Raised Beds over Synthetic Lawn?

I'm new to the forum and new to gardening. The sudden interest has been brought about by recent world events.

Pperhaps you can take pity on me as an extreme novice. This may be an odd question but I am stuck with what items I have because I've been unable to get wood and top soil delivered.

My garden is as it came with the house I'm in. It has a synthetic lawn. It was well layed and has needed limited attention for 5 years. Weeds do grow in it a bit. Under the "grass" is a membrane and then compacted sand and gravel, this is about 6 inches deep and then there's clay. The soil in the garden is either rubble or clay.

I've been able to acquire a limited amount of cast-off top soil and 500 litres of general use compost. We also have a full composter from garden/kitchen waste. Further to this i have some old floorboards and shelving wood (I know these will rot but this is a temporary arrangement with the stuff I have, i expect that they will probably only last a couple of years at most).

The intent is to fashion some raised beds for vegetables in so far as is possible with the bits I have. I would make it 12 inches deep. It won't be huge, 6 ft by 4 ft perhaps.

The question is: Do I install the bed ON the synthetic lawn OR cut a suitable hole for it in the location of the raised bed? I'm not worried about messing up the lawn.

My thoughts are:

A. Take section of lawn up:
1. The gravel underneath may drain too rapidly and also let soil wash away.
2. with no means of fixing the new edges of lawn it may well move and wrinkle.
3. I could dig out some gravel - this may help the over-drainage issue but also undermine the adjacent lawn areas.

B. Build on top of lawn:
1. perhaps not enough drainage
2. No worms - i can solve this because the composter has a lot of worms
3. roots cannot go deeper than the soil i put in. i.e. this is just a big planter

Any thoughts? Social distancing and closure of shops makes the scope more limited.

Thanks for your help

MG

 

Hi,

Welcome to the forum.

Sure other will have differing views, but as your lawn sounds like it has been properly installed we would suggest for simplicity you place the raised bed onto the lawn rather than cut it up.
Any water from your bed should drain away normally though the lawn.

12" or deeper would be a good for most normal crops, so make up your raised bed place and just place it on the lawn..
You could put some breathable membrane in the base so the grass will stay a clean as possible should you ever move the bed.
Staple any form of polythene/ rubble sacks to the inside of your frame to help lengthen the life of it and save any soil or water from exiting via the joints etc.

We would add an inch or two of soil then all of your garden compost and topped up by the rest of the soil etc, keep some in reserve as it will settle quiet bit.

The compost worms will not thrive as such, they need that kind of wet veg.
Just add some normal garden soil to your bed and that should start the normal soil worms off.

Keep your beds to 4ft or under wide, that allows you to easily reach the middle of the bed from either side without needing to step on it.

You could also add corner posts so you could easily add crop protection netting when needed.

 

Thanks for the advice.

Here's how it's going so far.

The old floor boards and some shelves (soft wood) have made a bed 35cm deep by 178cm long and 109cm wide. These measurements are only due to optimising the use of scrap wood rather than a design specification.

Corner posts are from a for-sale sign that fell into my front garden a while ago. I thought about the idea of having the posts sticking up above to mount protection but decided i can always add taller posts on the outside easily and would prefer them out of the way.

I have some fence paint/stain. So i'll paint the wood then use an old tent ground sheet cut into sections to line the sides and protect the soil from the paint and also wood from the soil. Since the wood is already treated/stained i'll need to do this anyway.

To stop the frame walking about on the lawn during the initial loading with soil my plan is to screw long wood screws into the bottom face of the edges/corners so that they stick out like spikes, then dremel the heads off so they will stick into the lawn. yes this will damage the membrane but i'm not precious about this.

I've attached (no i haven't, it seems i can't add links yet) a picture of the bed as built with no treatment yet, it's bigger than it looks. note that the slight bend in the right hand side is real and due to the lower board on that side being warped. Only a cosmetic issue. The diagonal measurements are only 2cm different, so it's ok.

The way to find a picture is to search Google for "flickr Master Grunthos", it's then the first image on my rarely used Flickr account.

Cheers

MG