Dear Patrick, I recently received your question about using weed barrier. I see that it was  sent September 1st and now it's the 8th.  I plan to send you information, so this email is just an introduction so that you know that your email did not get lost in the system.

Thanks for reaching out and I'll get down to business and send you a response.

Sincerely,

Hello again, Patrick! Let's see what we can do to try and understand the use and misuse of landscape fabric.

#1 - It's expensive. I don't know the amount of coverage you are describing in your email, but landscape fabric will greatly add to your cost of re-landscaping.

#2 - Weeds are opportunistic. The grow wherever the seed can find a place to germinate or the roots can find a place to rest. My mom even had bind weed growing under her foundation and crept across the carpet under her piano looking for light. Imagine that!

#3 - The name "weed barrier" is misleading. You will still find weeds germinating on top of the fabric where soil has blown in, creating a place for germination. In addition, perennial weeds that creep along, for instance bind weed, will continue to grow toward the light which will be along the edge of the fabric or where the fabric overlaps, where it will appear and continue to photosynthesize, increasing the root mass which in turn increases the shoot mass, etc., etc., etc. 

#4 - You might think that the fabric was the perfect solution for the first year or so, but after that, you most likely will begin to see weeds. So the best solution is to understand weeds, how they grow, how they multiply and how to combat that.

I'll be including links to a few Fact Sheets for you to read to gain a greater understanding of what I write. 

First of all, you need to understand the cultural habits of weeds.  

Perennial weeds are ones that have a root system that does not die in the winter. It persists, gets larger, and puts out new growth in the spring.  Unless the root is depleted, it will continue to grow and often spread seeds to create more of itself. The dandelion is one of these types.  Dandelions have a tap root (looks like a carrot). It grows, produces leaves for photosynthesis, puts out a beautiful yellow flower for the bees, then the flower produces seeds which the neighbor children love to blow in the wind and thus plant more dandelions in the neighborhood.

This perennial weed need to have its root depleted. This can be done by persistent digging over time so that it cannot photosynthesize. Also, pulling the flowerhead off after it feeds the bees and closes up. This prevents seeds from blowing around. You can read about a few more perennial weeds here. This is the type of plant that uses an herbicide sprayed on the leaf which transpires to the root and begins to kill the root.

(Please research here the different types of herbicide as one is just for broad leaf plants and the other will kill all plants, including grass.)

The use of herbicides can be useful and less harmful if used carefully and according to the label. By law, the label is the law, and so careful reading is critical. As well, 5% vinegar can be just as harmful as a chemical herbicide.

Annual weeds are plants that put down roots, grow leaves followed by flowers which produce and drop seeds, then it dies only to be outlived by its hundred of seedlings it leaves behind. Unless the plant dies before producing flowers, or the flowers are prevented from producing seeds, annual weeds can be very persistent.  Many annual weeds are grassy weeds, meaning that they grow from a dicot and have a strap-like leaf. Here are a few more examples of annual weeds.

When pulled by hand early in the season, the root system does not have a long time to grab ahold in the soil. This is best done after it rains. A daily "weed walk" can work wonders! 

Because these annual plant seeds rest in the soil until conditions are right for germination, such as soil temperatures and moisture, there is a product called a pre-emergent that controls annual weeds. It's a granular product that is sprinkled over the surface and is watered in, if I remember correctly. It creates a barrier in the soil that causes the seedling that emerges from the seed to die just as it germinates. It will also kill seeds that you WANT to grow such as grass seed or flowers, so application should be done carefully.  

There is an organic pre-emergent made from corn gluten meal that you can read about here.

OK, so now back to landscape fabric. At Extension, our premise is that a deep layer of mulch is better than landscape fabric. It's common to see landscape fabric that has been covered by a small layer of wood mulch for aesthetics, only to find that the wind or a heavy rain will wash or blow the mulch away.  The right kind of wood mulch, one that is shredded, will stay in place better and prevent weed seeds from reaching the soil. A depth of 3"-4" is a good place to start. Additional mulch can be added in future years to revitalize the area.

Small rock mulch can also be used, especially in play areas or walkways. This also should be at a depth of 3"-4".  That being said, weed seeds are more likely to find their way to the soil. The warm environment may encourage germination (unless you use a pre-emergent) but they can be easy to pull.

As an example, I have an 18" barrier between my lawn and a perennial garden on a berm. I wanted to prevent the grass from growing into the berm. So I did use landscape fabric around and at a distance of 18" from the berm.  It does prevent the grass from growing into the berm, however my husband has to pull the grass out of the fabric several times a year to keep it neat and tidy.

Since you are planning to install a patio and planting areas, I would recommend that you plan for a 4" depth of mulch.  An irrigation drip system can be installed before the mulch is applied in the areas where you plant plants. Even xeric and native plants need water to get established, which could be a year or longer if you plant shrubs and trees. So unless you plan to water by hand, consider a drip system that you can learn to control for needed output of water.

For the area that is sloped: have you considered  terracing of some kind? Slopes are tricky for mulch. You could also consider a hardy ground cover. Here is a Fact Sheet from Colorado State University listing groud covers. Even though it does mention the use of landscape fabric with mulch, this would not be good on a slope. Also, if you were to choose a groudcover that you want to spread, such as mother-of-thyme, you want that to spread by rooting along the way.  The faster the spread, the more it might invade other areas. Before choosing a ground cover, I would recommend that you do research, but it could be very effective on a slope.

I think I'll stop now and let you digest what I've written. Then you can reply if you have more questions. if you would like to send photos, that might assist with a greater understanding of what you are facing.

Thank you for allowing CSU Extension to play a part in your horticultural endeavors.

Sincerely,

Dear Patrick,
You would not put landscape fabric under a xeric lawn as it would need to be planted by seed.

Try starting by reading this PlantTalk article then maybe follow some of the links at the end.

Many people are wanting to replace their Bluegrass to save water, but some alternative lawns may not be exactly what you are thinking of.

I’ve reduce my lawn, front and back, by ⅔ by installing drip irrigation gardens or a mulched area where the grandchildren do not play. I kept the remaining ¼ since the children play there. The new term is “functional turf areas”. Pets and children like a nice soft area to play. I planned the redesign according the the turn zone and so I did not have to move any irrigation.  In the mulched area, I capped one head and redirected two head away from the mulch an on to the bluegrass.

 I can try to help you find example images of the right approach to alternatives if you desire.

Sincerely,

Joan

PS Regarding the weed info, regardless of your approach to a new landscape, you will have weeds. So understanding how to approach the prevention and control, you will have a lot less to manage.