California’s anticipated winter season breaks the long dry spell of summer. Rain fall varies greatly throughout the state with the northern and coastal sides typically receiving more showers than the south. Regional climates can vary drastically with Northern California typically receiving between 15 to 50 inches of rain while parts of Southern California can receive between 8 to 15 inches. In addition to these varied amounts of water, rains can begin in different months depending on the region.
For farmers who rely on the winter rains for their cover crops’ water requirements this can make timing the planting difficult. Like all crops, cover crops require water to grow, however since they’re usually not being grown for harvest, they can often go with very little water. The most important time for cover crops to have water is during germination. Because of this, farmers need to time planting their cover crop with the rains if they won’t be irrigating it themselves. This can greatly vary the planting date of the crop. In more northern areas cover crops can be planted as early as September or October depending on the start of the rainy season. More southern locations may plant their cover crops in early November to as late as December. Even drier places may be looking at planting their cover crop into the early spring, although our Seeds for Bees program encourages every effort to plant in fall so that cover crops are blooming when bees arrive the following winter for almond pollination.
Knowing the climate and weather conditions of the region can help the grower to select a cover crop and the planting date. Northern farmers can more easily use cover crops with greater water requirements, like many legume species, than those in drier areas who will be using more drought tolerant species like brassicas and grass-based mixes. However, this can fluctuate depending on available irrigation water and whether the system can reach the center of the orchard alleys.
Many growers wait to plant their cover crop seed till just a few days before or after a large rain event. Cover crop seed can be seeded up to 2 weeks before a rain, after this time germination rates may begin to decline. Farmers using a seed drill with hard or compacted soils may want to wait until the ground is workable after a rain to allow the drill to better penetrate the soil. For many cover crop mixes about half an acre inch of water is enough to promote good germination and establishment.
"The most important time for cover crops to have water is during germination."
Planting too late can also be detrimental to the total possible benefits which could have been gained from the cover crop. Missed rains is missed growth, for species like legumes that could mean less total fixed nitrogen than what could have been available with an earlier planting date.
Cover crops have their own effect on rain on the farm. Bare soil is more vulnerable to erosion and crusting due to the impact of rain fall. This crusting can be especially detrimental to row crops where crusts can potentially prevent seedlings from emerging. Over time soil crusting can promote water runoff and reduce water infiltration into the soil. Cover crops and resident vegetation can protect the soil from the brunt of the rain while the roots can hold soil together. Cover crop roots improve soil conditions by creating channels for water to infiltrate, reducing ponding and water runoff. This keeps precious rain fall on the farm and not running down the street drain.
"Cover crop roots improve soil conditions by creating channels for water to infiltrate, reducing ponding and water runoff. This keeps precious rain fall on the farm and not running down the street drain."
Increased infiltration can prove vital in orchards during bloom, when spring fungicide sprays can mean the difference between a healthy crop or loosing blossoms to blight. Depending on soil type and the cover crop, farmers can reenter fields days if not weeks earlier with cover crops than bare soils. In especially wet springs this can mean that the farmer can reenter their field to conduct sprays much sooner than in bare orchards before a sequential rain.
It’s especially important to keep blooming cover crops in mind when scheduling a spray in the orchard. Many pesticides can be toxic to honeybees, especially if they are and they can be sprayed while bees are foraging on the farm. Even if the pesticide is labelled as nontoxic to honeybees, getting t their wings wet can ground them for extended periods of time, making them vulnerable. This results in reduced productivity and may lead to lower pollination rates. The Almond Board of California recommends spraying in the late afternoon to evening when bees aren’t present. Additionally, the Almond Board of California has found that including insecticides in spring bloom sprays can be detrimental to bees and many common insect pests of almonds are not present at this time. Utilizing chemicals to control pests when they are not present will increase costs and may require additional sprays when pests emerge later in the year.
 Climate of California, Western Regional Climate Center. Retrieved from: WRCC: California Climate (dri.edu)
 Honey Bee Best Management Practices for Almonds: A guide for almond growers by the Almond Board of California
Seeds for Bees Manager