Let's start at the beginning.
About two years ago, the lawn in our back garden was full of dandelions. We decided to replace it with brand new turf, the
kind you roll out into place. I tried my best to remove the
dandelions, tap-root and all.
It sounds like the ground wasn't properly prepped. New sod should go onto a freshly worked bed of topsoil, with no living plant matter in it (this interferes with the new roots, and sometimes weeds will grow through the new sod, causing problems. As you wouldn't want to use an herbicide, you would have had to peel (or cut/dig, if there wasn't a good root system) off the existing lawn, leaving as much topsoil as possible on the ground. Or you can use an organic herbicide, however, these are expensive and most have mixed reviews. More than 1 application may be necessary.
After that, you would want to work the ground, using a hand tool (spade or garden fork), or to save time and your back, a tiller. You should be able to rent one if you don't own one already.
You want to break up the top layer of ground very well, but not go too deep, because you are going to be walking on the new sod, and you don't want footprints or uneven settling.
If all you did was remove dandelions, that explains why the sod did poorly.
There are large patches of clover, and another weed that produce rather nice and very tiny purple flowers.
Clover will only outcompete grass where there is a lack of nitrogen. In a healthy lawn, clover may come up, but even in a patch of it, there will be more grass than clover. This is because clover produces it's own nitrogen, and can fill out in the weakened grass.
If the "weed that produce rather nice and very tiny purple flowers." looks like this, it is creeping charlie, which signifies too low of a PH.
Where there is grass, most of it is dead (brown and straw-like), or it's twice the height of everything else.
If this occurred within 4 months of laying out the sod, it was from improper ground prep and/or watering, or from low mowing in dry weather. Lawn grass actually prefers higher to lower in mowing height. If some of the grass is twice the height of the other plants in your lawn, this suggests too infrequent of mowing. You should mow whenever the grass gets over 2 inches higher than your blades are set, for best results.
I accept that I will probably have to start over, but before I do that, I would like to know what I can do to reduce the
chance of this happening again.
If you are going to do this without chemicals, you should expect to put lots of time and effort into your lawn. To reduce the chance of this happening again, you will have to provide conditions in which the grass will thrive.
If you are going to re-lay sod, you have to prep the ground as described above. Make sure there are no rocks larger than 2" across on the surface of the ground. Do not prep if the ground is wet enough to clump together. Even the ground out, so there are no dips where water could puddle.
When you roll out the sod, do not stretch it. Place the strips as close as possible to each other, but don't cause ripples. Once the sod is all laid, take a hose and water in the seams until the soil underneath becomes soft mud. Tamp firmly (but not violently) along the seams, so that the edges mesh together, and there are no air pockets under the sod.
Then you should water down the rest of the sod, but don't make this quite so wet. Only enough that the sod will establish a full contact with the soil beneath, without air pockets. The entire lawn should then be pressed down, either by rolling (preferable), or by light tamping.
The lawn should not be allowed to dry after this, until the sod has rooted and took off growing. Foot traffic should be kept to a minimum, and if the grass grows before well rooted, mow carefully with the lightest weight lawn mower you have access to.
You will also want to use some type of fertilizer, if you don't want the weeds to take over. The best high-nitrogen fertilizer for an all-natural lawn is blood meal. You can start applying this when the sod has rooted.
Also, in the future you will want to water your lawn whenever it gets dry, before it turns brown/yellow. Mow your lawn frequently, and set the deck high. This reduces plant shock, and drought resistance. The roots mirror what the top-growth is doing, so a very short lawn = very short roots.
You will also want to add soil helpers to the ground before laying sod. More on that under the next heading.
Grass also performs best at a ph of between 6.5 and 7. Get your soil tested, and add lime to sweeten the soil to right level.
I read somewhere that weeds tend to grow in places where grasses find it hard to grow. Does that mean my soil needs treatment?
If so, with what?
That is correct. A thriving lawn will out-compete most weeds. If your soil is really shallow and sandy, you will want to add to it for best results. You have a couple of options here. You can:
- get some high-quality topsoil dumped on your lawn, to create a suitable layer (at least 6") for the grass-this includes the existing topsoil in your yard
- try to build on the soil you have-buy lots of compost or similar product with a high organic matter content and dig them in, to a depth of at least 6"
When I dig up the soil, in places there's about 5cm of soil, and then nothing but sand. Is that a problem?
Yes, that is a big problem. You cannot grow a lawn on that shallow of soil. Also, sand is drying, and the lawn will constantly dry. Also, fertilizer will wash out quickly, before the grass can utilize it. You should have at least 6" of good topsoil on there, and 8-10 would be even closer to ideal.
I'm only interested in non-chemicals/organic solutions
This will make a good lawn difficult, but not impossible. The main difficulty will be weed control. Even If the lawn is very healthy, you will almost inevitably find dandelions, clover, and other weeds in your lawn, and you will have do remove them the best you can by hand.
Fertilizing is another factor you can't miss. With your sand subsoil, nutrients will leach quickly, and you will have to fertilize often. There are many nutrients lawns need to thrive, but their biggest one is nitrogen. blood meal is a fast acting high nitrogen organic fertilizer, and hoof and horn meal is a slow acting high nitrogen fertilizer.
You may want to consider using one of the many pre-mixed, balanced all-natural lawn fertilizers available on the market today.
Note: I only used this method on lawns which were either extremely sloped, or got washed out easily, or there is going to be foot traffic from pets/wildlife. Sod discourages digging. Generally I will use seed under straw mats.
Update in response to updated question:
I don't mow that often because our lawn mower isn't adjustable, and tends to cut quite short.
You will not be able to grow a vigorous, healthy lawn with a lawn mower like that. I would be surprised if there is really no way to raise the deck, but if that is the case, I would highly recommend looking for a new mower.
Also, letting the lawn go for a while, then mowing short, is very hard on even a healthy lawn. Short term, I would be better for the grass to be kept too short, rather than growing out in between.
Moreover, when I laid the turf I ended up with bumps. Only a few, but as you can imagine, the mower takes them right off.
A properly prepped lawn will not be lumpy after the sod is laid. If you level out the ground properly, you should not have this problem. Here's one thing you can try. After working the ground/adding topsoil, but before laying sod, you can use a lawn roller to roll out lumps. Then it will be easier to see the low spots/ high spots, and these can be corrected with a garden rake. roll a second time, and then rake the surface lightly to loosen up the surface soil.
Is your lawnmower a one blade walk-behind/push mower? If so, you can push down on the handlebar, to raise the deck slightly as you approach a lump/high spot. Or if you are able, you can do this over your entire lawn. From what I can see, this isn't a very large lawn. If you are using a riding mower, you will have to put up with a damaged lawn until you can get a new mower.
Also, there are patches where what looks like grass grows really fast, while the rest stagnates.
This could be caused by several factors, but the most common one is inconsistent soil depth, or fertility. It is also much more common in close-mowed lawns, because these grow much faster than higher lawns, and slight differences in the soil will cause big differences in growth. Areas of sod which did not root well originally will often grow poorly for a long time. Different types of lawn grass will grow at different rates as well.
Again, if you can find a way to mow higher, and if you fertilize properly, this symptom will go away.
Update in response to comments:
When is the best time to add topsoil?
You should add the topsoil soon before you lay the sod, so it doesn't get rained on. The best time to sod is in the spring after the frost is mostly out. It can be done in fall, but the results are not as good as fall-sown seed.
If you add the topsoil, and it rains, you will have to wait until the ground dries, and then work the ground up a little, and re-level.
Should I remove the current "grass" first, or just dump it on top?
If you are putting on more than 2 inches (5cm) of topsoil, you do not necessarily have to remove the existing "lawn". However, If you don't remove the existing vegetation and work the ground a little before adding new topsoil, weeds growing through the new sod will be a little more of an issue.
If you have a string trimmer, 'trimming' the grass into the ground before adding new soil will help.
Is it the same process for re-seeding?
The process for reseeding is very similar, regarding soil requirements. Neither one will do as well in soil worked extremely deeply, because this causes issues when settling, and later, when mowing or walking across the ground. New grass wants a firm soil, but which is loosened in the top 1-2 inches (about 2-5cm). This can be done with a garden rake after rolling.
Your lawn is going to be a challenge, but you can definitely do it, and well at that. All it takes is patience, energy, time, and some $$. :)