Watering calculator

The first year decides whether a new tree establishes, and watering is most of the work. Enter how the tree went in, its trunk caliper, the weeks since planting, the soil, and whether any day in the last seven brought more than an inch of rain. The calculator gives the gallons for each watering and how often, says whether the rain replaces one, shows how sand or clay changes the pattern, and counts how much of the establishment period is left. A shrub has a rule of its own: choose Shrub, and the dose comes from the pot it came in and the watering runs for two growing seasons. Every rule is shown with its source, so you can see how the answer was reached.

What you planted A tree is watered by its trunk. A shrub is watered by the pot it came in, and takes about two growing seasons to establish. How it went in Every form follows the same schedule. A root ball dries out faster than the soil around it; a dormant bare-root sapling uses little until it leafs out, so check its soil before each watering. A plant's page says which forms its saplings ship in. Trunk caliper (inches) Trunk diameter 6 inches above the root flare. A pencil-thick seedling is about 0.25, a thumb-thick sapling about 0.75, a garden-center tree 1 to 2. Weeks since planting Sets the schedule: daily for weeks 1 and 2, every 2 to 3 days to week 12, then weekly until established. Sand and clay shift the later two phases. Planted on (optional) The day it went in the ground. The weeks fill in from it, and a copied link or a calendar reminder then opens on the right week. Soil Sand gets half the dose about twice as often after the first two weeks; clay gets the same dose slowly, at longer gaps, after a look at the soil. Loam and silt keep Minnesota's schedule. To tell them apart, squeeze a moist handful: sand falls apart, clay forms a ribbon, loam holds together but crumbles. Rain in the last 7 days Only a day with more than an inch counts, and it replaces the one watering that follows it. So it matters only if it fell inside the schedule's interval: a day, three days or a week. Lighter showers, and rain more than seven days ago, change nothing. No rain gauge? A straight-sided can set out in the open fills an inch deep in an inch of rain.

Numbers update as you type.

The calculator needs JavaScript. The rules it uses come from University of Minnesota Extension and hold for every form of stock. A tree takes 1 to 1.5 gallons per inch of trunk caliper at each watering. It is watered daily for weeks 1 and 2, every 2 to 3 days to week 12, then weekly until established, about 1.5 years per inch of caliper. A shrub takes a quarter to a third of the volume of the pot it came in at each watering, on the same schedule, for at least two growing seasons. A watering is skipped only after more than an inch of rain in a day, and never the week's only watering, which a recent soaking turns into a check of the soil first. On sand the dose is halved and given about twice as often after the first two weeks: every 1 to 2 days to week 12, twice a week after. On clay the same dose is given slowly at longer gaps, after a look at the soil: every 3 to 4 days to week 12, every 7 to 10 days after. Loam keeps the schedule as it stands, and silt is treated as loam. A tree is never counted established in under a year, the calculator's own reading of Colorado State Extension. Winter, from December to February and past the first two weeks: water only once or twice a month, when the ground is not frozen and the weeks before have been dry (Colorado State Extension). After establishment, in a dry spell: a tree takes about 10 gallons per inch of trunk every two weeks (Colorado State Extension). A shrub takes a soaking whenever the soil is dry 6 inches down (University of Maryland Extension).

How to water a new tree

Water the root ball, slowly. For the first few months a potted or balled tree can only drink from the soil it arrived in. Trickle water directly over the ball; a bucket with a small hole, or a hose on a slow drip, works better than a sprinkler.
Check before you water. Push a screwdriver or a trowel about 6 inches into the ball. If the soil there is still moist, skip a day. Container-grown root balls dry out faster than the surrounding soil, so the lawn being damp tells you nothing.
Water in the morning. In the heat of the day more of the water is lost to evaporation.
Give more in hot, windy weeks. Take the higher amount at the shorter gap of each range.
No measuring can? Time how long the hose takes to fill a gallon jug at the trickle you water with. Run it that long for each gallon of the dose.
Bare-root needs the check most. A dormant sapling has no ball to keep wet and uses little water until it leafs out, so the soil test before each watering matters more for it than the calendar. Water it in well at planting, then follow the same schedule as a root ball, watering when the soil is dry about 6 inches down. Bare-root trees on arrival covers the first hour, the first week and the first spring.
Know your soil. Sand drains fast and holds little, so smaller, more frequent drinks keep the root zone moist. Clay takes water in slowly and holds it, so the same amount goes on slowly and less often. A look about 6 inches down comes first, because too much at once waterlogs the planting hole. Loam and silt are the middle ground. To tell them apart, squeeze a moist handful: sand falls apart, clay forms a ribbon, loam holds together but crumbles.
Mulch wide, not deep. Two to three inches of leaf or wood mulch over the root zone, pulled back from the trunk, cuts the water the soil loses to evaporation.
Keep the bark dry. Water the soil, not the trunk, and keep mulch off the bark: bark kept wet can lead to canker and decay.
Widen the ring as the roots spread. After the first few months, water a ring that grows about 18 inches a year, and soak it 8 to 12 inches deep.
Water less in winter. From December to February, water only on ground that is not frozen, after dry weeks, once or twice a month. An evergreen needs a deep watering before the ground freezes if the fall was dry.
Taper off. Once a tree has been in the ground about a year and a half per inch of caliper, and at least a year, it can usually fend for itself except in drought. A shrub takes at least two growing seasons. In a dry spell after that, an established tree takes a deep soaking under its branches every two weeks.

The calculator follows University of Minnesota Extension's guidance for newly planted trees: 1 to 1.5 gallons per inch of trunk caliper at each watering. It waters daily for the first two weeks, every two to three days to week twelve and weekly until established. A watering is skipped only after more than an inch of rain in a day. For a shrub the same page gives a rule of its own, which the Shrub setting follows. Its rule is to "apply a volume of water that is one-quarter to one-third of the volume of the container that the shrub was purchased in", at the same intervals. That goes on until the roots have spread as wide as the top, which "will likely take at least two growing seasons"; the calculator counts that as two years from planting. A shrub that came bare-root or balled has no pot to go by, and Minnesota gives no other amount for a shrub. So there the calculator keeps the tree rule by the thickest stem, which is its own reading. Kansas State's bulletin MF2800 gives a tree up to 2 inches about 10 gallons a week after the first month, a higher figure; the sources disagree, and the calculator follows Minnesota. Every form of stock follows that schedule, bare-root saplings included. On the weekly schedule a soaking never removes the week's one watering: within three days of it the calculator says to check the soil first, and older rain changes nothing. Minnesota's table starts at a 1-inch tree. Below about two thirds of an inch the calculator still counts a full year, so the first summer is always covered. That floor is its own reading of Colorado State Extension, which gives a tree under 2 inches "one to two or more seasons". Colorado State adds that a warmer area may take less time and a cooler one longer. Kansas State's bulletin waters a container-grown or balled tree "one to two times a week during the first month after planting", the fallback for anyone who cannot water every day. For a tree of 3 inches or more, Colorado State Extension waters daily for four to six weeks, where the calculator keeps Minnesota's two.

Colorado State Extension's schedule for newly planted trees and shrubs is for the growing season. For winter it says: "Water once or twice a month in winter if there has not been adequate moisture and the ground is not frozen. Start in the morning on a day when the high will be over 40° F." The calculator takes December to February as winter, past the first two weeks after planting, and gives each winter watering Minnesota's full dose. Kansas State waters a deciduous tree until its leaves fall and an evergreen until the soil freezes. University of Maryland Extension gives an evergreen a deep watering in the fall before the ground freezes if it has been dry. Where the ground does not freeze, the calculator gives Maryland's rule for the first two years after planting. That rule is to "check the soil moisture at least once a week and water if the soil feels dry at 6 inches". Minnesota gives no amount for an established tree. For a dry spell after establishment the calculator takes Colorado State Extension's: "1-2 inches of water every two weeks during the growing season (approximately 10 gallons per inch of trunk diameter)", given at the dripline. No source gives a figure for an established shrub. A shrub gets University of Maryland Extension's rule for all trees and shrubs instead: water when the soil is dry about 6 inches down, and soak it that deep.

In a hot, windy week Colorado State Extension says to "apply the higher amount at the more frequent recommendation". University of Maryland Extension says to water in the morning: "Watering during the heat of the day increases the amount of water lost to evaporation by as much as 40%." Minnesota adds: "As roots grow and spread, the water volume will need to be increased." Tree roots grow about 18 inches a year in Minnesota, it says, so the ring you water widens with them. Minnesota gives no figure for the extra water, so the calculator takes Kansas State's soaking of the wider ring "to a depth of 8 to 12 inches". The checks about 6 inches down are University of Maryland Extension's, as is mulch that "reduces water loss through evaporation" at 2 to 3 inches thick. Maryland measures a sprinkler with a tin can, an inch of water in it being "equivalent to an inch of rain"; set out in the open, the same can measures the rain. Kansas State warns that mulch against the lower bark "can keep bark wet, contributing to a canker infection or decay". The cups and quarts are those of the National Institute of Standards and Technology, which puts 4 quarts or 16 cups in a gallon. The way to time a hose is Iowa State Extension's: find how long it takes to fill a bucket of known size at the flow you water with.

The soil setting follows the direction the extension services share rather than any one schedule, since only Kansas State gives one for a new tree, and only for sand. University of Maryland Extension writes "Clay soil drains slowly, and porous sandy soil drains quickly", and Nebraska Extension "Deep, infrequent applications of water are recommended for clay soils". Illinois DNR writes "Trees in sandy soils may need shorter and more frequent watering regimes", and Iowa State Extension "Sand soils dry out faster than clay soils". Colorado State Extension warns that too much water in one session waterlogs a planting hole in clay. Kansas State's rule is "On sandy soil, split the 10-gallon application into two 5-gallon applications three to four days apart", which is the calculator's rule for sand after week 12. Don Horneck, an agronomist at Oregon State University's Hermiston research and extension center, put the sand rule in figures for OSU Extension in 2012. He set fine soil at four inches every eight days. On sand: "With sandy soil, you'd still use four inches, but you'd have to apply it one inch at a time, every other day over eight days". The page has since left OSU's site; it is read from the Internet Archive's 2023 copy. On sand the calculator halves the dose and about doubles the frequency after the first two weeks. On clay it keeps the dose and stretches the gap to every 3 to 4 days, then every 7 to 10 days, with a look at the soil first. Silt is treated as loam, which none of the sources schedules apart. Apart from sand after week 12, the sizes of those changes are the calculator's own reading of that guidance.

It is a starting point, not a prescription. The whole first year is in Transplanting young trees: timing, water and protection, and the planting mistakes no amount of water fixes are in Ten planting mistakes that quietly kill trees. The years after the first, winter included, are in A year-by-year care calendar for a newly planted tree.