Zilker Neighborhood Gardens

Commentary by a National Wildlife Steward who helps Zilker neighbors establish native plant gardens

Tag Archives: soil solarization

Soil Solarization … Update on the New Garden

 

In March, I wrote about solarizing a new planting bed in the front of my house. In that post, I described with pictures our process of scalping the lawn, watering the area, and covering it tightly with plastic (black or clear is fine; generally clear is better). I put the plastic down around mid-March and it lasted just fine through June. Occasionally a blade of grass might poke a hole through the plastic (didn’t know grass was that sharp!) but I would just readjust the plastic and put more rocks down on that area to cover the hole.

In June, I finally had time to tackle the bed. The first job was figuring out what I was going to plant. I had measured out the front yard and made a paper layout of the garden bed, to size, so I knew how many inches equaled a foot of space. I read up about native plants, pouring through resources I have, books, and checking against LadyBird Johnson Wildflower Center’s native plant database. I considered the plants that were already planted in the front yard on the other side as I hoped to create some symmetry of color. I also wanted a little bit of height, but not as tall as a tree because this bed sits immediately in front of the front door of the house. I did not want to block the sight-line of the front door from the stree/sidewalk with a tree. The area is in full-sun, so I had to choose plants that could withstand the heat.

I came up with the following plan. The plan includes:

Front Garden Plan

  • Lamb’s Ear
  • Purple coneflower
  • Silver ponyfoot
  • Black-eyed susan
  • Gayfeather
  • Henri Duelburg Sage
  • Jerusalem Sage
  • Mexican Feathergrass
  • Firebush
  • Texas heartleaf hibiscus
  • Tall Rosinweed
  • Grandma’s Rose (yellow)
  • Martha Gonzales Rose (red)
  • Globemallow
  • Yarrow (white)

On my paper version, I take care to estimate out the plant’s mature size in order to give it enough room. Thus, when you plant initially, your planting bed might look a little spare. But don’t worry, plants seem to grow so fast here in Texas that your garden will soon be lush. I was going for a color scheme, from front to back, of white, red/orange, orange, yellow, purple, white, purple. It didn’t quite work out exactly like that but good enough. The yarrow introduces white at the front, then the globemallow (orange), red roses and hibiscus, and firebush have reds. The yellow comes from Grandma’s rose, Tall Rosinweed, black-eyed susans. Purples come from Jerusalem sage and Henri Duelburg sage, gayfeather, and purple coneflower. (Note: Gayfeather was not available at time of planting.)

Once I had my plan, I decided that this time I’d hire some strong people to dig out the dead grass for me. I killed myself the last time and my husband was not too keen on doing it either. What a good decision! It took 2 men about 2 hours to completely dig out the grass and turn the soil a bit.

Here’s what the area looked like when we removed the plastic and after the dead grass had been dug up.

Area underneath the plastic

Dead grass revealed after plastic removed (above)

    Area after dead grass dug up

After dead grass dug out (above)

After amendments

Soil amendments added (above)

After the hired guys dug through and rid the area of most grass, I went through and broke up big pieces of dirt and also checked for grass roots (they are so invasive!). We added a lot of compost, green sand, and corn gluten as I recall. We raked the amendments into the soil, catching more pieces of grass root. My husband installed edging along the grass side of the bed in order to reduce the invasion of grass, which is inevitable.

We had this work done on Saturday. After the bed was prepped, I went out and bought my plants and planned to plant on Sunday after the sprinklers had moistened up the soil.

Planting was super fun! I bought all 4″ pots if I could find them. The plants grow SO fast – there is no need to buy bigger plants unless you are impatient. The roses were a splurge and I did buy larger roses. Here are the pictures of the garden planted in mid-June.

Bed planted

Purple coneflowers and Lamb’s Ear (left, above)

Bed planted, front of bed near sidewalk

Front of bed. Mexican Feathergrass, Lamb’s Ear, Yarrow (left to right, front)

Globemallow (center); roses (right center)

Symmetry at last

Symmetry in the beds at last. Getting closer to my semi-formal garden.

The last task, of course, was to put mulch around all the plants and on the bed to reduce weeds and to retain moisture. Lucky for us, Home Depot had a great sale on mulch. I also designed in a small, dry creekbed. On the other side of the sidewalk (not in picture), a gutter downspout had typically dumped water onto the driveway which flowed to the street. I added a different endpiece and now the downspout dumps water onto the sidewalk that flows into the small creekbed within the planting area. Silver ponyfoot is planted at the right corner of the sidewalk/driveway near the creekbed.

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The plastic soil solarization approach

It’s time for another round of soil solarization. If you recall, last year at about this time, I used the newspaper + mulch method to kill the grass to create a planting bed. Well, that approach was not very successful with our St. Augustine grass. It worked out OK but I had to go through and weed grass out of the beds twice before the fall when I finally planted plants in the beds. It seems most of our St. Augustine died and Bermuda grass volunteered in its place. So, now we are trying to kill Bermuda grass which is a bad, bad invasive.

So this time, we are using plastic instead of the newspaper and mulch approach. Following are pictures of the steps we took. There are varying views on if you use black or clear plastic. In my reading, I finally came to the conclusion to use black plastic in the cooler months (winter, spring) because it will also keep out the light that could help grass grow. In the hottest months, you should use clear plastic because it will allow all the sunlight through and create an inferno under the plastic. Whereas, black will reflect back some of the light and thus, not get as hot during the summer. So, ultimately we chose to use black plastic for the next few months.

Step 1: Draw out your design. First, draw it in your mind, then on paper, and then on the land. I used landscaping spray paint I bought at home depot ($5). That red line you see is paint. I am creating a semi-formal design so you can see the new bed on the right will mirror the bed I created last year on the left side. Using a measuring tape, I created the mirror image bed’s shape. Due to our lot size, sidewalk, and house placement, the right bed will be larger than the left bed. I decided to plant the oak tree in the round middle area in line with the house’s front window so you could see it from inside. Planting it dead center on our grass didn’t seem right (the grass on the far left is our neighbor’s). So you have to make some decisions like that. You don’t have to go out and buy paint – you could just use plain old baking flour and dust it along your shape. You could also use a hose to arrange the shape. Since I was not going to do all the steps on the same day, I didn’t use flour because it would blow away by the time I got to Step 2. The paint is permanent but quickly fades and would be mowed away within a few weeks if you changed your mind.

design your planting bed

Step 2: Scalp the grass. Next, we mowed the grass in this section as low as the mower would go. Then, we used a trimmer to scalp the grass down to the dirt. We tried to get every morsel of grass out of there (which is impossible) but the more, the better. It’s a dusty job – wear a mask if you can! When you are done, there will be a lot of grass shaving to brush up and put in your green waste bucket. If it is Bermuda grass, give it to the city’s green waste rather than your own compost. You don’t want that grass in your compost. We also took rakes and raked all the grass shaving out of the area to be swept up. I don’t recommend using a blower as there’s a lot of dirt now, and you’ll just create a big dust storm. Just use a broom to collect it and put it in green waste.

Scalping the grass

Scalp the grass

 

 

 

 

 

 

 

 

 

Step 3:Water the area deeply. Next, you want the area to be very moist. When you put the plastic on top, the moisture and the heat will allow it to become hotter and the heat penetrate more deeply. We turned on our irrigation sprinklers. After 15 minutes, I stuck a screwdriver down into the soil to discover that it was not wet at all. So we followed up with a local sprinkler to get just this area. Once adequately moist, it’s time to add the plastic.

Water more

Water the area deeply

 

 

 

 

 

 

 

 

 

Step 4: Lay down the plastic. As discussed already, we chose to use black plastic. I bought a role of 3.5 mil black plastic at Home Depot for $10. I thought it would be large enough for our area, but it was not. Luckily, we had some black plastic bags that we cut and duct taped to the rest of the plastic to finish the job. You really need two people to do this, and do not try it on a windy day (especially if you have only 1 person!!!). We cut a trench using our edger along the grass side so there was a slight trench into which could add the plastic. The deeper a trench you can create, the better to prevent whatever is on the other side of the new bed from penetrating into it.

We laid the plastic down and my husband shoveled up rocks we have available and we mounded those along the edge. Make sure the plastic is as flat and tight as possible to the ground. This helps heating as well as prevents wind from damaging the plastic or blowing it away. You should not have any holes in the plastic or the whole point will be sabotaged. Once we had our plastic in place, secured with rocks, I cut any extra plastic from the edges off with a scissors. Just after we were done a large, gale force wind came along, and our plastic passed the test!

Plastic in place

Step 5: Wait. Now we wait for several months for the grass to (hopefully!) die. If it doesn’t die off, we may recover with clear plastic in May when it gets hotter and see how that works. We suspect we will still have to do some digging to rid the area of deep grass roots that may persist. We will also put in metal edging to prevent grass from entering the area after our bed is created.

If you create a bed, know that you will always have to do a little weeding in it. There’s no 100% solution to weeds (a weed is anything you don’t want in your area). Even xeriscaped areas with rock will have weeds. But, I have to admit that I am LOVING my small gardens we’ve put in so far. I can’t imagine how happy I’ll be when the rest of the garden is done.

Soil Solarization – Killing More Grass (without chemicals)

Well, I implemented the newspaper and mulch method to kill grass/weeds on part of my front yard and my back yard, which I described in an earlier post. The backyard worked pretty well requiring only a little weeding here and there – mostly because squirrels buried oak acorns into the ground, and they are popping up.

The front yard has been more of a challenge. As I wrote about earlier, some grass is popping through my newspaper and mulch area in the front yard. I’m a bit disappointed with this. The method has killed the St. Augustine grass that was below it. But what seems to be growing is some bermuda grass, one of 24 most invasive plants by the City of Austin. I have decided to remove the mulch and newspaper, dig up the dead grass, till compost in the soil, then plant, then put mulch back on. This will be a chore, but I am certain I will be much happier with the planting bed. At this point, I’ve only planted trees in the beds, and I’m still having a hard time deciding on my plant choices.

I have a semi-formal plan for my front yard and the garden bed I prepared with newspaper and mulch is only HALF of the plan. So I still have another half of the yard to kill grass on. I have decided to try soil solarization on the other half. One of the speakers in our Habitat Steward training discussed this method, and I know many of you have used it.

The point of soil solarization is to get the sun to heat up the top 6″ or deeper of soil and kill all the weeds (or grass for my purposes). Contrary to what many people think, you should use clear plastic that is 1-6 mil in thickness. Some sources say 1-2 mil is better as it lets more of the sun through. In our climate right now, soil solarization is the perfect way to go since it is so hot and the sun so direct. (In cooler climates, one can use black plastic but I won’t go into that here for Texas. Use clear plastic, especially in a sunny area in the summer.) Might as well take advantage of our heat wave!

BENEFITS

Solarization during the hot summer months can increase soil temperature to levels that kill many disease causing organisms (pathogens), nematodes, and weed seeds and seedlings. It leaves no toxic residues and can be easily used on a small or large scale garden or farm. Soil solarization also speeds up the breakdown of organic material in the soil, often resulting in the added benefit of release of soluble nutrients such as nitrogen (N03, NH4+), calcium (Ca++), magnesium (Mg++), potassium (K+), and fulvic acid, making them more available to plants.

Plants often grow faster and produce both higher and better quality yields when grown in solarized soil. This can be attributed to improved disease and weed control, the increase in soluble nutrients, and relatively greater proportions of helpful soil microorganisms. (http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74145.html)

Before you put the plastic down, the ground should be soaked with water, as wet soil conducts heat better than dry soil. Having the soil moist seems important, and you might to wet it during the process (life up and edge and spray water in) – sources indicate this might reduce the temperature for a time, but overall is important for the solarization to occur.

One of the keys to success is getting the plastic as tight as possible to the ground. So I plan to mow the current grass as low as possible in the area I want to solarize. I will also edge the area deeply so I can secure the plastic tight down the ground. You can also use bricks or rocks etc. to keep the edges down. It will be hotter if there’s less billowy air pockets inside. We do get a fair amount of wind, and you don’t want your plastic to set sail.

Then you wait 5-6 weeks. Have a few cool drinks and know that you’ll get to the gardening when it is cooler outside!

An excellent resource on soil solarization can be found from the University of California. They have further, very detailed downloadable packets of information here.

The Natural Gardener also has a short description of soil solarization. They have slightly different advice on the preferred thickness and length of time to keep the plastic on than the UC source.

I welcome comments regarding this approach – have you done it? How effective was it? Any challenges? Personally, I sure hope this works as the alternative of digging the grass out by hand is not optimal.

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