Science to the Grower

Evaporation is the process by which water turns into vapor from a surface. After an irrigation or precipitation event, water evaporates from the growing media, soil, and wet plant surfaces. Conversely, transpiration refers to water traveling through a plant’s roots and vascular system and turning into vapor inside the leaf mesophyll, before leaving to the atmosphere through stomata.

In California nursery production, light is one of the most important environmental factors influencing crop timing, plant quality, and uniformity. While the state is known for high annual solar radiation, many greenhouse operations still experience periods, especially from late fall through early spring, when natural light is not sufficient to meet the needs of certain crops. Shorter day lengths, frequent coastal fog, and prolonged cloudy periods can significantly reduce Daily Light Integral (DLI), particularly in propagation and liner production systems. 

Nurseries supplying Brassica transplants face immense production challenges due to downy mildew, caused by the Oomycete pathogen Hyaloperonospora brassicae. Large-scale monoculture plantings at different growth stages, dense planting spacing, and overhead irrigation, consistently contribute to high downy mildew incidence and large quantities of downy mildew inoculum. Moreover, the cool climate and nighttime moisture of California’s Central Coast create optimal conditions for infection in outdoor nursery spaces and grower plantings.

As water scarcity and state regulations challenge California’s horticultural industry, many nurseries are turning to recycled runoff water as a primary or supplemental water source. While a “no-discharge” reality presents logistical hurdles, it also offers an opportunity to improve resource efficiency, however careful management must be taken not to spread chemical and biological contaminants throughout your property and into neighboring properties. 

The tools available for growing our plants include testing a variety of parameters including specific ion nutrient testing, pH, salts, crop height, pathogen analysis, leaf tissue testing, and substrate testing to name a few. One overshadowed parameter is the amount of light we give our crops. Tracking light levels is important, but there are various ways to measure light, each with different implications for understanding plant growth.

In this video we go over how to effectively scout for plant diseases in the nursery.  

The main steps include:

Recycled irrigation runoff water is a viable alternative for nursery and greenhouse production. However, it is likely to have plant pathogens present including: viruses, water molds, fungi, nematodes, and bacteria. To prevent plant pathogen spread, recycled irrigation water needs to be disinfected. Typical sanitation techniques include using chemicals (e.g. chlorine products or ozone), heat treatments, or ultraviolet light to kill pathogens.