[andrewsloan]

There is an area of our garden of about 60 sq metres that we want to replant with dry garden waterwise plants. We have to improve the basic clay soil's drainage by mixing in a lot of river sand but we also have a lot of strong grassweed with a network of roots growing that I would like to eliminate. I am considering giving a spray of Roundup and leaving it for 3 months or of covering the soil with cardboard and then black plastic, something I am trying also for part of the vegetable garden and leave it for 6 months.
Any ideas or experience would be welcome.

[David Bracey]

Andrew my advice would be to use Round-up since it is very efficient, safe and inexpensive.  I assume your grass weed is Bermuda grass, Cynodon dactylon, but of course it may be something else.  Round-up will still work.

Let your weeds grow so that there is a good canopy.  This will include annuals and perennial weeds.  Spray Round-up , I think the rate is 1.4% for perennials in a high volume of water to ensure good wetting.  Allow the product to work, at least 3 to 4 weeks and wait for another flush of weeds.Do not disturb the soil as this will only make a seed bed for more annuals.  Again wait as long as practical and allow any remnants of grasses to grow away. Spray again.

The downside to this practice will be a baked hard soil since we are probably talking up to 12 weeks which will take you almost to the autumn rains,  Can you wait this long, if not try your other methods which will not very efficacious.

Of course you can forgo the follow-up treatment and get planting that much earlier. 

In general try to cut down on cultivations.  They produce seed beeds and weeds, destroy soil structure which leads to soil erosion and so forth.  I know plants "look" better after hoeing but I  think this is an optical illusion.  david

[JTh]

You write that you have a lot of strong grassweed with a network of roots growing; if some of this should be wild oats (Avena fatua), then it may not be so easy to get rid of this; we have a lot of it in our garden in Halidiki, and it is a constant fight. The seeds may survive in the soil for many years, in an article I read several years ago about seed longevity, Miller & Nalewaja found that several wild oats seeds were viable even 168 months (=14 years) after burial, see http://www.jstor.org/discover/10.2307/3987500?uid=3738744&uid=2129&uid=2&uid=70&uid=4&sid=47698838827427.

I have covered some weedy areas in my garden in Norway with newspaper plus a layer of weed-free soil on top and grown vegetables right away, it has worked pretty well (until the weeds come creeping in from all sides again).

[David Bracey]

Wild oats are one of the worlds top ten weeds.  Try minimum cultivation in your garden.  Each time you cultivate you will bring up new seeds in the seed bed you have prepared for them.  It is virtually impossible to eliminate  them due to their longevity and numbers.

[JTh]

In Norway we have a special wild oats regulation and those producing grains are obliged by law to perform annual checks. I was very surprised when I asked a neighbouring farmer in Greece if there were any such rules; he wondered why I asked and said he could not understand why I had anything against it, since it had so many positive medicinal properties.

I only weed by hand, but I guess it will take a lot of years to deplete the supply of seeds. On the other hand, I actually enjoy weeding, I find it very soothing, but there are limits!

[Alisdair]

We find that during the growing seasons in our part of Greece wild oats are quite easy to pull by hand, but you have to destroy the plants carefully, as the green "unripe" seeds are already viable and have not yet entered dormancy, so germinate quickly if you drop them. We don't have too many, but they seem to be topped up constantly by supplies that I think come from our close neighbour's chicken run.

[ezeiza]

A perhaps dumb question as it is not a serious weed here: what if you weed them BEFORE seed production and use it as a (light) mulching in the same bed? Since it is so abundant it would ultimately become a source of organic matter.

[andrewsloan]

David the grass weeds are indeed Cynodon Dactylon. I agree with you and shall probably go for the Roundup treatment several times as you say. I suppose it would be better to do that starting asap and then mix the river sand in to improve drainage in the autumn and plant after that, although this February's unusually cold spell in Andalucia is encouraging me to wait until the Spring which leaves plenty of time to try and eliminate the Bermuda grass.

[David Bracey]

Spring is here.  I think the key now is to get a good stand of weeds and hit them.  I would also spread any sand asap and let it commnce working itself into the soil.. Mix in the sand when you start your soil preparation, keep your operations to a minimum .  It will help retain moisture as well.

[Ina]

I think round up is the best solution... although I prefere to avoid chemical treatment when it is possible. you dont have to buy round up, you can use any pestiside with glyphosate 36%. there is also round up max with 68% glyphosate. for Cynodon dactylon you should use around 750ml in 30L of water. this dosage is for 1000sqm.

[ritamax]

We had 250 sq meters of Bermuda grass with all possible weeds, as we bought our house in Costa Blanca South (very arid, dry climate). The soil was baked, dry and compacted clay with sand and stones. We had 4 people working with all possible instruments and got everything out as well as we could without any chemistry. After that we put a permeable weed membrane (plastic should also do, would be probably even more effective and is of course much cheaper), stone chippings on the membrane and it is working very well. The weeds come very little through, practically only on the sides and are quite easy to remove. I think weeding is a part of mediterranean garden practice! I am happy, that we didn't use any weed killers!

[ezeiza]

Roundup under controlled conditions have very low environmental impact.

For a small area like that mentioned you could try solarization. This involves covering the area with transparent plastic. The plastic should be actually separated from the ground surface by some 10 cm.: this is easy to obtain by placing bricks on their sides, logs, etc. at strategic points. Esentially, there should be an air chamber exposed to the sun under the plastic. The plastic edges should be covered with soil to avoid air escaping through any gap. What you obtain is a furnace where temperatures will rise greatly without heat loss and this of course will roast any weed or plant under it. It is very effective. Deprived of rain or dew and at the same time exposed to intolerable heat will of course take care of any plant you want to erradicate.

[andrewsloan]

Ezeiza, very interesting what you recommend. How long would it take do you think? I am doing something similar in half of my vegetable patch by covering it with a good layer of compost and worm manure, then a layer of cardboard and on top a black plastic sheet held down at the sides. That should kill off the weeds and leave a lovely rich surface on which to plant vegetables in the autumn.

[ezeiza]

If it is air tight and the sun strong enough in two weeks there should be nothing alive inside it. Annuals and perennials without deeply creeping rhizomes are cooked for good in a matter of few days but grasses like Bermuda will keep on making attempts and will be consequently killed. Your method is excellent for improving soil quality but basically you will be left with the same (or more) rhizomes than at the beginning. But, it is important that the air chamber is present under the plastic for effective solarization.

[David Bracey]

I first saw solarization in California in 1967.  It is a practical method for controlling weeds, especially annual weeds on a small area.  It is also effective on many soil diseases.  Generally it is works well down to 10 to 15cm however Bermuda grass will come from below this level.