Key Questions to Ask When Ordering Tunnell Lliner

When it comes to row covers for your garden, should you go with fabric or plastic? That’s one of the most common questions I get about growing in winter. Which is better?

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In my experience (gardening in a zone 5 microclimate in Central Oregon), there’s no single best row cover if you’re using a low tunnel. It depends on what is being grown and how active you want to be in managing your garden. I’ve experimented with various combinations of row covers over the years—fabric only, plastic only, plastic over fabric—and I’ve found that you can have a productive winter vegetable garden with either setup.

But, certain situations may call for one or the other, as an improperly-selected row cover can doom your garden to failure. How can you decide what to go with? Here are seven questions to ask yourself this season.

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1. Can you get in the garden every day?

This might be the most important thing to consider when choosing the right row cover: how hands-off you want to be. Fabric row covers are permeable to air and thus self-venting. They can stay in place from late fall to early spring as long as you don’t get a freak heat spell.

On the other hand, low tunnels covered with clear plastic sheeting have to be continuously monitored and vented on sunny days. The interior temperatures can easily reach 80°F or more in winter if the daytime high outside creeps up to 40°F.

And warmer doesn’t necessarily mean better conditions for your cool-season crops. Warmer temperatures trigger plants to lose the cellular adaptations and sugars they’ve produced to withstand freezing conditions. (Remember that low tunnels don’t prevent freezes—they just help plants survive winter.)

So how warm is too warm? Generally, if using plastic, you should vent your tunnel if the temperature inside the tunnel starts approaching 60°F. I recommend buying an inexpensive remote temperature sensor (no Internet connection needed) to monitor temps and humidity in winter. This is the one I use in several of my low tunnels.

2. What is your hardiness zone?

Many people assume that clear plastic or glass are the only options for winter gardening, but fabric row covers can work just as well in most of the United States. If your winter lows rarely dip below 0°F, then fabric is a great choice if you can’t or don’t want to use clear plastic.

I use medium-weight frost cloth on most of my raised beds and can grow a variety of cold-hardy crops all winter long, including kale, collards, cabbage, mache, miner’s lettuce, sorrel, spinach, baby Asian greens, baby fava beans, winter peas, chard, and beet greens. I’ve even grown lettuce in the depth of winter by doubling up on the fabric if the forecast calls for exceptionally frigid weather. Most of my cold-hardy culinary herbs also live under fabric covers in winter

3. What are you hoping to grow?

I reserve my plastic-covered low tunnel for vegetables that are less tolerant of hard freezes. For example, baby Asian greens (like tatsoi and komatsuna) can easily survive freezes under fabric row cover, but their mature versions tend to turn limp and mushy. The same is true of other mature vegetables like lettuce, chard, and fava beans.

So if you want to have salads all winter long but cannot use plastic, try to time your sowings so that your plants are in the baby leaf stage by the first frost and can survive under fabric the rest of the season. (Baby Asian greens are very mild and tender, making them the perfect winter salad green.)

4. Are you winter gardening, overwintering, or winter sowing?

Much of what I’ve covered here so far pertains to growing and harvesting vegetables in winter, but what if you simply want to get a head start in spring?

Overwintering varieties of kale, cabbage, purple sprouting broccoli, Brussels sprouts, cauliflower, leeks, and other vegetables can be planted in mid to late summer so they grow all winter under a fabric cover and start to produce in early spring.

Or, you can try winter sowing by direct-seeding spinach, arugula, mustard, beets, carrots, fava beans, or parsley under the protection of a plastic cover. The seedlings will grow very slowly all winter, then take off once longer days and warmer temperatures arrive (putting you months ahead of your neighbors).

5. How much snow does your garden get?

Heavy snow should be removed from both fabric and plastic tunnels, otherwise the weight can cause your tunnels to collapse. A broom or plastic leaf rake (like this one) makes easy work of snow removal, though snow slides off plastic more readily so it takes less time to unbury your garden. (Quite by accident, I’ve also found that a sturdy child-sized rake like this one works well for brushing off snow.)

However, plastic-covered tunnels may need to be vented as soon as a snowstorm passes, which can be challenging if the edges are covered with a foot of snow.

6. Can you water your garden in winter?

Plants still need water in winter, even when they’re dormant. Fabric covers have an advantage over plastic because they’re permeable—so your plants still get soaked in winter rains. In turn, this further raises the humidity inside your low tunnel, providing more protection against winter desiccation.

7. Do you have to shade your garden in summer?

I live in the high desert, which means I often have to cover my garden beds in the middle of summer to shade my plants from searing heat. My low tunnel frames are permanent so I always have a structure in place to protect my plants year-round, whether from cold, heat, or hail.

One benefit of using fabric over plastic row covers is that the fabric can double as shade cloth. I attach mine with clamps, and simply position the fabric on my low tunnel as needed to provide a canopy for my plants. This is super helpful if all you need is a little midday shade; the fabric can be clipped in such a way that it only covers the top of the tunnel (instead of going all the way down the sides).

Where to buy row covers

This is what I’ve used or currently use in my winter garden. To affix the covers to my low tunnels, I like a combination of snap clamps (to really hold down the top) and large spring clamps (for ease of moving the cover and clipping to the edge of my raised bed).

Fabric

The industry standard for fabric row covers is Agribon, though many other brands are available. They’re typically labeled by weight, which affects not only the degree of frost protection, but also how much light reaches your plants.

Because the reduced day length is already a limiting factor in winter, I recommend going no heavier than a medium-weight fabric like Agribon AG-30, which lets in 70 percent of available sunlight and is rated down to 26°F. In a pinch, you can always double up on the fabric if temps drop precipitously low overnight.

If your winters rarely dip below 25°F, then Agribon AG-19 is a better choice since it lets in 85 percent of available sunlight while still offering protection down to 28°F.

Fabric covers do build up heat on sunny days, so it’s important to remove them if your daytime high will exceed 70°F.

Plastic

Clear plastic sheeting is available at most hardware and home improvement stores and yes, you can save money by using construction-grade plastic. But if you’re in a harsher climate or want your plastic to last several winters, UV-treated greenhouse plastic is a better way to go. They’re usually sold in rolls in various lengths, and I recommend getting a 6 mil polyethylene film for durability and ease of handling.

Plastic covers should be vented in winter if the daytime high exceeds 40°F (or the temperature inside the tunnel starts to approach 60°F).

Fleece or poly tunnels

If you have a small garden bed, another option I really like is Easy Tunnels, which are prefabricated fleece or poly tunnels that you fold out (kind of like an accordion) and put over your plants. I used these when I first experimented with winter gardening and that was how I got hooked on year-round growing without a greenhouse!

These compact tunnels already have fabric or plastic covers attached to pre-bent metal frames, so you don’t have to fuss with rolls, clamps, or clips. The only thing I’d recommend adding is a way to secure the tunnel, since it’s so lightweight that it’s prone to blowing away in a big storm. (I zigzagged a thin nylon rope over my Easy Tunnel and anchored it into the soil with landscape pins.)

Got yet another one for the forums. Earlier today, I was working with Hydrocal for the first time in quite a while. I was trying to build a tunnel liner using the Woodland Scenics Tunnel Liner mold. In the process I ended up with a bunch of problems. First, when I tried to put the Hydrocal in the mold, it ran all over the place creating quite the mess. (Most of it was on an unfinished plywood floor, so that wasn’t a problem.) In that process, I was unable to get the back (top surface) of the mold completely level. After I managed to get it reasonably level, I let it sit for the 40 minute cure time. When I tried to clean the excess off, I found that even after letting the casting cure even more, that the material was not anywhere near what I would have expected for hardness. As a result, I ended up throwing the entire casting onto the trash pile.

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My questions are these: Did I do something wrong with the mixing that caused the Hydrocal not to work? Should I have waited longer before putting everything in the mold? Was I not patient enough before I tried to remove the casting? Is there anything else that I need to know about the liners?

As usual, any assistance the forums can provide will be most welcomed.

I would say it was too thin. I’ve used that process a lot starting off using Plaster of Paris to make tunnel walls and that worked good but Hydrocal works better. That being said if you mix either too thin it is super runny. I mix my batches thick almost like a molding mud that you can work with your hands. Hydrocal sets up quickly when mixed thick so you can’t dally.

Edit:

I use touchy-feely method for demolding my castings. Both Hydrocal and Plaster of Paris heats up as it cures when it starts cooling down it’s ready to remove.

If you have a lot of tunnel sections to make be very careful with the WS plastic mold as it will crack easily. Work the mold off starting at the long end.

I’ve really never followed the manufacturers directions, as a kid in the 40s my Mother made Plaster of Paris figurines and I was the pre teen “mixer”. We would spend hours filling molds with me mixing so it’s a natural thing for me.

I don’t use a ratio, I add water to the powder until it becomes thin enough to poor, like an old fashion thick milkshake. One important thing is do not become a tight wad and try to salvage leftover plaster or Hydrocal, once it’s mixed and it has started to setup disturbing the ratio by adding either water or powder screws it up!!! If you need more toss the old and do a restart.

As Mike said for added strength imbed some coarse fabric to the outside of the casting. I’ve been using a 2” wide medical wrap from the local pharmacy, the stuff they use making casts. You can use a spray bottle of water to wet the plaster and use the gauze strip as joiner tape. Mix a soupy batch in a bowl and dip the material in it and apply to the wetted plaster casting like making a broken bone cast.

Was the casting crumbly after it hardened? How old is your Hydrocal, and how have you had it stored?

I got down near the bottom of a big container of Hydrocal one time and had that problem. I think the Hydrocal had absorbed water in its years in the jar, and once that happened it just wasn’t going to work anymore. New Hydrocal, no problem.

I sometimes make curved castings by bending a flat casting around a form after the Hydrocal has set up for about 8-10 minutes. I use clear plastic wrap over the back face of the casting. In your case, you might try pouring the Hydrocal and gently rocking the mold back and forth while it sets up.

It’s a bit off-topic, but this is how I did the interior walls in my subway system:

I bought a large sheet of styrene and cut it into strips. Then, I mixed a thin slurry of Hydrocal and applied it with a paint roller. This is basically how textured ceilings are done. I let it set and sprayed it first with gray primer and then with just a mist of black. At that point, the styrene strips held the Hydrocal but they were still flexible enough to bend them and attach them to the foam walls of the tunnels.

Sounds like maybe your Hyrdocal is old, so may not be a formula issue. However, if I was going to modify the formula for this specific app, I’d go with either 1.5 plaster to .5 water OR 1.25 plaster to .4 water. Basically bump it 10% to 20% toward a drier mixture.

One way to do this is to simply measure the standard amounts, then only pour part of the water in, adding it little by little until you get just enough to get it wet or a little more. It won’t be as strong as it could be, but you don’t need a lot of strength here, just get it to stay in the mold until it dries.

Bob,

Good idea! Gotta love how Sculptamold is so versatile. The advantage it has over the WS molds is that it’s very customizable, especially with curved tunnels…

But you could actually use the WS mold and fill it with Sculptamold, too. It’s going to be much easier to fill and cast with the mold and it holds detail darn near as well as Hydrocal. Plus it won’t break anywhere near so easily and will be lighter than a version cast with plaster of any kind.

That is an interesting idea. I was eventually going to have to get some Sculptamold for my hills anyway, so that might be a good way to kill two birds with one stone as it were. (As I have a lot of Hydrocal portals and retaining walls on my hills anyway, keeping stuff light is a very good idea. And those hills aren’t exactly small either. One of them is roughly 5 feet tall by 2-2.5 feet wide and the other is 2 x 2-2.5 feet. Built from beadboard stryofoam.)

Am I correct in presuming that one would use a putty knife or something similar to put the Sculptamold into the liner mold? As I remember Sculptamold is fairly thick when it is mixed. (It has been awhile since I used that item as well.)

One of the great things about Sculptamold is that you can vary the moisture content accordling to need. It’s much less sensitive to that than plaster, where you can’t get too far off from the specfification or things start going wrong.

I’d take a suitable amount and add water and mix until it’s evenly wet and works easily so you can push it into the mold. A yogurt cup or similar size container woulld allow you to mix a batch right in it. A good stiff-bladed putty knife is ideal for mixing and applying it.

I actually have a couple of MIcro-Mark flexible rubber bowls that I used today to make a couple of batches of the Sculptamold. (Something that I had hiding in my old bedroom at the ranch where I grew up. My Mom found them when she was cleaning and, of course, had no idea what they were! But that’s another story entirely.)

With a little bit of practice, the Sculptamold was quite easy to work with. In the process, thought, I have run into a slight problem: I ended up with air bubble remnants in the castings. (The four that I have can be used in hidden areas as the tunnels aren’t daylighted all the way throught.) I presume that I didn’t vibrate the forms enough.

What would be the best idea for solving that problem in the future? The best idea that I can come up with would be one of the cheap 3-legged vibrators that a certain box store carries. If there are any other ideas, please let me know.

That sounds about right. You don’t want it soupy or even a slurry. But you want to work up the flavor or binder stuff so it’s nice and wet to fill those bubble spaces instead of air.

I mounted my mold to a piece of wood IIRC. Tapping it could help, I was just thinking that the secret is in the sauce on this more than technique. Don’t be afraid to add more water right at the beginning if not mixing wet enough for you. Same with throwing in some more Sculptamold if too wet. Unlike with plaster, this won’t hurt if you’re still mixing and haven’t stopped stirring yet, so to speak.

I tried the idea of my 2:3 mix on Saturday while waiting for family plans to come together. Unfortunately, for some reason that mix ended up way too wet. The castings ended up too thin and even after 24 hours (approx.) the castings hadn’t cured. They broke apart when I tried to unmold them. I also discovered that even with that mix the castings ended up having air buble remnants. I ended up using the pieces which were still flexible (Play-Dough consistency) and plugged some scenery holes with it.

I then tried a 1:1.25 mix. While that mix still had a few bubble remnants, it cured fairly quickly and I was able to unmold them easily. I think I will run with that mix as it molds nicely and it also is nice to work with when I’m covering hills.

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