Building A Raised Bed Garden (page 3)

Building A Raised Bed Garden (page 3)

Building A Raised Bed Garden (Continued)
By Marge Talt (mtalt(at)

Copyright by Marge Talt. All Rights Reserved.


This garden needed to slope from the steps to a drain at the opposite end so that hard rains would run off and not flood it. A slope of approximately one quarter inch in every foot was needed to make sure water would flow where I wanted it to go. The amount of cut had to allow for the final thickness of the flagstone plus the stonedust underlayment.

Considerable time was spent futzing with a string level and stakes and doing copious mathematical calculations on the backs of envelopes...not my forté. Eventually, I got it about as accurate as I was able to and began the grading.

I've done a good deal of grading, over the years, and the one indispensable tool for this work is my old "come-along". It may have another name, but that's what I learned to call it from the concrete installers who use it to spread concrete. You won't find this tool at the garden center. You need to find a contractor's supply house. They are not expensive and pay for themselves many times over. Mine's been through the wars, as you can see. If you're planning any grading, I highly recommend getting one of these. They are also useful for smoothing out planting beds, leveling gravel - just about any job that requires making an even surface.

The soil in the beds was left at its original level since there wasn't a reason to remove it - lousy soil can be improved. Grading started at the high end, at the foot of the steps. About half way down the length of the garden I realized that my first attempt at masonry with mortar was in trouble.

At the upper left of the photo of the graded area (see previous page), you can see this pathetic item, a catch basin with a fitted cast iron drain. It was meant to be the low point of this garden. As you can see, my initial calculations were a bit off. This had been built several years ago, when the drain tile went in, by excavating a hole and building the brick catch basin in the hole. In a hole no more, it had to have the two top layers of brick removed and the grate had to be reset so that it would be level with the paving.

Setting Stone

Once grading was complete, setting the bed edging revealed another little miscalculation. I'd planned on using nominal two inch thick by twelve inch wide (5.08 x 30.48 cm) flagstones on edge, burying half their "height" for stability. This would make a six inch (15.24 cm) high bed...I thought. But, I soon discovered that if you start out with a six inch high edge at the high end, it's going to be much higher at the low end, since the grade falls from end to end.

The result was that, from about halfway down the length of the garden, the bed edging is buried less and less until at the end of the center bed, the edging is nearly nine inches (22.8 cm) high. Since the edging needed to be level, there really wasn't an option at this point.

After two years, it's holding, but the end joints have separated at the corners of the center bed a bit, leaking the bed contents, and I know it won't take any internal pressure from digging. If you opt for this kind of edging, don't make the same mistake I did!

I managed to get the stonedust hauled, spread and leveled and the beds framed in; the sand bed and one wall bed filled and planted and about half of the paving done before winter set in. The rest of the walk paving had to wait until the following year.

When you have a plan on paper, laying flagstone paving doesn't require a great deal of creative effort, but it is heavy work. Large flagstones are heavy and unforgiving - you have to think about every move so you don't mash a finger.

The flagstones were delivered on big pallets and set in the parking area about sixty feet (18 m) from the work area. The smaller ones could be moved via cart, but the larger ones had to be worked out of the stack and "walked" to their final resting place since I couldn't carry them and they were too large for the cart.

Trial and error disclosed that it is possible to "walk" them on edge by swinging them, using the corners as fulcrums - slow, but it saves the back. Inevitably, when you are laying them in place, you have to lift each stone at least three or four times to get it set properly. No matter how carefully you level the stonedust, there's either too much or too little stonedust under the stone for it to level.

A lever, of some kind, is a necessity for heavy stones. Even very heavy stones can be levered up enough to get a bit of board under them and then worked up over previously laid stone.

When you get a large stone up onto the previously laid stones, always position it so there is a gap under one edge that you can use as a gripping point. To re-lay a heavy stone without disturbing your carefully leveled base, lever it up into a vertical position and walk it across the previously laid stones to the very edge of the spot it is to occupy. Line it up straight and ease it down, letting it drop the last few inches. If it falls too close to the previously laid stone, use a crowbar to ease it out. When the stone seems about right, lay a board on it and, using a heavy hammer, tap it into place. Then, stand on it and rock opposite corners. If they move, you have more work to do; if they stay firm, your stone is just right.

You can level stones "by eye" but using a spirit level is best. When working on a slope, you can only use a level across the slope. You need to keep a string on stakes, marking the fall, to get the proper height as you go down the slope.

Of course, where the stones from the left path met the stones from the right path, there was a certain amount of adjusting that had to take place...including lifting and resetting about six feet of one path which proved to be too high. But, it was finally down and firm.

Once laid, the cracks have to be filled with sand. For this, fine mason's sand is best. Dump a shovel full and sweep it into the cracks. Then, using a fine spray, hose it down to settle it in and repeat the process until the cracks remain full after hosing down.


Strictly speaking, only the wall side beds are "shade" beds, although none of this garden receives full sun all day. The sand bed in the center gets about four or five hours of sun, while the wall side beds only receive about two and a half hours of early sun. Only one of these beds is complete. The other has plants in it, but they put themselves there and will be removed in the near future so I can fill the bed and put in the rightful inhabitants.

This bed was filled with spent potting soil that I'd been dumping in the spot for some time. It grew great weeds and the plants in the bed seem to love it. You can infill raised beds with various mixes. If you want to build one over grass, you can also cover the turf with several layers of newspaper and add soil. Plant roots will penetrate the newspaper, which will rot along with the grass under it.

Think twice about using geotech fabric or weed blocking fabric. It sounds nice, but I've dug many large clumps of plants whose root systems incorporate permanent sections of weedblocking fabric. Plant roots will grow right through it.

Planting, is, of course, the fun part of building any new garden. I'd been stockpiling plants for a while - and, of course, a few simply had to be purchased especially for this bed. The result was rather too many plants for the space, but I put them in anyway.

I'm rather fond of this bed, although it's planted too closely and a few plants have to be relocated. I've already moved the tiny blue Hosta 'Blue Cadet' who was getting swamped, as well as Tricyrtis 'White Flame' who objected to the direct sun last summer. One of the Heuchera is also buried too deeply by the Euphorbia and needs a new home.

The primary occupants are three assorted Euphorbia and four different purple leaf Heuchera. I'm quite taken with the combination of foliage and flower colors these provide. Cheek by jowl with them are:

Geranium sanguineum and G. s. 'Lancastrense' whose starry foliage makes a good contrast with the larger Heuchera leaves.

Geranium 'Johnson's Blue' (not as happy as I'd like - I think it resents the crowding),

Bergenia cordifolia (holding, but not blooming - at least not dying),

Carex morrowii 'Silk Tassel' - a rather nice, fine leafed sedge,

Carex buchananii (the rust colored hair-like foliage at the top of the photo),

Ceratostigma griffithii (whom I hope I haven't killed by too severe pruning),

Indigofera kirilowii who is finally coming into its own and blooming nicely. The foliage on this plant resembles a black locust a bit, an interesting contrast with other occupants of the bed,

Several fall blooming Crocus laevigatus 'Fontenayi',

Some Colchicum,

A Digitalis and a Campanula snagged at a plant exchange whose labels washed clean quickly and whom I do not actually have ID'd...

There's also a Cotoneaster horizontalis cutting I'd made from the garden, a Louisiana iris given me by a friend and one Tellima grandiflora grown from seed.

The effect is quite lush, but I know more shifting needs to take place to keep things on a healthy level. I lost Agapanthus 'Blue Baby', supposedly hardy, who I think succumbed to being flopped on all last summer.

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