How to Calibrate Your Fertiliser Spreader

When using a mechanical spreader to help distribute granular fertiliser across your lawn or sports ground, it’s really important to make sure you calibrate your spreader correctly. If you fail to do this, you could end up using too little fertiliser, meaning you don’t get the results you were hoping for, or even worse, you could apply too much fertiliser and end up damaging or even killing your grass.

Types of spreader

There are two main types of spreader people commonly use at home, drop spreaders and broadcast spreaders (sometimes called rotary spreaders). A broadcast spreader contains a rotating plate connected to the wheels which is driven round as you push the spreader along. This throws out the fertiliser in a circular pattern around the spreader, allowing you to quickly cover a relatively large area. This makes broadcast spreaders well suited to bigger spaces.

Drop spreaders use a simpler trough-like design, with holes in the bottom that allow the fertiliser to drop onto the grass. This gravity-fed design is better for smaller lawns as they allow a more precise application of fertiliser, but achieve a much slower rate of dispersal than broadcast spreaders.

Both types of spreader can usually be adjusted to control the rate at which they distribute fertiliser which is vital for achieving the correct spread rate.

Calibrating your spreader

Although the designs are different, the basic method for working out the rate at which your spreader distributes fertiliser is the same for both types. To do this you will need:

• A tape measure

• A bowl or jug

• A set of scales

• Chalk or pegs and garden string (optional)

 Step 1 – Working out your test area

 Most lawn fertilisers will give a distribution rate in grams per square metre (although products for larger areas, such as sports fields and pony paddocks may be in kilograms per hectare). To calibrate you spreader, use your tape measure to mark out a test area – we recommend using at least 10 square metres initially. You can use part of your lawn for this, but it may be safer to start off on a slabbed or tarmacked area so you don’t risk damaging your lawn and can easily sweep up the fertiliser after you’ve performed your calibration testing.

 Depending on where you are running your test, you can either mark out the area with chalk or pegs and garden string, or else use reference points such as the edge of slabs to keep a rough idea of the area. However bear in mind that the more accurately you can determine the test area, the better the results you are likely to achieve.

 Step 2 – Preparing your spreader

Weigh out the required amount of fertiliser using your scales and a bowl or jug as a container. For example, if your fertiliser has a recommended spread rate of 35g/m² and your test area is 10 square metres, you will want to measure out 350g of fertiliser. We recommend doubling this amount for the test, however, as this will make it easier to work out if you are distributing at too fast a rate. Place this fertiliser into your spreader (with the distribution holes closed!) and move the spreader to a couple of metres from the start point of your test area.

Step 3 – Testing your spreader

Walk at a normal pace pushing your spreader in front of you. When you reach the start of the test area open the distribution holes to the middle setting and continue to walk at the same pace. Move up and down the test area making sure to close the distribution holes when turning to avoid spreading too much product. Try to maintain a steady pace throughout the test and avoid going back over the same areas twice.

Step 4 – The calibration

Once you’ve covered the entire test area, you need to check how much fertiliser you have left in your spreader. Carefully scoop or pour the remaining product back into your measuring jug or bowl and weigh this on your scales. By subtracting the amount of fertiliser left from what you had at the start you can work out if you were spreading it too fast, too slow or just right. If your initial rate was wrong, rerun the test with a higher or lower distribution setting as required. Keep running the test at different settings until you achieve the correct spread rate and then make a note of this setting for future reference.

And there you have it. You have now successfully calibrated your fertiliser spreader and can look forward to a green, healthy lawn in the near future!

For further advice about looking after your lawn, or to find out which of our lawn products are best suited to your needs, give us a call on 0117 311 1217 or why not Ask John?

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