The Science

Light & Shade

Every plant has a light personality. Some crave full sun. Others thrive in the shadow of taller neighbours. Getting this right is one of the most important things you can do for a garden.

One tree casting three shadows throughout the day — morning shadow long to the west, noon shadow short below, afternoon shadow long to the east
Shadow length depends on the sun's altitude. We weight each hour by intensity — noon counts far more than dawn.

The Ellenberg Light Scale

In the 1970s, the German botanist Heinz Ellenberg did something remarkably practical. He walked through the forests, meadows, and wetlands of Central Europe and asked: how much light does this species actually live with?

Not how much it could tolerate in a lab. But how much light reached it in the wild, competing with every other plant for its spot. He scored each species from 1 to 9 — a Light number — based on brightness relative to an open field.

L = 1
Deep shade. <1% of open sunlight. Darkest forest floor — mosses, ferns.
L = 3
Shade. <5% of open sunlight. Woodland herbs under dense canopy.
L = 5
Semi-shade. ~10%+ of open sunlight. Woodland edges, hedgerows.
L = 7
Half-light. Down to ~30%. Mostly full sun, handles some shade.
L = 9
Full light. Never below 50%. Open grassland, basil, rosemary, lavender.

Even-numbered values fall between these anchors. "x" means indifferent — broad amplitude across light conditions.

Why This Matters

Ellenberg's values tell you not just what a plant can survive, but where it actually wins. This is the realized niche — where a species thrives after competition. Many shade-tolerant trees could grow in full sun, but they're outcompeted there.

For gardeners, this is exactly the right lens. Your garden is a community. A plant needs the right light niche to hold its own among neighbours.

A note on trees: Ellenberg scored trees based on their juveniles. A mature oak stands in full sun, but it spent its youth in shade. We distinguish shade-tolerant seedlings from sun-loving adults in our encyclopedia.

From Ellenberg to EIVE

Ellenberg's original values covered Central European plants. Over decades, botanists across Europe created regional systems. In 2023, 34 scientists harmonised 31 of these into EIVE — Ecological Indicator Values for Europe — covering 14,835 species with continuous-scale light values.

We use EIVE-L as our foundation. For species outside the dataset, we use machine-learning imputation from related species and shared traits.

EIVE 1.0 Dengler et al. 2023

How We Model Shade in Your Garden

Ellenberg measured light as a percentage of open sky. We simulate where shadows fall and estimate how much sunlight each spot receives.

1

Track the sun

For your exact latitude, we calculate the sun's position every 30 minutes — compass direction and altitude — for a representative day in each season.

2

Cast shadows

Each tree and structure shades the garden according to its height, width, density, and the sun's angle. Taller and wider objects block more sky, denser canopies cast darker shade, and low sun throws those shadows further across the garden.

3

Weight by intensity

Midday sun is far more intense than dawn. We weight each half-hour by sun altitude, so losing noon shade counts ~6× more than early morning.

4

Match the plant

The resulting percentage maps onto Ellenberg's scale. 60% of full sunlight suits a meadow species (L=7). 3% suits a woodland fern (L=2).

Four Practical Light Bands

Hill's literature categories are richer than most garden interfaces need. For practical placement, we use a four-band bridge: shade, semi-shade, half-light, and sun.

The cutpoints are chosen from Hill's anchor percentages at the dim, middle, and bright ends of the scale: shade plants mostly below 5% and seldom above 30%, semi-shade plants generally above 10%, and light-loving plants rarely below 40%. (Hill et al. 1999)

Practical Band Relative Light Linked Hill Classes Why This Split
☁ Shade< 10%L = 1–3Keeps the deep-shade end below Hill's >10% semi-shade anchor, while covering Hill's L3 shade plants.(Hill et al. 1999)
◒ Semi-shade10–30%L = 4–5Starts where Hill says semi-shade plants are generally above 10%, and ends at the 30% upper edge Hill still associates with shade.(Hill et al. 1999)
◐ Half-light30–40%L = 6–7A practical transition band between Hill's 30% shade ceiling and 40% light-loving floor.(Hill et al. 1999)
☀ Sun> 40%L = 8–9Starts where Hill says light-loving plants are rarely found below 40%; the brightest end of this band approaches full-light species.(Hill et al. 1999)

☁ Shade

Deep-shade through Hill's L3 shade plants: the darker end of the gradient.

◒ Semi-shade

The shadier middle, anchored by Hill's semi-shade plants with generally more than 10% light.

◐ Half-light

Bright partial shade to well-lit positions: our practical bridge for the L6–7 zone Hill describes verbally.

☀ Sun

Starts at Hill's 40% light-loving threshold; the brightest end approaches L9 full-light plants.

What We Can't Model

☁
Diffuse sky light. Even in shadow, plants get scattered light from the sky. We apply a 3% diffuse floor — no spot in your garden can fall below this — but real diffuse light varies with cloud cover and sky exposure.
🌲
Canopy filtering. Real tree crowns aren't solid. Light filters through as dappled patches. We model soft-edged projections but can't simulate every leaf.
🧱
Reflected light. Walls and paving bounce sunlight into nearby beds. In urban gardens this can meaningfully boost what plants receive.
🌍
Regional bias. Ellenberg's fieldwork was European. For tropical or Southern Hemisphere plants, our ML estimates are less certain.

Shadow modelling catches the big mistakes — a tomato behind a north-facing wall, a shade fern in full exposure. Getting the big calls right matters more than simulating every photon.

Further Reading

Ellenberg, H. et al. (1991). Zeigerwerte von Pflanzen in Mitteleuropa. Scripta Geobotanica 18: 1–248.

Ellenberg, H. & Leuschner, C. (2010). Vegetation Mitteleuropas mit den Alpen in ökologischer, dynamischer und historischer Sicht. Ed. 6. Ulmer, Stuttgart.

Chytrý, M., Tichý, L., Dřevojan, P., Sádlo, J. & Zelený, D. (2018). Ellenberg-type indicator values for the Czech flora. Preslia 90: 83–103.

Hill, M. O. et al. (1999). Ellenberg's indicator values for British plants. ECOFACT Vol. 2a. Institute of Terrestrial Ecology.

Dengler, J. et al. (2023). Ecological Indicator Values for Europe (EIVE) 1.0. J. Veg. Sci. 34: e13168.