[JTh]

The solarization sounds very interesting, I would like to try it if I should expand the cultivated area in Greece (I don’t think it would be hot enough here in Norway). For perennial weeds with deep roots it may not be efficient enough, though, I read that the root system of Bermuda grass can grow to over 2 m deep, so maybe Roundup may be a better solution in that case, and also if you have problems with couch grass  (Elytrigia repens), which I have a lot of.

[ezeiza]

Again, since it seems you do not read my postings in full. If it is airtight as it should the heat chamber will exhaust even deep rooting plants like Bermuda grasss.

[JTh]

I am all for avoiding the use of chemical weed-killers as much as possible, and there is no doubt that solarization increases the soil temperature and can be a useful tool to reduce pests of various kinds, but when reading the literature, there is a lot of evidence that the effect is greater in the upper layers of the soil.
In an article by Horowitz et al. (Weed Science © 1983) they write that the heating effect from solarization decreased with soil depth, and that established perennials escaped the treatment. There is a review by B.M. Chittapur. (Agric. Rev., 23 (3) : 202 - 207, 2002. Soil solarization-temperature dynamics of soil) where ‘the typical soil temperature at 5 cm under clear polyethylene was 49-57 °C at mid-day’, the highest temperature cited was 60.7 °C, but also that ‘It is a proven feature that with increases in soil depth the maximal soil temperature attained through solarisation decreases --- at a depth of 30 cm or more, the rise in soil temperature is greatly reduced’.

[ezeiza]

A paper is not the revealed truth, anywhere, and it only reflects on many occasions, the results of an experiment. Why to decide if solarization is good or not based on a paper? It is amazing. We have been doing it for years and it kills perennial plants, only that the process is longer. No chemicals, no expense and the plastic can be used over and over. For larger surfaces we had even used the brand new plastic in rolls that was destined for new greenhouses without even having to cut it in pieces.

[andrewsloan]

This has been a very interesting discussion for me. I am going to experiment using Round-Up in on area and solarization in another as I really like the idea of using the strong sun here in the summer in my favour. If I find that when I take the black plastic sheet off the vegetable garden with the cardboard and compost underneath, that the Bermuda grass is still growing there, then I shall solarize the area for 2 weeks as you describe Ezeiza.

[ezeiza]

It is a method that has been used for years with excellent results. Remember (sorry for being insistent) that the air chamber below the plastic must be air tight: if heat escapes through gaps results will not be the same. Literally, weeds must be roasted.

[andrewsloan]

I have read on another website that one should water the area before setting up the plastic and air tight chamber. Do you think this is necessary?

[ezeiza]

But, previous watering seems a nice way to provide an additional chance for survival of the same weed one wants to exterminate.

[andrewsloan]

I can report back on my progress with eliminating grass weeds as follows
1.I have used Roundup for a 75 sg mtr part of my bancal where I am making a dry garden, left it for 4 weeks and am now mixing in river sand for better drainage and no sign of weeds or grass so it seems to have worked well
2.I have used the solarisation method, following Ezeiza's instructions carefully particulary re the air chamber, in two places, a flat area of approx 30sq mtr and a smaller area next to some steps which had 3 different levels. The flat area was easier to set up and to put earth around the side of the plastic sheet to seal the air chamber and after leaving the sheet for 4 weeks I have taken it off and it is a weed free area!
The other area I don't think was sealed properly as the Bermuda grass has continued to prosper. It seems more difficult to close off an area under the plastic which is not flat, so I think it was my fault in setting it up rather than whether the solarisation process works, as it did do do in the flat area.
I have enjoyed experimenting and will continue to use my plastic sheet for flat areas that I can seal off and use the Roundup for other, more difficult areas.

[Alisdair]

A really helpful experiment, Andrew; thanks!
Great to have confirmation that the solarisation method works so well.

[ritamax]

This conversation is important! There is a very good guideline to gardening: DO NO HARM! I don't believe, that we as private gardeners, not depending financially from our gardening product, have any right to put any toxic substances out in the nature. With the ecological problems worldwide we just cannot afford to do that. The only rational thing is to support the local ecosystem and garden as naturally as possible. One can weed by hand, remove aphids, slugs etc. by hand. There are plenty of good non-toxic methods against pests: water, oil, soap, baking soda, milk, garlic, partner planting, cleaning out the debris, using clean mulch etc. I think we should not cling to any sick plants and try to save them with toxic substances. We should exchange more about the methods, which really work. 

[ritamax]

OK for me. I would find it helpful to get more information, what is toxic and what is not. There are some traditional methods, which claim to be safe, but are not. Or new substances come to the market and are they safe to the pollinators.