Q&A: Rainwater Calculations, Weeds and Weed Cloth

Sheri and I just finished teaching the last of the San Diego Sustainable Landscape classes down in Lakeside. It’s a bittersweet moment – we love teaching that class, so it’s sad they are all over. But we have plans, so watch this space!

Meanwhile, people always have more questions, and we are really happy to answer!

Question:

Thanks again for the great class on Saturday. I have completely changed my design plans based on what we learned and am going to take the San Diego Sustainable Landscapes approach rather than the weed cloth/rock/DG approach.

 

One question:  Can we saw cut through a driveway to get the rain gutter runoff diverted to a new swale that we’ll build? We’ve calculated the amount of cubic feet of roof will generate but I can’t find a formula for how big the swale should be to accommodate that water. Is there some standard formula for that?

 

Thanks for any info you can provide and I look forward to my a beautiful, healthy yard that’s water conscious and sustainable.

Answer:

Yes, you can saw cut through the driveway to move water away from house into landscape. We did this for a workshop in City Heights back in June and used a local company called Cut N Core 

 

The calculation for the size of the swale is

 

the number of gallons divided by 7.48 = the number of cubic foot you need for the water

 

So, if its a 1″ rain event on 1000 square foot of roof, you can expect to capture 620 gallons

If we divide 620 gallons by 7.48 we get 82.88, call it 83 cubic foot.

You would be looking at an area that is roughly 10’x8′ or 9’x9′ or 40’x2′

Question:

I’m getting really skeptical comments from my family & friends about not using weed cloth. I’ve removed fescue grass, very healthy grass by the way with few weeds, but what’s to keep the grass/weeds from growing back if I’m not using weed cloth or DG?

 

My husband says we can work compost into the soil with the tractor (it an 8,000 sq ft area) but wouldn’t that only encourage every living thing to want to pop back up? He said he doesn’t want to go from mowing/edging every weekend to pulling weeds. Good question!

 

I’ve got him sold on the idea of catching our own water, now how do I convince him to keep the soil healthy by not compacting it?

Answer:

Weed cloth – if I could get a dollar for every installation of weed cloth that I’ve seen with weeds growing through it, I’d be rich! Sheri used weed cloth at her house- her gardener convinced her it was the right thing to do. 6-8 months later I came over and saw weeds growing right through it.

 

Weed cloth also stops oxygen and water from getting to the soil- key parts of OWL. And it collects blown dirt which allows weed seeds to root and grow. When you then try to pull them you end up pulling up the weed cloth with them. Finally, I used to use it when I was contracting and we could never keep it properly covered with mulch. There was always an edge or corner showing.

 

DG is ok for walkways but once you add stabilizers it becomes pretty impermeable. So much so that the new turf removal incentives will subtract any square footage covered with DG from the total of turf removed, meaning you won’t get credit for those areas.

 

The sheet mulch process has two parts to help stop weeds growing back. The first is the physical barrier of the cardboard or paper. This starves any weeds that do remain of light, so they die and decompose. The second is that soil that has some fungal activity (that 4″-6″ of mulch) is a natural deterrent to weeds. Weeds much prefer soil that is “new” with very little organic matter, just like annuals and veggies. In nature we would have to wait 100s of years for soil to go through this development, with weeds growing and dying many times over to build up the organic matter. The sheet mulching accelerates that process.

 

And talking of fungal activity – tilling soil breaks any fungal network up so we don’t recommend that. You will turn up weed seeds and push the soil development backwards towards the bacterially dominated end of the spectrum. This is why so many farmers are moving to ‘no till’ methods.

 

I hear the concerns about work in the new garden but all I can tell you is that my personal experience with my own yards, my experience with my clients’ yards and the studies (Santa Monica garden/garden) show that these sustainable landscapes take a fraction of the maintenance of a traditional lawn based landscape. There will be work up front but given time the self sustaining system will kick in and you will get to enjoy being in your yard rather than having to work in it.

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DIANE DOWNEY is a highly experienced landscape consultant, licensed landscape contractor, and landscape designer – she ran The Yard Fairy, an award-winning residential landscape design/build company for 10 years, holding a CA landscape contractor’s license (C-27).

SHERI MENELLI is an experienced permaculture design consultant, business owner, international public speaker and educator. She is a marketing and publicity consultant who has been in over 200 magazines and newspapers as well as made 5 TV appearances and been on over 50 radio shows. She’s worked in several industries with marketing and publicity including helping some of the top soil scientists in the world. She has been an educator, developing her own curricula for over 15 years.

Both Sheri and Diane blended their passion for landscaping and the environment with a background of teaching adults, and now regularly teach homeowner classes on rainwater capture, soil health, the use of native plants, turf removal, and efficient irrigation, both in the landscape, in the classroom and via one-to-one garden coaching sessions.

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