Calculating Sun Angles for North-Side Planting Beds

In Zone 7a, the north side of the house receives dramatically different sun exposure between winter and summer. Knowing the exact solar altitude lets you predict shade patterns for plant selection.

Two Reliable Tools

1. NASA Sun Angle Calculator: Explains the geometry of seasonal sun angles relative to latitude.
2. SusDesign Sun Angle Tool: Enter your latitude/longitude to get precise solar altitude and azimuth for any date/time.

Quick Field Method

On December 21 (winter solstice) and June 21 (summer solstice) at solar noon, drive a stake at the roof eave line and measure the shadow length. The angle = arctan(eave height / shadow length). Project that angle to the ground to map the shade line.

Planting for the Resulting Shade

North-side beds in Zone 7a are typically full shade in winter and part shade (2–4 hrs morning/evening sun) in summer. Excellent choices:

• Foliage perennials: Hosta, Heuchera, Ferns (Autumn, Japanese Painted), Brunnera, Hakone Grass.
• Flowering perennials: Astilbe, Bleeding Heart, Hellebore, Toad Lily, Hardy Begonia.
• Shrubs: Fatsia, Aucuba, Mahonia, Hydrangea quercifolia, Rhododendron (with amended soil).

See Colorado State’s shade garden guide for more lists.