A common mistake by many lawn novices is to head to the green shed and buy a bottle of weed and feed. I mean the name says it all, it will kill my weeds and feed my lawn in one easy step, right?
Not exactly and to understand why, we need to have a look at the product analysis. A 2L bottle of the average Weed and Feed contains 11.5% Nitrogen (mostly from Urea), 0.13% Iron, 15g/L MCPA and 2.3g/L Dicamba. The bottle states this will cover 130sqm.
In 2L, this is the equivalent of around 56ml of an 80g/L Dicamba based herbicide, 500g of Urea, a little Iron Chelate and the rest of the bottle is water. You are then further diluting the product when you hose it on.
The recommended rate of most Dicamba herbicides is 65ml per 100m2 (84.5ml for 130m2) so we can immediately see that it is well short of the recommended rate without factoring in the dilution from applying with a hose on sprayer and the fact it will be applied with very large water droplets so likely washed off the leaf and in to the soil where absorption is not optimal.
On the "feed" front, 500g of Urea will provide a quick boost of growth and the iron will improve the colour slightly but it will be all over within 1-2 weeks.
If we were to compare the cost per application (over 150m2) to Contra M Duo at $3.60 and Special Fex at $9 (300ml rate when buying 2.5L), the total being a bit over $12, it is much better value than the near $20 for the weed and feed product, which is also a much lower strength.
If we want to look even further at the economy side of things, as little as 500g of 2Spec Elevate will provide the same 115g of Nitrogen however will release it much slower meaning it feeds it for longer. While I wouldn't recommend applying rates of granular this low, 2kg to cover 100m2 costs $7.65 if buying a bag and when we add on the $3.60 worth of herbicide, it's about half the price of the weed and feed products and will feed it for 2 months rather than 2 weeks.
So please, if you want better results and to save some money, keep the weeding and feeding separate.