Climate Zone; Gardening, Drought Resistant Plants.
Weather Statistics; UV Index
Climate Zone, General
Hacienda Heights resides climatologically in an area known as the "Mediterranean" climate because the land that borders the Mediterranean Sea is a type locality for this climate. This Dry Summer Subtropical climate is punctuated by wet winter/dry summer seasonality of precipitation. Summer drought places a great deal of stress on the local vegetation, as well heavy wet rains in the winter can cause mud slides in the hills (especially in “El Niño” winters).
Temperatures in the Mediterranean climate is rarely extreme, with winter freezes rare at the altitude that Hacienda Heights resides at (400 to 1300 feet), however the San Gabriel Mountains on the north side of the San Gabriel Valley rise up to 10,000 feet (3048 m) and average much more rain and can collect snowfalls over 200 inches.
Summer temperatures are also not too extreme, however they can be long with summer-like temperatures (80-90 F) occasionally reached during Santa Ana wind events during winter months.
Hacienda Heights averages 292 days per year with full daylight lighting.
Climate Zones Specific; For Planting/Gardening:
Hacienda Heights occupies two slightly different climate zones (as per planting concerns).
Most of Hacienda Heights falls into what is considered Western US climate zone 21 which is the hills and much of the rising terrain leading up to the Puente Hills (also known as the Whittier Hills).
The remaining terrain which is primarily along the Pomona Freeway (State Route 60) is considered Western US climate zone 20. This zone (20) occupies most of the lower terrain of the San Gabriel Valley (which is the valley Hacienda Heights is located in).
The world famous Los Angeles County Arboretum in Arcadia (also in the San Gabriel Valley) is also located in zone 20 (bordering zone 21), so the vast choice of plants is obvious here.
The rising terrain (known as zone 21) is excellent for growing citrus (this used to be the Citrus belt prior to the 1960s). Ocean influence is mild, but enough to limit some extreme temperatures for both winter or summer, however winter chills are pronounced just enough to allow for some plants such as lilacs that require some mild but pronounced chill for dormancy, although generally not enough for more chill such as Apples or Cherries.
Generally the rising terrain of most of Hacienda Height’s zone 21 is an area of mild ocean influence that interplays with dry interior air, often under stratus clouds in the early morning hours from ocean influence in late spring and even in the summer. One difference from the low terrain of zone 20 along the Pomona (Route 60) Freeway/Gale Ave. is that some tender plants (such as Cyclamen persicum & Dwarf Cavendish) that cannot tolerate the occasional winter frosts that can settle in zone 20 will do better the rising terrain of most of Hacienda Heights. Generally Avocados (pictured above left) do better in the rising terrain of most of Hacienda Heights as compared to the low points of the San Gabriel Valley.
Drought Resistant Plants for Zones 20-21 (not a complete list):
• Brahea Armata (Blue Hesper Palm)
• Edible Fig
• Lyonothamnus Floribundus (Catalina Ironwood)
• Walnut (depending upon species)
• Olea europaea (Olive Tree)
• Romneya coulteri (Matilija Poppy)
• Red Flowered Crassula falcata
• Mimulus (Monkey Flowers)
• Limonium perezii (Sea Lavender)
• Iris tenax (Pacific Coat Iris)
• Kniphofia uvaria (Torch Lily)
Historic Temperature & Precipitation Averages for Hacienda Heights
Other Weather/Climate Statistics:
• Average UV Index: 5.42, with a high of 9 in June/July and a low of 2 in Nov.-Jan.
What is the UV Index? The UV Index is a daily forecast of the UVA & UVB (as opposed to the UVC Radiation used for home air purifiers and UV Sterilizers, provided by a UV-C Bulb in these units) radiation levels people might experience, UVC is blocked by the ozone layer and never reaches the surface. The Index predicts the next day's levels on a 0 to 10+ scale, helping people determine appropriate sun protection behaviors.
*0 to 2 Minimal
*3 to 4 Low
*5 to 6 Moderate
*7 to 9 High
*10+ Very High
Or see this informative site about the use of UVC: UV Sterilization
• Last Snowfall; the last measurable snowfall in Hacienda Heights was in January 1949 with several inches falling in “The Heights” (the exact amount is not established since Hacienda Heights did not have official record keeping and the amount varied considerably since Hacienda Heights has considerably varied terrain).
Climate; Sunset New Western Garden Book