Treety
TR/01Treety

01 / Overview / Street trees / Los Angeles

New street trees die of thirst.Grown ones lift the sidewalk.

Treety is a buried rain box with sand wicks. It catches curb runoff all winter and feeds it to a young tree through the dry season, only as fast as the soil dries. The water arrives 12–18 inches down on the curb side, so that is where the roots grow.

Prototype images coming soon

System
Treety street-tree kit
Source
Curb runoff from about 500 sq ft of street, about 280 gal per inch of rain
Storage
About 390 gal, 12–36 in. below grade
Delivery
6 sand wicks, outlets 14 in. deep
Power
None. Gravity in, capillary action out
Install
Parkway only; the existing sidewalk stays. Optional add-on when a sidewalk is being rebuilt
Upkeep
0–2 summer refills, down from 26–52 waterings
Status
Bench prototype in build
$1.4B1

LA's 30-year sidewalk repair commitment under the Willits settlement.

92%2

of downtown LA's rain falls November through April. Trees need water most from May to October.

15 gal3

a week is the usual dry-season watering for a new tree, for its first three years.

85%4

of a tree's roots grow in the top 18 inches of soil.

02Problem / new plantings / LA parkways

Two failures with one cause: water in the wrong place.

Thirst

A new street tree needs about 15 gallons a week through the May–October dry season, for three years.3 LA County asks residents to water new parkway trees about twice a week in warm months.5 That is 26 to 52 visits a summer per tree, by a resident, a volunteer, or a watering truck. When the visits stop, young trees die.

Heave

Water poured at the surface keeps roots shallow. Moisture also condenses under concrete, which makes the soil just under the slab the best spot around. Roots there thicken a little every year and push the slab up.

Treety moves the water to where we want the roots: deep, on the curb side, and only when the soil needs it.

Watering todayTreety
WaterTap water, hauled by truck or hoseWinter street runoff, stored on site
Lands atThe surface12–18 in. down, curb side
Summer visits26–52 per tree0–2 refills
OverwateringPossibleWicks stop once the soil is damp
RootsStay shallow, near the slabGrow down, away from the walk
03Section / along the parkway / depths to scale

Winter fills it. Summer drains it. The soil sets the pace.

Winter
Summer use
Treety long section along the parkway. Tap a numbered part for details. 390 gal 0″ 12″ 17″ 36″ 48″ grade
Depths to scale. Lengths shortened. Full box 2.5 × 14 ftTap a number for details · swipe sideways for the rest
Gallons in the box each week of the year, with weekly rain
DateAug 5
In the box0gal
Water surface0in. deep
Wick climb0in.
Refills / yr0
Overflow / yr0gal

How to read it

Tap any number for what that part does and its specs. Blue is stored water. It can't rise above the standpipe rim at 17 in.; anything more drops down the standpipe into the gravel trench. The tan lines are sand wicks: each starts in the reserve at the box floor and rises to an outlet at 14 in., inside the green sweet spot.

As the box drains, the wick climb gets longer: 3 in. when full, about 21 in. near empty. That climb is exactly what the prototype tests.

The year runs from October 1 and uses downtown LA's average monthly rain.2 About 280 gallons reach the box per inch of rain, from roughly 500 sq ft of street. A tan triangle on the chart marks a 150-gallon crew refill, triggered when the box falls to its 25-gallon reserve.

Even a dry winter fills the box, because about 1.4 in. of rain fills it from empty. What decides refills is how long and hot the dry season runs.

Full parts list and specs
#PartDepthSpec
04Mechanism / five moves / no pumps, no power

Gravity brings the water in. The soil decides when it comes out.

  1. 1Step 1 / Capture

    Street runoff fills the box

    Gutter water flows through a curb opening onto a grate that catches trash and leaves. Below it, three layers of washed rock, coarse to fine, strip out grit. A flap valve at the box wall lets the clean water in and shuts behind it. About 280 gallons arrive per inch of rain.

    Grate → 1½ in. rock → ¾ in. rock → ⅜ in. pea gravel → flap valve → box

  2. 2Step 2 / Store

    A box the tree can't flood

    Plastic storage crates in a welded liner, 12–36 in. below grade. An adjustable standpipe with its rim at 17 in. caps the water level and sends the extra to a gravel trench, where it soaks down into deep soil. Above the rim is surge space for storms. Flap valves on the inlet and overflow, a gasketed lid, and a screened vent seal it against mosquitoes, as California's mosquito guidance asks for anything that holds water longer than 72 hours.6

    2.5 × 14 ft · overflow 17 in. · about 390 gal · dig 3.3 ft (4 ft at the trench)

  3. 3Step 3 / Release

    Water moves only when the soil pulls

    Six U-shaped sand wicks start in the reserve water at the box floor and rise to outlets 14 in. down. Capillary action lifts water as the soil around each outlet dries, and slows to nothing when it is damp. The outlets sit above the overflow line, so the wicks can't siphon the box empty. The fill is a silt-rich sandy mix: in lab columns, plain fine sand lifted water only about 8 in., while silt lifted it about 5 ft.7

    Tree needs 8–11 L/day · estimate about 3 L/day per 4 in. wick · 6 wicks

  4. 4Step 4 / Steer

    Roots grow where the soil is best

    Roots don't hunt for water. The ones that land in damp, airy soil grow and thicken fastest. Treety puts that soil at 10–20 in. on the curb side, and a root barrier runs along the sidewalk edge of the parkway. The sidewalk itself has two options. Keep it: no sidewalk work at all, and the barrier and sweet spot do the steering. Or, where a city is replacing the walk anyway, add a gravel layer under the new slab to break up the damp film that draws roots up; in a long-term field comparison, a barrier and a gravel layer were among the treatments with the least lifting.8 Structural soil down to 36 in. under the new walk then gives roots room to cross deep, toward the yard.9

    Sidewalk

    No sidewalk work. The barrier goes in from the parkway side, and the curb-side sweet spot gives roots a better place to go. Less room for roots, so plant a smaller-canopy tree.

    Across the parkway: how Treety steers roots away from the sidewalk Cross-section from the yard to the street, depths to scale. A root barrier runs down the sidewalk edge of the parkway to 24 inches. The tree's main roots grow toward a damp sweet spot on the curb side, 10 to 20 inches deep, where the wick outlets are, and a shallow root heading for the sidewalk stops at the barrier. With the existing sidewalk kept, the old base under the slab is untouched and deep roots grow down within the parkway. With a rebuilt sidewalk, a gravel layer sits under the new slab with structural soil down to 36 inches, and a deep root crosses under the walk at depth. 0″ 12″ 24″ 36″ YARD SIDEWALK PARKWAY CURB STREET Root barrier Existing base, untouched Roots go down Gravel layer Structural soil to 36″ Roots cross deep Sweet spot
    Across the parkway. Depths to scale, widths shortenedThe storage box runs along the curb side, just out of this cut

    Barrier on the sidewalk side only. Never a ring around the tree.

  5. 5Step 5 / Long term

    Then it keeps working

    Roots can't get into the box: the bottom of each U stays underwater, and roots stop at soaked, airless soil. In years 3–5 a crew slides the standpipe down a few inches at a time, so more winter water drains to the gravel trench and deep soil, and the roots follow it down. After that, the tree won't necessarily need the water, but the box stays in the ground for good: as drought backup that keeps roots on the curb side, or switched to recharge mode, sending most of each storm down toward groundwater.

    Each inch the standpipe drops moves about 20 gal from storage to the deep soil

05Long term / depth ladder / year 0 and on

Stays in the ground. Keeps working.

Treety is permanent. It trains the roots deep over the first five years, and after that an established tree may not need its water at all. In most of LA, groundwater sits far below a street tree's roots, so the tree lives mainly on winter rain held in deep, roomy soil.10 The box stays either way, and the city picks how it works from year 5 on.

PhaseYearsWhat the box doesStandpipe rimHuman work
Establish0–2Wicks keep 12–18 in. moist17 in.0–2 summer refills
Train deep3–5More winter water drains to the gravel trench and deep soil (28–48 in.); shallow soil dries between storms20 → 23 in.Refills only in heat waves
Backup5+Wicks stay in. The curb-side sweet spot stays the tree's best soil, so roots stay off the walk, and the box carries the tree through droughts and heat waves23 in., raised in a droughtRinse the rock filter, vacuum silt, swap clogged wick cartridges
Recharge5+Keeps about 120 gal in reserve and sends the rest of each storm down through the gravel trench: about 3,000 gal a year in a typical year, 1,300 in a dry oneAbout 30 in.Rinse the rock filter and vacuum silt once a year

Sensors at the outlets and in the box tell a crew when to refill and when a tree is ready to move down a rung. Watering deeply and infrequently is what builds a deep, drought-tough root system.11

06Prototype / Rig A / wick bench

Prototype images coming soon.

Image coming soonRig A, full bench
Four wick tubes, reservoirs, and trays on scales.
Image coming soonDye front at 24 in.
Time-lapse of water climbing a clear tube.
Image coming soonFirst flow chart
Grams per day moved by each fill, at each climb.

What we're building

Rig A tests the one number we couldn't find published for this use: how much water a sand wick can lift 24 inches, day after day.

  • Four 2 in. PVC tubes, about 30 in. long, each packed with a different fill: fine sand; 85/15 sand and silica flour; 70/30; sandy loam. One tube is clear so the rising water shows.
  • Each tube stands in a constant-level reservoir (an inverted 2-liter bottle feeding a small tub) and feeds a tray of sandy loam above it.
  • A box fan dries the trays the way a summer dries a parkway. A fifth tray holds plain water, to measure how fast the fan dries things.
  • Each reservoir sits on a kitchen scale, so grams lost per day equals water the wick moved. We test climbs of 24, 18, 12, and 6 in., hardest first.
Pass mark 1.3–1.8 L/day

per field wick, so that six wicks together cover a young tree's 8–11 liters a day. A 2 in. bench tube has about a quarter of the area of a 4 in. field wick, so it passes at about 0.35–0.5 L/day.

The winning fill goes into the full design and into our root simulation. Photos, the time-lapse, and the first flow data will post here as the bench runs.

07Model / data / limits

What we know, and what we're testing.

Proven on its own
  • Deep, infrequent watering grows deeper roots.
  • A root barrier or a gravel layer under the walk had the least sidewalk lifting in a long-term field comparison.
  • Wicking beds keep soil moist from a reservoir below.
  • Curb-fed tree pits capture and clean street runoff.
Still open
  • All of it together in a real LA parkway over several summers.
  • Wick flow at a 24 in. climb. Our 3 L/day estimate assumes the fill stays saturated; Rig A measures it.
  • How fast roots fill the wick legs. Wicks are pull-out cartridges for that reason.
  • Structural soil on its own. In that same comparison it had the most lifting (the differences weren't statistically significant), so Treety only uses it with the barrier and gravel layer.
  • Keeping the existing sidewalk: how well the barrier and the curb-side sweet spot hold roots without a gravel break under the old slab.
  • Approvals: a city tree permit, a public works standard plan, and vector control sign-off for the sealed box.
What the year model leaves out
  • Storm timing. Rain is spread evenly through each month, and the first 0.25 in. a month is assumed to wet the pavement without reaching the box.
  • Heat waves. Tree use is fixed: 15 or 20 gal/week May–October, 5 gal/week November–April.
  • Water held in the surrounding soil, an extra buffer on top of the box.
  • Site limits. The gravel trench needs soil that absorbs at least 0.3 in./hr, must sit 10 ft from foundations and property lines, and needs its bottom at least 10 ft above groundwater. Every site starts with a DigAlert utility check.
08Pilot / 2–3 trees / one dry season

Host a pilot tree.

We're looking for a city, a planting nonprofit, or a developer to host two or three Treety trees and monitor them through one dry season, May to October. That summer is the real proof.

CAL FIRE's Urban & Community Forestry grants have funded tree planting, establishment care, and site improvements like bioswales, so Treety can be written into a city or nonprofit's application when the next round opens.12

Contact Miles Silverman Team lead, Treety · Civil Engineering Student, USC Viterbi
milessil@usc.edu
09Sources
  1. TreePeople, on the Willits settlement: $1.4 billion over 30 years for LA sidewalk repair. treepeople.org
  2. National Weather Service Los Angeles, 1991–2020 climate normals, downtown LA (14.25 in./yr). weather.gov
  3. Alameda County, new street tree care: 15 gallons once a week, May–October, for the first 3 years. acgov.org
  4. Colorado State Forest Service: about 85% of a tree's roots are in the top 18 inches. csfs.colostate.edu
  5. LA County Public Works, parkway tree care: water about twice a week in warm months for about 3 years. ladpw.org
  6. UC IPM, mosquitoes and stormwater structures: 72-hour rule, 2 mm openings, flap valves. ipm.ucanr.edu
  7. Capillary rise in sand and silt columns: about 20 cm in fine sand, about 155 cm in silt (ASA, CSSA, SSSA meeting paper). scisoc.confex.com
  8. Smiley, "Comparison of Methods to Reduce Sidewalk Damage from Tree Roots," Arboriculture & Urban Forestry, 2008. auf.isa-arbor.com
  9. Cornell Urban Horticulture Institute, Using CU-Structural Soil: at least 24 in. deep, preferably 36. Cornell guide (PDF)
  10. Minnesota Stormwater Manual, minimum soil volume for trees. stormwater.pca.state.mn.us
  11. University of Arizona Extension, watering trees deeply and infrequently. extension.arizona.edu
  12. CAL FIRE Urban and Community Forestry Grant Program (program description, past round). grants.ca.gov