Sighting the Garden - Sunlight and Siting the Garden

Cannabis plants need 5 to 6 hours of direct sunlight, preferably during midday, at minimum levels of 4,500 foot-candles (48,437.6 lux), to flower well and produce a good crop. Lower levels of light prolong harvest and lower both quality and yield. Cannabis requires the most intense sunlight during flowering. Receiving more hours of direct sunlight during flowering promotes thick, dense flower buds. Ideally cannabis should be planted in an open, level fi eld with no shade. But most often gardens are shaded by trees, houses, buildings, and so forth, and it is not possible for them to receive full sunlight all day long.

On the summer solstice (the longest day of the year), the angle of the sun at 40.3º north latitude* is 73.2º. On the winter solstice, the shortest day of the year, the angle of the sun at the same latitude is 26.2º. As the angle of the sun climbs in the sky, sunlight intensifies and lower shadows are cast from objects over gardens. In the fall when the angle of the sun drops in the sky, intensity diminishes and objects throw a longer shadow.

Measuring the path of the sun through the sky can be guesstimated by standing at planting sites and looking toward the sun. Hold your arm up and track the arc of the sun. Figure the sun will climb and drop in the sky, and guess about how much shadow it will throw. Or you could buy one of several applications such as the Sun Seeker for an iPhone or an Android phone that allows you to type in any date and see the path of the sun. I love this application!

*The angle of the sun changes in relation to latitude. In the USA, Eureka, California; Salt Lake City, Utah; and the border between Kansas and Nebraska, are all about 40.3º north latitude and Madrid, Spain is very close to the same latitude. Direct sunlight can heat foliage and cause plants to transpire excessive amounts of water in order to stay cool. Shade cloth stretched over plants will lower temperatures by blocking a percentage of the sunlight that hits foliage.

A natural breezeway is also formed between the shade cloth and plants, which helps to cool them even more. If shade cloth is not an option, give plants heavier doses of magnesium and calcium. See also “drought” in the Index. Scout garden sites in winter and try to visualize how trees will cast shadows during summer months, and ow plants will get 5 to 6 hours of midday sun. Use one of the many iPhone or Android phone apps that tell you exactly where the sun will be on specific dates. Remember that the sun takes a higher path in the late spring and summer. Six hours of direct midday sun per day is essential for acceptable growth.

More is better. South-facing gardens, hillsides, and terraces receive full sun all day long. See chapter 11, Greenhouses, for more information on hours of light per day for various climates. Outdoors, hours of daylight are short in spring and increase in length during summer. Daylight hours diminish in fall and winter. The shortest day of the year falls on or near December 21, and the longest day of the year falls on or near June 21. Note that at 40° north latitude, the maximum amount of sunlight is only 15.2 hours on June 21. If plants are grown in a greenhouse, supplemental light could be applied to increase production.

Special Planting Considerations

Little research has been done on cannabis and plants that produce allelotoxic chemicals.* Some plants are immune to these toxins, and others are not. These chemicals may not affect cannabis, or all varieties of cannabis. Nonetheless, avoid planting under trees or near bushes that produce allelotoxic chemicals, including: black cherry, cottonwoods, hackberry, junipers, sassafras, sugar maples, and walnut trees. Black walnut trees are the worst. *Allelotoxic chemicals are released by one plant that has an effect on another plant.

The release of allelotoxic chemicals is a survival mechanism that allows certain plants to compete with or kill other plants. The chemicals often inhibit seed germination, root development, or nutrient uptake. This is an excerpt from chapter 12 “Outdoors” from the Cannabis Encyclopedia (596 pages, 2,000+ color images, large A4 format) by Jorge Cervantes that is available everywhere in English. Spanish edition will be available January 2017. For more information please see Jorge´s website, www.marijuanagrowing.com. By Jorge Cervantes