How to Construct a Raised Bed with Low Tunnel

[whoose]

How to Construct a Raised Bed with Low Tunnel

This post is intended to be an experiential based discussion of how to make a raised bed. There are many consideration that I will try to cover and some controversies. I will have Tomatoville post for reference from many discussion that already have been had controversial topics.

My credentials: Psychology Professor by trade (retired), I have been a home owner level carpenter all my life, I built a log house, two garages and a greenhouse. I have done maintenance on these building for the last 40 years. I have tools, not that modern, but sufficient for the task. Last year I built seven raised beds, five with low tunnels. I plan one more raised bed for this Spring.
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Please feel free to add to the discussion, we all are here to learn from each other.

Why build a raised bed?

Many of us are happy with our container gardens or regular garden spaces. Some of us want to expand to the next level of the raised bed.

Some of the advantages of raised bed are:

• Maximizing the amount of soil for growing plants.
• Allowing for easy applications of compost and fertilizer.
• Easier control of weeds.
• The ability build soil is enhanced.
• Raised beds just look nice.

Where to build a raised bed?

Ideally a south facing exposure on level ground is the most desirable. Many of us are not lucky enough to have this ideal.

Try to avoid these situation.

• Trees, brush, tall grass, large roots.
• Rock outcrops that are not level.
• Long distances for your water source.
• Shade.

What to use to build a raised bed?

Almost anything you can stack, form or pile will work:

• Clay Bricks.
• Concrete walls.
• Cinder blocks.
• Retaining wall blocks.
• Hay bales.
• The buckets from your container garden.
• Wood.

Most of use think of wood as the primary material used for construction of raised beds. There are many types of wood available depending on your location and how much money you are willing to spend.

Types of wood include:

• Redwood.
• Western Red Cedar.
• Eastern Cedar.
• Cyprus.
• Pine.
• Fir.
• Hardwoods.

Just about anything that is natural wood will work.

• No plywood please.
• No railroad ties either.

The amount of time it takes wood to rot in soil depends on the wood type. The most expensive woods (Redwood, and Cedars) last longer than Pine and Fir. So depending on how long you expect the raised bed to last and your budget you can pick the type of wood.

There has been a lot of discussion on using treated wood on this forum.

Pressure treated wood is treated with an arsenic-like compound in most cases.

The some questions to consider:

• How much leeches into the ground?
• How much leeches into your plants?
• How much longer does treated wood last than regular lumber?
• How long does it take for the chemical to break down in the environment?

For question that you will have to consider, see the following:

Pressure treated lumber and raised beds http://www.tomatoville.com/showthread.php?t=43231&highlight=treated+wood

Treated lumber?http://www.tomatoville.com/showthread.php?t=4771&highlight=treated+wood

Paint for raised beds?
http://www.tomatoville.com/showthread.php?t=38776&highlight=treated+wood

My view is why take the chance???

For me it is hard to say Organic and treated lumber in the same sentence. So if you are organic probably do not used treated wood. I use 2X Western Red Cedar, very expensive but why take a risk? The cedar beds will out last me for sure. I have two grandkids and prefer not to take any more chances than necessary with their health. If you sell your produce you must consider the implications of using treat wood.


So Lets Build Some Raised beds

You now have decided on the site and type of material. I will discuss using dimensional lumber for raised beds.

Buy your lengths of lumber carefully, this stuff can be really expensive. Use even 2 foot dimensions for the long sides and try to have to make only one cut for the short sides. For example 8'x4' is a no waste bed with only one cut from 3, 8 foot boards. Many of us do not have power carpenter tools like precision saws. A good way to solve this problems is to have the big box or local lumber yard make the cuts for you, only a dollar of two, and very precise cuts, which you will need.

How to join the sides, front and back of the bed?

I use 4X4 posts in each corner and sink large bolts through the 2X into the 4X4, this will not fail for a very long time. The 4X4 method also allows for easy addition of the next course of boards. I leave the 4X4 about 1 inch below the finished soil for a nice look. You can use metal corner braces, get as big as you can, they will also last a long time. Use only treated non-rusting screws, nails loosen and work their way out. I put a 2X4 as a brace between the front and back in the middle to keep the boards from trying to bow out from the weight of the soil. This brace is also a good place to sit.
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How high should my bed be?

I start with 2X12 boards for the bottom course and then can add 12, 10, 8, or 6 inch boards for the next course. I find 20 inches is about right for me, try out different heights and find the one you like. Remember to leave your corner 4X4 the correct height for the new course of lumber. The bed makes a great seat, the older you get the more you appreciate a good resting area.
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Raised bed height
http://www.tomatoville.com/showthread.php?t=43033&highlight=treated+wood

Building on a sloping area?

You will need to drive large 2X4 stakes in the corners and middle of the bed to keep it from moving down hill. I also place stakes on the uphill side to help slow the movement. Worst case is the bed migrates down hill until it breaks the wood or pulls the screws.

Where to Build the raised beds?

I like to comfort of my garage for the construction of the raised beds. I then put the bed in my truck and take it to the site. I almost always have projects during what we call the "mud season" or Spring here in the West, so nice dry, warm work place is nice. You can build in place but use saw horses to elevate you work.
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Screening the bottom?

I use hardware cloth, small metal mesh, on the bottom of my beds. I have Voles, Moles, Gophers, and other burying rodents that I do not want in my beds. The hardware cloth stops them dead. If you are a double digger leave the screen out. See, below.

Birds? Mice? Rats? Squirrels?
http://www.tomatoville.com/showthread.php?t=42604&highlight=mice

Landscape fabric

Also consider using landscape fabric in the bottom of the beds to help control any weeds trying to grow from the bottom of the raised bed.

The soil?

First decision, organic or not. Your call, see.

Organic/growing compendium and resource listing
http://www.tomatoville.com/showthread.php?t=4636

How to buy soil?

Bags are easy but expensive. Landscape contractors are cheaper and have good access to very good soil. They will also will deliver large amounts to you site relatively cheaply. Try to make your own compost going forward. See.

Compost bin and building compost question
http://www.tomatoville.com/showthread.php?t=36787&highlight=treated+wood

Chicken poo and sawdust
http://www.tomatoville.com/showthread.php?t=40453&highlight=treated+wood

Additives

Another consideration with commercial soil is the uses of bio solids, sewer bi-products (sludge) in soil mixes. The manufacturer must list bio solids in the list of ingredients. Very different views by different people, but it is you choice. See:

Sewage (bio solids) in your compost?
http://www.tomatoville.com/showthread.php?t=42694&highlight=whoose


Low Tunnel

While you are at it add some low tunnels to your raised beds. Very easy, quick and relatively inexpensive. The advantages of low tunnels are about 1 month early planting in the Spring and 1 month longer before killer frost in the Fall. That is a big deal at 6000 feet in the Northern Rockies.

You also get what I consider to be a very important edge, higher soil and air temperatures. These might be the missing ingredients in a successful garden, especially at higher altitudes with short seasons. Where I live the temperature rarely gets over 80f and 50f at night, so hot soil and air really area must.
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Lets build a low tunnel

I use schedule 40 white 1/2" PVC plastic pipe for the hoops in a low tunnel. For the end supports of the hoops I use 1' schedule 40 white PVC plastic pipe, attached with galvanized brackets. Very easy to install and last for a long time. Be sure to try and bend the pipe for the hoops after it has been in the sun for a while, or use a heat gun. Schedule 40 is tough stuff but you can break cold pipe. Stay away from the cheaper thin wall pipe, it is bound to fail. I disassemble my hoops for the winter and store out of the weather.
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Covering for a low tunnel

I use 6 mil clear poly plastic. Lumber yards sell very large roles of the stuff, it is not cheap, but worth it. Do not try to save money with 2 or 4 mil it will fail far too soon. The 6 mil will last one season and then it is off to recycling. Some specialty green house stores have higher quality plastic but I find the cost too high.

You live in a HOT climate and do not need the heat provided by a low tunnel or the extended season. But you can still use the low tunnel, you will want to stop lost of uninvited guests. See:

Birds? Mice? Rats? Squirrels?
http://www.tomatoville.com/showthread.php?t=42604&highlight=mice

You can use netting/screening to stop most mammals, insects, birds for destroying your plants.

Too hot in the summer is a problem many of us would like to have but if you do have too high temperatures you need to mitigate the problem. You can put shade cloth over the low tunnel and provide shade and lower temperature. See:

Thoughts on shade cloth
http://www.tomatoville.com/showthread.php?t=43248&highlight=whoose


Ending Thoughts

So let me know your experiences and how to improve my basic raised beds and low tunnels.

[imp]

Very good post and a lot to think over. I haven't used much in the way of raised beds, so will have a great deal to think about before further comment.

[Banadoura]

Great post W!

The low tunnel means you need to uncover and recover the raised bed on a daily basis in the 2 extra months you gain correct?

What is your cost estimate for a low tunnel per raised bed?(the pvc pipes + 6mil plastic)

Thanks for sharing,

[whoose]

You do not want to open and close early or late. Not that hot that it makes it necessary. Summer just take off half the sunny side and leave the back on. All the part for a low tunnel less that $25 USD

[MissS]

Thank you so much for creating this tutorial. It seems very well thought out and you put in some nice effort to answer many questions. I hope it comes in handy after I get my new house.

[rhines81]

Originally Posted by whoose

How to Construct a Raised Bed with Low Tunnel

Pressure treated wood is treated with an arsenic-like compound in most cases.

The some questions to consider:

• How much leeches into the ground?
• How much leeches into your plants?
• How much longer does treated wood last than regular lumber?
• How long does it take for the chemical to break down in the environment?

For question that you will have to consider, see the following:

Pressure treated lumber and raised beds http://www.tomatoville.com/showthrea...t=treated+wood

Treated lumber?http://www.tomatoville.com/showthrea...t=treated+wood

Great subject. Nice job.

There are many people recycling materials to use as raised beds. Pressure treated lumber made after 2004 no longer contains arsenic as a preservative, so unless someone is recycling old, there should be that much of a concern ... besides, I had read a study from back in the day - and the average person got more arsenic in their system from eating Rice than from anything else ... I didn't save the sources from the references, but I am sure anyone concerned can re-Google the info.
Newer treated lumber uses more copper type compounds, which (who knows) seem to be safer.

People can save a lot of money by drilling their own holes and cutting their own wood to size. Building a few beds from scratch instead of buying "kits" even pays for the cost of the tools that you can use for 'whatever; around your home for other projects.

[rockman]

Nice setup whoose! I Like my raised beds for all the reasons you mentioned. Hudson WY has a setup like yours on a larger scale that you would really appreciate. If one was thinking raised beds and tunnels after looking at yours and HudsonWY's they would be hooked. Hudson WY's pictures are in General Discussion page 2 under adashofpepper's topic 1st year growing carrots page 5 and 6.

[PhilaGardener]

Great beds!

I'm looking for a cheap source of recycled plastic lumber (having gone through several rounds of wood beds). Plastic pallets, maybe? They seem more precious than wood ones and I haven't found a good source yet. Has anyone figured that out?

[jmsieglaff]

One heck of a nice writeup, thanks for posting it. Not sure I have anything to add except what I did for my raised beds.

When we bought our house there was a timber 8x8 garden with decent soil in it. I wanted to expand a little bit. I did want to maintain raised beds without bottoms as the existing soil in the area was pretty good. I wanted something with little maintenance.

So I built 2 4x11 foot beds using split-faced construction block. The blocks are 8" long by 8" height by 4" deep. I used a grinding blade on my circular saw to score blocks where they needed to be cut and a hammer and chisel to split them. I built the beds in 2011 and they are as good as the day I put them in. I filled the cinder block holes with compost and grow dwarf marigolds and herbs in them. I add compost to the beds twice a year, once in fall and once in spring and will feed plants when/as necessary.

The long dimension of the beds run east-west, which along that long dimension I have cattle panel trellises, framed with metal electrical conduit. They are slipped over rebar which I drove into the ground, the trellises live outside 365 days year. I grow peas, cucumbers and squash on them.

At some point, like you have I want to play around with low tunnels over a bed for extra early spinach, etc.

They look like this:

[whoose]

Look for decks that are being replaced for plastic wood. The stuff is expensive new but used it is trash. Try redwood or cedar if you can find it.

[creister]

Lowe's carries 8x6x5/8 western red cedar. they are around 4 dollars each. I was going to use them to build a 4 x 12 bed.

[whoose]

God price for Cedar, pick the pile for the best without knots. Stake the side well and you are in business.

[b54red]

I have been using raised beds for over 30 years made with the old arsenic treated lumber. From the density of earthworms and their propensity to really get thick right up next to the wood I would say the leaching is not much of a problem. Despite being in the center of termite country the wood is still solid but all of my treated 2X4s that were used for support have had to be replaced several times. The wood I used is true 2X8. I wish it was a bit deeper but not more than 12 inches.

My beds are made on a fairly steeply pitched area where I tried gardening without raised beds for a few years but a couple of heavy rains washed most of my garden into my neighbors yard a few times and that made the decision easy to make. Another advantage is raised beds really cut down on the wait after a heavy rain before the bed can be worked whereas in a flat garden it can takes weeks for the ground to be usable after a really heavy rain. With raised beds the longest I usually have to wait is about 3 days.

I made a couple of mistakes that have given me problems for all the years since I made the beds. One I didn't leave enough space between the beds. I only left around 2 feet between them and if I had to do it over I would leave at least 3 feet. The other mistake was making the inside width of all of my beds a full 4 feet. That seems fine when you are a young man but as time went on I have found it more and more difficult to work the centers without stepping into the beds. I think if you are of average or greater height and don't have really short arms somewhere around 40 to 42 inches wide would be ideal for most beds. If you do make your beds out of wood expect some big time warping over the years as the wood absorbs water and dries out again.

Most big box home improvement stores sell pvc conduit that is gray and it works better for the hoops than the white as it is more flexible and more resistant to break down from the sun. Even on the coldest days I have never had a piece break when setting up the hoops. It comes in 10 ft lengths and I just cut off the female end of the pvc conduit and just press it into the beds on each side then use 10 ft wide poly for my cover using staples to seal it to the bed. I use far more staples on the permanent side and use as few as possible on the side that has to be opened in order to pull back the covering. On days when it is still fairly cold and with nights that are too cold if it is sunny I just open the ends and use a couple of large clips to hold the plastic sheeting back so that air can flow through and stop it from getting too hot during the day.

Despite living way down South I use hoops every winter to protect my plants that can be killed or damaged severely by temps in the low 20s which happen enough to need them. I like the way broccoli, cabbage and cauliflower taste better during the winter than any other time and the hoops make it possible for me to enjoy them when they are at their peak. The winter is really the only time lettuce is really good down here and without all the bugs that come with warm weather. All these type plants get much stronger tasting when the hot days of spring arrive but they also get much bigger then. The hoops really give Brussels sprouts a big boost by keeping them growing fast during the colder times which results in them being much bigger during the short spring we have when the sprouts are making. I however do not use them to get an early start on tomatoes and peppers as our season is so long anyway. I have found it just easier to wait another week or two but for people with a shorter season and a much cooler spring the hoops would be wonderful for that purpose. They could also be used to warm up the soil before planting which helps tomatoes a good bit when planting them early.

I highly recommend the small home gardener use raised beds because of the time saved maintaining the garden, the reduction of flooding problems, the ease of improving the soil and the very real improvements in production. The one big draw back for me is certain crops don't lend themselves to raised bed gardening but most of those need much more space for growing than most home gardeners want to devote to them. The other disadvantage is they do require more frequent watering so it is important to build up the organic matter in the beds so they hold more water longer and using a good mulch.

Bill

[rockman]

jmsieglaff, good idea planting herbs and flowers in the block holes. Is that 3' tall Rhubarb in the distance?

[jmsieglaff]

Originally Posted by rockman

jmsieglaff, good idea planting herbs and flowers in the block holes. Is that 3' tall Rhubarb in the distance?

Sure is. It's our neighbors and we have a standing help yourself order,which we do. DW makes a fantastic rhubarb coffee cake. Our neighbors have the better end of the deal though, they get weekly deliveries of tomatoes, peppers, squash and cucumbers.