a deep soak
  • Soft new shoots that hang limp into the evening point to a dry root zone in summer heat
  • Yellowing leaves and wilting over soil that stays soggy point to poor drainage rather than thirst
  • Wilting shoot tips on a potted standard after a hot, windy day mean the small root ball has dried out

How to water it

  • Water blue potato bush at the base with drip or a slow hose instead of spraying the lax branches
  • Soak until the soil is moist about 18 inches down, then let the top few inches dry before the next soak
  • Spread wood chip mulch over the root zone, keeping it a few inches back from the main stems
  • Plant it in full sun in almost any soil with decent drainage, and avoid low spots that hold winter water
  • Shift drip emitters outward as the shrub widens, since this fast grower widens quickly

Through the seasons

Water a new blue potato bush deeply through its first summer while roots spread into the bed. An established shrub needs regular to occasional soakings to keep flowering and full. It stays evergreen, so it keeps using some water through winter. Bloom runs through summer and fall, so those months are when soil checks matter most. Winter rain covers the cool months on the coast and in the Central Valley. It is best suited to mild winters, and a hard freeze can damage it. WUCOLS rates blue potato bush moderate water on the north-central coast, in the Central Valley, on the south coast and in South Inland. WUCOLS marks it as not suited to the high desert. WUCOLS has not evaluated it for the low desert.

In pots

Blue potato bush is often grown as a standard, a shrub trained to a single trunk in a pot. Use a wide, heavy container with drainage holes so the top-heavy head does not tip in wind. Check the mix 2 inches down every few days in summer, and daily in Central Valley or South Inland heat. Water until it drains from the holes, then empty the saucer. Feed it regularly through the growing season. In winter, let the mix dry a little more between soakings, and move the pot under cover before a hard frost.

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
0.671.32.02.70.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.671.32.02.70.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Blue Potato Bush: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.780.78––
Feb0.530.650.810.87––
Mar0.871.091.151.3––
Apr1.181.521.41.61––
May1.462.081.611.95––
Jun1.612.481.742.29––
Jul1.612.671.982.51––
Aug1.492.391.862.33––
Sep1.241.81.491.86––
Oct0.871.181.151.33––
Nov0.470.560.840.9––
Dec0.310.340.650.68––
Year1217.1115.518.41––

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 moderate water in the Central Valley, like blue potato bush. Plants that drink alike can share one valve and one schedule.

RosesRosa hybrids..bushmoderate water, Central Valley2.67 gal/sq ft in JulyAzaleasRhododendron spp. (CA native and non-native spp.)moderate water, Central Valley2.67 gal/sq ft in JulyCamelliasCamellia japonica (SHADE IN DESERT)moderate water, Central Valley2.67 gal/sq ft in JulyGardeniasGardenia spp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBird of ParadiseStrelitzia reginae (shade in desert)moderate water, Central Valley2.67 gal/sq ft in JulyHibiscusHibiscus rosa-sinensismoderate water, Central Valley2.67 gal/sq ft in JulySago PalmCycas revolutamoderate water, Central Valley2.67 gal/sq ft in JulyStar JasmineTrachelospermum jasminoides and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyArborvitaeThuja occidentalis ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBambooBambusa spp.moderate water, Central Valley2.67 gal/sq ft in JulyLilacsSyringa hybrids (including Descanso hybrids)moderate water, Central Valley2.67 gal/sq ft in JulySpireaSpiraea spp. (CA native and non native spp.)moderate water, Central Valley2.67 gal/sq ft in JulyButterfly BushBuddleja davidii and hybridsmoderate water, Central Valley2.67 gal/sq ft in JulySageSalvia officinalis and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyRed BuckeyeAesculus paviamoderate water, Central Valley2.67 gal/sq ft in JulyWestern ServiceberryAmelanchier alnifoliamoderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 16

Rated lower than blue potato bush in the Central Valley. Worth a look for a new bed or a lawn replacement.

LavenderLavandula spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRosemaryRosmarinus officinalislow water, Central Valley1.07 gal/sq ft in JulyBougainvilleaBougainvillea & spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyOlive TreesOlea europaea ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyCrape MyrtleLagerstroemia spp., hybrids & cvs.low water, Central Valley1.07 gal/sq ft in JulyLantanaLantana camara ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in JulyAloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRussian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySagebrushArtemisia spp. (shrubby)low water, Central Valley1.07 gal/sq ft in JulyWild PrivetLigustrum vulgarelow water, Central Valley1.07 gal/sq ft in JulyCoralberrySymphoricarpos orbiculatus (SHADE)low water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow water, Central Valley1.07 gal/sq ft in JulyBlue Leaf WattleAcacia salignalow 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 blue potato bush, 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 blue potato bush in summer?

In July, established blue potato bush in loam needs a deep watering about every 8 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 blue potato bush need per day?

In July in the Central Valley, established blue potato bush needs about 1.1 gallons a day for a plant 4 feet across and about 4.3 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 blue potato bush change across California?

Yes. WUCOLS rates blue potato bush separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate 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 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 blue potato bush poisonous?

Yes. All parts can cause severe discomfort if eaten, and red berries can follow the flowers. Wear gloves when you prune it and wash your hands afterward. Plant it away from where small children play.

How big does blue potato bush get?

Left alone it can reach 10 to 12 feet tall. It takes pruning well, so it is easy to keep smaller. Tip prune or lightly shear it often to keep it tight and bushy.

Can blue potato bush be a small tree?

Yes. It is often trained up as a small patio tree or a potted standard. Its stems are lax, so give a young trunk a stake until it firms up.

Do deer eat blue potato bush?

It resists deer browsing. That makes it a useful flowering shrub in gardens where deer visit. Resistant does not mean deer proof, so watch new plantings.

Is blue potato bush the same as Solanum rantonnetii?

Yes. It was long sold as Solanum rantonnetii before botanists moved it to Lycianthes. It reached California gardens through a Santa Barbara nursery in 1906.

Is blue potato bush fragrant?

The flowers are lightly fragrant. The scent is easiest to notice when the shrub is in full bloom. Plant it near a path or patio to enjoy it.

More plant watering guides

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Sources