Saturday, May 8, 2010

Building a raised bed

Building a new raised bed is not difficult, but you will want to plan it out before starting. I am putting in a new asparagus bed to correct my too wet old bed. This blog will review my plans installation. I welcome any comments or suggestions.

Lumber:  I plan to have this raised bed for a while, so I am building it out of hemlock. Hemlock is naturally rot resistant, so I don’t have to worry about ground contact. Hemlock is strong and inexpensive, too. On the other hand, hemlock can warp and will expand and shrink with the seasons. That is not a problem for me. I will reinforce the sides (with some leftover flooring lumber), but a little warping will just give the raised bed character. I purchased 2” x 10” x 4’ dressed hemlock from Maschino Lumber in New Gloucester. You could use rough hemlock to get a more natural appearance, but I prefer fewer splinters. Their price was $4 per board. I used 8 for this so the lumber cost me $32. 

Soil:  I am filling this bed with a combination of finished hot compost, vermicompost, leaf mold, and peat. It is mostly hot compost with a little vermicompost/leaf mold/peat to increase the organic matter content. I made a lasagna style raised bed with these other additions. Because this will eventually become strictly an asparagus bed, I am being very careful about weds (vermicomposting is not hot composted, so I will battle volunteers if I add a lot of it too close to the surface. I will water the plants with vermicompost tea later, so I don’t need to go overboard with the vermicompost now. Compost and leaf mold are free. I used very little peat, but a new bag is $4.

Other:  I used 3” deck screws to hold everything together. Because hemlock warps and shrinks, I chose screws over nails. I already had the screws, but if you were buying them new a medium box costs around $6. I also used hardware cloth (secured with staples). I am using hardware cloth to stop any mice, moles, voles, etc. from tunneling into my raised bed. I’ve suffered from their raids in the past and an ounce of prevention... More on this later.

If you’re going to garden in your raised bed, don’t make it too large. The idea is that you don’t want to walk on the raised bed, so you have to be able to reach the entire area. For me, that mandates a design that is not more than 2 feet from any side. Here a 4’x4’ square that I can walk around is perfect.

I’ve had problems with underground raiders in the past, so I am adding a bit of insurance to deter them to this bed— hardware cloth is stapled to the inside bottom of the frame. ACE sells 1/4" hardware cloth 24” for around $2/foot. I need 16 feet, so $32.

Site Preparation
I removed sod from an area a little larger than my 4’x4’. Then I excavated soil to a depth of approx 16-18”. I want good soil down 2’ deeper than the soil surface, so I have to excavate to this depth. It is hard work, but it will be worth the effort later. Add the excavated soil to your hot compost pile (you can see one of my hot compost material storage piles in the background). I used ground stakes to help me dig straight lines.

When the site is ready, assemble your raised bed. Eight pieces of 2”x10”x4’ lumber is heavy, so I suggest you do this close to where you will be installing. I end screwed the boards (twice each) and braced the centers with a piece of scrap flooring lumber (on the inside so this will be hidden by the soil). When built, place over your hole. As you can see, because the hole is larger, I have to span the corners to position the raised bed frame. I have lots of scrap flooring, and this works perfectly.

Next you staple the hardware cloth to the frame allowing about 10-12” below the bottom. This can be tricky because it is not too flexible and hardware is VERY sharp. Wear leather gloves and a long sleeve shirt.

Now comes the fun part: adding in your good soil. As mentioned, I am making lasagna layers with leaf mold and peat (over sprinkled with vermicompost). My top layer is finished hot compost. Water down the whole thing when you are finished, and poke with hay fork to remove any air pockets.

Back fill the outside edges to secure the frame, and remove the flooring. Tamp down the soil around the edges and you are finished.

I planted with asparagus and beets. I will add more asparagus next spring. I want to have 2 varieties Mary Washington and Jersey) to give me some diversity for pest resistance.  This raised bed cost me a total of $74 and took 3 hours to complete. Although my new asparagus will take several years to establish, I plan to harvest asparagus from this bed for a LONG time. Great recipes for all your home-grown or CSA vegetables can be found here.

Eventually, I will dig out the surround grass and replace with landscape fabric covered with wood chips.



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