How to Prevent Winter Weeds in Your Rocks

Preventing winter weeds in your rocks

In Arizona, there is no relief from the constant threat of weeds, even in the winter. While most of the country is covered in snow, our state is covered in weeds, so Arizona is still the better place to live, the weeds think so too.

Weed seeds, lying in wait below your rock-yard, start to germinate and sprout as the temperature begins to drop, in our fall and winter months.

Winter weeds you may see in your yard:

  • Silver-Sheath Knot-Week (Polygonum argyrocoaleon).
  • Spiny Sow-Thistle (Sonchus asper).
  • Nettle-Leaf (Goosefoot chenopodium murale). This is one of the few weeds that can be identified by scent, it has a strong unpleasant smell. It can grow up to 3 feet tall, growing from December through June.
  • Wild Oat (Avena fatua).
  • Shepherds-Purse (Capsella bursa-pastories)
  • London Rocket (Sisymbrium trio). Called a rocket because of how tall and quickly it grows, this weed contains yellow flowers and grows up to 36 inches! It loves our cooler weather but can continue menacing your rock yard all the way from December to May.
  • Prickly Lettuce (Lactuca serriola).

London Rocket, Sow Thistle, and Prickly Lettuce are three of the most common winter weeds, in the valley.

How to keep them out of your yard

Chances are, these weeds are already waiting in your rocks for an opportunity to sprout. Sadly, neither pulling them or spraying them with post-emergent herbicide or weed killer will be a long-term solution, you’ll be out on the rocks every few days pulling or spraying again, all season long. A post-emergent spray will kill the individual weeds you hit, but not the seeds.

For best results it is important to water in the pre-emergent so it can bind with the soil where the weeds germinate; otherwise, it remains on top of the rocks where UV exposure will break it down over time. An adequately watered pre-emergent (approx 1/4” of water or 15 minutes of sprinkler time) will bind to the first 1-2 inches of soil where the seeds germinate, creating a barrier that will kill the germinating seed before it breaks the surface.

Please Note

Pre-emergent and post-emergent sprays are not interchangeable, and you will waste a lot of time and money trying to prevent weeds with a post-emergent spray or kill weeds with a pre-emergent spray. The effective treatment utilizes a pre-emergent for long-term reduction and control of new growth and a post-emergent herbicide for spot treatments and maintenance.

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