Coming home from the shows with bags full of leaflets is just the start of it. Staring in awe at a contractors huge new shiny collection of tines and rotors just adds more confusion. The dealer having you bamboozled with hundreds of options is not helping. There seems to be just too much choice; six, eight or ten rotors - but what size tedder do you really need?

The general law of boys toys being “the bigger it is the more it costs”, you might be tempted to save some cash and choose a tedder that is just big enough to do the job rather than a machine fit for the prairies. Getting the right size tedder is important, too big is a waste of money (and a liability in the wrong hands) whilst too small will give you all sorts of headaches.

How should you choose a grass tedder?

The number one factor in choosing a tedder, is your choice of mower. This has nothing to do with the colour, the brand or the dealer, although there might be some benefits in a one stop shop for service and parts. No, the critical issue is the mowing width and the swath width that the tedder is following. To clarify, this only really matters if you’re tedding grass to make good silage, not if your tedding grass to make hay. Because if you’re making hay then you’re going to be shaking out the crop more than once and therefore you’re going to be driving on the crop.

If you’re making, or trying to make, good silage then you really don’t want to be driving on the grass at all. Driving on a swath of fresh forage just introduces billions more “bad” bacteria that you really don’t want.

Why leave the grass in a swath if you’re trying to dry it out?

So why leave the grass in a swath at all, wouldn’t it make more sense to spread it out as quickly as possible - like directly from the back of the mower? Maybe, but it depends on lots of things, and I would really only recommend spreading it behind the mower in dry conditions for relatively light crops.

That probably sounds like madness but there is some method. In a lush heavy forage crop - like we grow in North West Europe, the climate means the base of the sward at the time of mowing is damp at best, but wet in most cases. Spreading grass out on this damp underlay just traps moisture and makes the whole drying process slower. Alternatively, if you leave the grass in a swath for a couple of hours, in the right conditions, the stubble will dry out and the surface of the swath will begin wilting.

Grass spread onto a dry stubble will wilt to the target dry matter much more quickly than if it were dumped straight onto a wet bed. Stubble height also has a role to play but that’s another story.

How many swaths per pass?

So your tedder is going to pick up a number of swaths and the tractor should be straddling a swath so the tyres stay on the stubble and off the grass. Unless the machine is off set, then it's going to be covering the same width either side of the tractor so it's going to be working an odd number of swaths. Your choices come down to 1, 3, 5, 7, or too many swaths.

You could overlap the tedding and go through some of the crop twice, but the trial results I’ve seen don’t show any significant advantage. A second pass really just increases the leaf losses and increases the risk of contamination. So with this in mind then it will probably be a fairly simple choice; just multiply your mower width by 3 or possibly 5 swaths?

Mowing combinations and tedders

The ideal width of tedder is not quite that simple. If your combination of mowers are all the same size - maybe front and back mowers both 3m wide, then it is fairly straight forward. A 9m working width tedder would suit 3 swaths from 3m mowers very nicely, but larger butterfly combinations often have wider rear mowers however you can still do some pretty simple maths. What is perhaps not so clear is the relationship between the speed of the mowers and the size of tedder you need.

Now imagine you have been running a 9m tedder behind a front and back mower combination but now you want to switch to a set of triple mowers. You might imagine the tedder just needs to run a bit faster and for maybe a bit longer to keep up right? Unfortunately I don’t agree, I don’t think the 9m tedder is going to do the job you want it too. That’s because what you are really trying to do is make consistent forage, and going faster or longer with the tedder is not going to do that.

Why tedder forward speed is so important.

The forward speed of the tedder is absolutely critical to the job it does. Move too quickly with the tedder and the chopper or baler driver behind you will know about it. Lumpy swaths are more about the speed of the tedder than the rake. But more importantly the speed of the tedder should be dictated by the drying of the crop. Earlier I described the theory of drying the stubble before the crop is spread out, well that is not going to be consistent if the tedder has to start right behind the mower in the morning, but then finishes 3 hours after it in the evening.

The tedder output needs to be matched to the mower output without compromising the forward speed.

What is the correct forward speed for a grass tedder?

The slower the better really, but there must be a realistic target speed. In some trial work, different rotor (or pto) speeds were compared along with different forward speeds. The rotors speed didn’t make much difference in the work quality, but the forward speed really did. In the Massey Ferguson trial, a forward speed of 6.5kph was found to be best. Obviously the weight of crop effects this but in my opinion this is can be increased to around 7.5kph with a maximum of 8kph without compromising quality of work.

Calculating the optimum tedder size.

If we know the maximum speed the tedder should travel, and we know that the tedder output should be the same as the mowers, in acres/hour, then we should be able to calculate how wide the tedder needs to be.

Two 3m wide mowers (front and rear) traveling at 12kph in a field 500m long will theoretically produce 48 swaths per hour. To spread these in an hour at 3 swaths per pass, a 9m tedder would need to travel at 8kph so this is a reasonable match.

Now change that for a set of triples traveling at the same 12kph, and they produce 72 swaths per hour. For a 9m tedder to spread these in one hour it too would need to travel at 12kph which is far too fast. However a tedder that takes 5 swaths working at 15m would only have to travel at 7.2kph to keep up. This is a much better solution.

Now this is all theoretical and I haven’t allowed for headland turns but I am assuming that the tedder turns at a slightly slower pace to the mowers. It might not be completely accurate, but the principal of trying to calculate the best solution can be helpful. Ultimately it’s a case of trying to take some of the guesswork out of it; trying to make some more educated decisions. And trying to make better silage.

If you want to discuss taking guesswork out of your silage making or would like to discuss any other aspects covered in this series, contact me at jeremy@silageconsultant.co.uk