Ask a Landscape Architect
On the Bernardo Wills Architects Microsoft Teams site, we have channels dedicated to asking our colleagues tough questions. They could be related to current projects, COVID-19 design considerations, or personal projects. One our of staff members raised the following topic on our “Ask a Landscape Architect” channel last week:
“The former owners of my house ripped out the landscaping in front and put down gravel for parking. Now, it's a field of weeds. I've sprayed it twice with weed killer (Ortho and Roundup) and neither barely made a dent. So, now I'm mad and I bought straight up vegetation killer and those weeds days are numbered. My question is this: Once I conquer, what can I do to this area to keep the weeds from coming back next year? I want to put more rock down so it looks nice, but I don't think the previous owners did this right.”
James Davis, Landscape Architect and ISA Certified Arborist & Tree Risk Assessor, piped in with his answer:
Ideally, you would excavate down about 3-4" in the area(s) you want to install the rock. I typically don't advocate for fabrics in the landscape, but this type of situation is one exception. Lay down a thick, heavy-duty landscape weed barrier fabric like this one over the entire area(s) in question, overlapping seams by at least 12". Staple down the entire area with the least amount of landscape staples needed to hold it in place while you cover with gravel. In my experience, every staple exposes a hole in the fabric and therefore exposes soil where weeds can emerge. So the fewer staples the better! But you also don't want the fabric to fly away if the wind picks up before your rock is in place, so be mindful of both scenarios as you choose where to staple. If you decide to do a second layer of fabric, install this perpendicular to the first layer, still overlapping seams by at least 12", and staple down both layers together.
A good pre-emergent is important to install during this process. Preen Extended Control Preen Extended Control or Casoron are two products that will work. Install this in two applications per the manufacturer's specifications on the container: the first one should be applied directly to the soil right before installing your weed barrier fabric. This should help prevent any weed seeds that were already in the soil to germinate and emerge from underneath the fabric if conditions allow. The second application should be installed on top of the weed barrier fabric. This can be done after the gravel has been installed. After you have cleared the area, installed your first application of pre-emergent, and installed and stapled your weed fabric barrier, the next step is to install the crushed rock. This should be 5/8" - minus or 3/4"- minus (common in Idaho). The "minus" indicates the product will contain fines (fine particles) that will help the surface compact well, which is what you'll want if this is a parking area. Spread the rock product over the entire area and rake out with a metal tine rake to level. The gravel depth should be 3-4" thick.
Now, you can install the second application of pre-emergent on top of the gravel. It will work its way down towards the fabric layer and should help prevent any weed seeds to germinate that settle on top of the fabric. Pre-emergent has an expiration date... typically they will last between 6 months and a year. So early spring (before the weeds begin to appear) install an application of pre-emergent on top of the gravel area to prevent weeds for that year. If some weeds do germinate, pull them out immediately while they are small, before the roots have time to grow down deep enough to potentially damage the fabric. You can also choose to spot spray these emerging weeds with a product like Round Up which should kill them on contact within a few days. But once they die, still pull them out of the gravel. Even with the installation of a landscape weed barrier fabric, there will still be a small amount of maintenance associated. But this process should hopefully help eliminate a lot of work!
....or you could pave it...