California native plants are well adapted to our climate and can tolerate extended periods of heat and drought in their natural setting. Many natives experience a drought-induced dormancy in the summer. They simply maintain their size and shape, add very little to no new growth, and sometimes even lose a few leaves toward the end of the season. This is how they “tough it out”.
For natives to display such resilience during our long, hot, rainless season, they need to be well established with extensive, deep root systems. Branches shade the root zone and leaf litter or mulch will protect the topsoil from excessive drying. To have well-established landscape plants in the summer, you must plant in the fall, winter or spring. Summer is the most difficult season to install native plants in the landscape, but not an impossible time. We encourage our customers to wait until fall if at all possible.
If you are managing new plantings during the hot season, here are a few tips:
- Pre-irrigate the planting hole so there is adequate moisture around the root system.
- Plant at a depth such that the crown or base of the plant is slightly above the soil level, so that the water drains away from the stem. Planting too deeply will cause rot (see diagram in our “Planting Guide” on the website).
- Apply 1-2 inches organic mulch (no manure!) around the root zone of each plant. Keep mulch and excess soil well away from the stems and crown.
- Water by hose, drip or low volume sprinkler early morning. Avoid watering in the heat of the day or at night as this might cause branch die-back or root rot.
- Water only when the soil in the root zone (6-8”down) begins to dry out. Water thoroughly to soak the soil around the plant — deep enough to reach beyond the bottom of the planting hole.
- Avoid watering frequently with small amounts of water (high frequency, short duration).
- Apply water at a low flow with long durations to thoroughly soak the soil and allow vital oxygen to re-enter the root zone. Remember, mulch will preserve soil moisture between waterings.
- For best results, avoid using overhead irrigation for long durations (especially in the sun) because the prolonged leaf wetting during the dry season can promote disease.
Some species are especially difficult to handle in the summer, even for the most experienced native plant gardener. Fremontodendron, Penstemon, Romneya, Ribes, Dendromecon, Rhamnus, and Trichostema all do better with cool season installation. At inland sites Heteromeles, Rhus, Arctostaphylos some Ceanothus and most chaparral species are difficult to plant in the heat. The best approach is to postpone planting until fall. If you have to plant in summer, consider providing these sensitive types with temporary shade.
Use burlap or other mesh cloth supported by stakes on the sunny side of the plant to create a cooler micro-environment. Don’t drape the shade fabric over the plant, this will create even hotter conditions.
Don’t forget, everything starts getting a lot easier around October 15th. Stay cool!
* Make sure that the mulch you use is thoroughly composted. “Green” compost, (too fresh, not composted), will generate harmful excessive heat and compete for nitrogen as it begins to decompose around the new plants.