Tree watering calculator
The calculator estimates the dose and frequency for a young tree and the weekly amount per square metre of permeable surface for a mature one, based on climate, soil, temperature, rainfall and wind. Below are the rules that apply whatever the number.
How much should you water your tree?
For young trees we calculate the dose per watering and the frequency; for mature trees, the weekly amount per square metre of permeable surface beneath the crown (SLIDE method, ANSI/ASABE S623). The result is a range; the reasons are explained below.
Four stages, four regimes
Year 1: the aim is to overcome transplant shock. Give 6.5–10 L per centimetre of trunk diameter, twice a week in hot weather, keeping the soil around the root ball moist. Year 2: roots leave the pit, so water less often, but more generously and wider. Years 3–5: deliberately lengthen the intervals. Mature tree: only in prolonged drought, a weekly amount per m² of permeable surface within the crown zone.
Mature trees are more often over-watered
A healthy tree older than a few years finds water on its own and tolerates dry soil for weeks without harm. Constantly wet soil starves the root zone of oxygen and favours decay. Water it only during prolonged drought, or as recommended by a certified arborist after an inspection, for example following construction work or root damage.
Rarely and generously, not often and little
Small amounts wet only the surface and keep roots shallow, where they are the first to suffer in drought. Generous, less frequent watering drives roots deeper. Water at the crown edge, where the absorbing fine roots are; next to the trunk are conducting roots that do not absorb. Water in the morning or evening; if the tree has a watering pipe, pour half into the pipe and half on the surface.
Winter drought: the most underrated cause of decline
Evergreens and conifers lose water through needles and leaves in winter too. If the soil is dry or frozen and a cold, dry wind blows, the tree cannot replace the loss and physiological drought sets in. The damage is usually noticed only in spring, when it is irreversible. Water on days above 4 °C when the soil is not frozen, in the morning and slowly.
Compacted soil isn't only an urban problem
Soil compacts wherever it is regularly loaded: a car park by a village church, a field track, a machinery turning area, where livestock gather or people walk in the shade. Compacted soil has no pores for water to infiltrate or roots to breathe, so water runs off the surface instead of reaching the roots. Water compacted soil slowly and in several passes; the permanent fix is soil decompaction, breaking up compacted subsoil layers and protecting the root zone from further trampling.
Watering is only first aid
The permanent solution is good-quality space for root development: soil decompaction and breaking up compacted subsoil layers, soil aeration, stormwater capture systems beneath the pavement, a mulch layer that does not touch the trunk, mycorrhiza, and species that tolerate drought on that site. Watering only buys time until that is done.
The calculation is indicative and does not replace professional assessment. For the first three years it uses a dose by trunk diameter (6.5–10 L per cm) with a frequency adjusted to evapotranspiration, consistent with Arboricultural Association guidance and municipal planting guides; for mature trees the SLIDE method (ANSI/ASABE S623) with a plant factor of 0.5, applied to the permeable surface within the crown projection. Reference evapotranspiration is estimated from temperature, a rough approximation.
A note on Croatian conditions: Croatia has unusually complex and varied climatic conditions, with continental, mountain and Mediterranean climates within a small area and large differences in rainfall, wind and soil even within one city. No general calculator can therefore replace an on-site assessment. We particularly note that winter watering of evergreens and conifers may be necessary even in continental Croatia, during dry, windy spells without snow cover. For a site-specific assessment, soil moisture measurement and watering plan, contact us.
Questions about watering
How much water does a young tree need?
As a guide, 6.5–10 litres per centimetre of trunk diameter per watering. A tree of 8 cm diameter in its first year, at temperatures around 28 °C and without rain, needs about 50–80 litres twice a week. More often in greater heat, wind or on sandy soil; less often after heavy rain.
Does a mature tree need watering?
Only during prolonged drought, or as recommended by a certified arborist after an inspection, for example following construction work or root damage. The weekly amount is then calculated per square metre of permeable surface within the crown projection: in summer usually about 10–20 litres per m² per week, in one or two generous waterings. Mature trees suffer more often from over-watering than from drought.
Why water conifers and evergreens in winter?
Because they lose water through needles and leaves in winter too. When the soil is dry or frozen and a dry wind blows, the tree cannot make up the loss and winter (physiological) drought sets in; the damage shows only in spring. Water by day, when the temperature is above 4 °C and the soil is not frozen.
Let's talk about your trees
We work with cities, municipalities, public institutions, designers and owners of valuable trees. For a quote, send us the basics: which tree or planting it concerns, where it is and what worries you.
How a quote comes about
Price depends on the number of trees, the methods required and the depth of documentation, so we do not publish it in advance. After an introductory call and basic site details you receive a written quote with a clear price and timeline. For public-sector clients we prepare documentation in tender-ready form.
ARBORING j.d.o.o.
Matije Gupca 6, HR-10450 Jastrebarsko
+385 98 411 431
fran@arboring.hr