I had a bit of a mental setback a few days ago. I couldn’t resist doing a google search on what the effects were of asphalt on one’s health. You see, I had just set up our raised beds on cardboard on top of very old – what once was – asphalt (I think). I had filled them with dirt and at that point I decided to find out if it was safe to grow food like that. A little too late, but before I knew it I was typing out A S P H A L T in google.

And guess what, asphalt turns out to be not so healthy. They bring it in connection to leukaemia. Not all asphalt, the old kind of asphalt especially. In some countries this classic type of asphalt has been banned in the ’90 for that reason, but not in every country and in a lot of personal driveway cases (like ours), the asphalt is very old. As in before the ’90 probably. Bummer.

When a seed like this is planted in my head, I can’t let go. Even though I’ve read that the chances are very small that the chemical process takes place in between asphalt and a plant, and that it happens in a very slow process at a slow rate, only at very high temperatures apparently. Actually it’s the same chemical process that takes place when you heat olive oil at a too high temperature and when meat fat drips on top of warm coal of the BBQ. Knowledge, pfff, sometimes it’s better to be ignorant I think. Or just believe in an almighty god that will do as he/she wishes. There is so much we don’t know and can’t know. And even worse, even if we know, we aren’t able to act on it in problem solving way.

building up high raised gardenBut I knew this now and I couldn’t ignore it. So I spend a day thinking about a solution. I really want to grow my food, but not at all cost obviously. My idea was that I wanted to do two things to minimise the risk:

  1. I wanted to keep the asphalt as cool as possible, because transmission happens mostly when the asphalt is very hot
  2. I wanted to create a barrier between the asphalt and the plant (root/leaves), as the chemical reaction takes place most often when direct contact is possible


So I went to the DIY store in the morning with some vague ideas and came back with practical materials that would help me with the two prerequisites I had set out. But first I had to dismantle the setup that I already made (the one that you see above). Quite some work before I could start covering everything up again. After two hours of dismantling, I was ready to move on. Step by step.

STEP 1 After I took everything away, I laid out more cardboard. A thicker layer of cardboard. I now also laid it out on the surfaces in between the boxes. The idea was that this would cool down the soil in first instance and create a first (temporary) barrier. I chose for a temporary layer, because we are renting this place. So chances are that we won’t stay here for a really long time. And ideally this cardboard will be eaten away by nature when we dismantle the thing.
building up high raised garden

STEP 2 I chose bamboo sheets for layer two. I doubted a lot about this step. These sheets aren’t made as flooring, you see. So they are very fragile in many ways. At first I wanted to lay out a whole sheet of (food safe) black plastic, to really cover everything. But that wouldn’t work with my idea of keeping everything as cool as possible when the sun is burning. Bamboo on the other hand in combination with the cardboard would. Also, plastic will tear up and break as well, I know from experience and there is nothing worse than clearing up small pieces of plastic from an area. Bamboo is just a natural material, so it won’t be necessary to clean up all the small pieces that fall off. building up high raised garden

STEP 3 Now that I had arranged the cooling down part. I had to start working on my second prerequisite: creating a barrier between the asphalt, the plants and the soil in which they grow. I bought wooden walking boards/tiles (I don’t know how you call them in English actually) for this step. They had them in several sizes and these two sizes worked perfectly with my boxes. They are about 2,5cm high. Pallets would work well for this step. I couldn’t get my hands on those and they were pretty clumsy for moving them around if we move. These tiles are very practical for that reason.

building up high raised garden

STEP 4 By now it was slowly getting dark. It had been a long day, but I really wanted to set up the boxes again. So that’s what I did. I carefully placed everything back on top of the tiles.building up high raised garden

And that’s where I am today. This morning. There are few more things I have to do to make it ready for planting. I will lay out a sheet of (food safe) plastic on the bottom of every box and then I will have a second layer of (perforated) (food safe) plastic as a bag underneath the soil that I will bring back in. I will also add a few walking boards as a cross between the boxes. To keep the bamboo a bit more protected. And then I will probably add a layer of wood chips as mulch around the outside of this area. That’s it. I initially thought this was going to be much more work. But with a bit of concentration and effort, I made it work in a long afternoon. Not bad.

I feel comfortable about growing food like this. There is a tiny chance that the hot asphalt will touch the plants this way. I will also make sure that the plants will not fall out of the boxes. I joked to Eduard that this setup will be almost as clean as a cleanroom in his lab. Which it isn’t obviously.

Anyway, come back next week, to see how I’ve cleared this whole mess up and made the boxes ready for growing food.

building up high raised garden by pakovska