What’s Full Sun? & Spraying Roses With A Herbicide

Question:

This may be a silly question, but when a plant label or gardening book says full sun, does this mean that the plant needs direct sun for the whole day, or will it be okay if it gets shade in the late afternoon?

Answer:

  • No, this is a very legitimate question that's not asked very often. Full sun is defined as any plant that requires six hours or more of direct, unfiltered sunlight per day. The sun exposure is not a year-round measurement but from mid-March through October. Another way of thinking of this is when Daylight Saving Times is in effect.
  • It's also important to realize that the information on plant labels and gardening books are not tailored to your specific neighborhood. Instead, they're designed for a region that may include several states. The USDA Hardy Map or the Sunset Western Garden Book Climate Zones are the primary resources. Shade in the late afternoon should not be a problem for sun-loving plants. A 'shade loving' plant is any plant that requires filtered sun with less than three hours of direct sunlight per day but during the heat o
  • If the day. Full shade does not mean void of any sunlight. There aren't many plants, except mushrooms, that can survive in the dark. In addition, there is another very broad group of plants that are listed for 'sun or part shade. These plants will need some relief from the intense late afternoon sun, either from shade provided by a nearby tree, other plantings, a building, or other means. It would be best if you kept in mind that the day's hottest temperature occurs in the mid to late afternoon.
  • There are a wide variety of microclimates in Alameda and Contra Costa Counties. Identical plants can tolerate afternoon sun in one location and burn up in another. For example, Azaleas require morning sun and afternoon shade along the 680 corridor, but will grow in the full day sun in Alameda. Thus, measuring the sun exposure for plants is not an exact science. This has led to a  plethora of "sun to part shade" labels that are in gardening books and on plant tags. I'm surprised to see Coleus, Japanese Maples, Fibrous Begonias, Impatiens and, other so so-called had shade-loving plants thriving in the afternoon sun on the hottest days.
  • The nursery professional at your favorite garden center is an excellent resource to help sort things out. 

Question:

What happens if you accidentally spray your roses with weed killer that I thought was deer repellent, then desperately hose the leaves off with water. Have I killed my roses? Or will they recuperate and get back to normal?  

Answer:

  • I don’t know what’s going to happen. Herbicides will enter plants through the leaves, roots, or both. Washing off the leaves is helpful, but the roots could absorb the contaminated water and cause additional damage depending on the herbicide. Without knowing the herbicide name, it’s impossible to predict what will happen.