Calculating Lawn Fertilizer – Family Plot


All right, Mr. D, let’s see if we can tackle
some garden math. – Gardening math, I hate math. (laughing) – I think we all concur. – Yeah, yeah. – But math is a big part of
putting down fertilizers, putting down pesticides, so
you have to know a little math. – (Mr. D)
That’s right, kids. – So, when they told you to pay
attention in algebra class– – You better do that. If you got it, you’re
gonna have to use it. – Yes, you’re gonna
have to use it. – Fortunately, we have
calculators nowadays. They help and there’re
a few apps out there that give you a little
bit of help, too. It’s good to be able
to know how to do it so you can kinda cross check, and make sure you got it right. It’s really important
that you do it right. And you might wanna,
like I said, double check because one little decimal
point can make a big difference. Two decimal points makes
a real big difference. If you’re supposed to get 10%, .01 instead of .1,
that’s very important. – (Chris)
Makes a difference, no doubt about that. – But the important thing
when a lot of the pesticides, and fertilizers, and
soil test reports, and things like that will break
homeowners information down to a thousand square
feet, or sometimes, per hundred square feet. Most of the time, it’s
per thousand square feet. So, probably the most important
thing you can do first is determine how many square
feet that you’re treating. And we all know that in
order to find the area of a rectangle, we multiply
the length times the width in feet, and it’ll give
you the square feet. Or in inches, it’ll give
you the square inches. If you have a lot, I
would determine the area of the lot first, and
then I would determine the area of your house,
and subtract that from your total square
footage of your lot. Measure the area of your
driveway, subtract that. Measure the area of your
patio, subtract that. The area of your dog
pen, subtract that. The area of your swimming
pool, subtract that. The area of your
workshop, subtract that. And when you’ve
done all of that, you will pretty
much have the area, the total area in square
footage that you’re treating. So, then you’ll know
how much product to buy. And then if you’re
using a fertilizer, keep in mind most of the soil
test reports will tell you how much nitrogen you need
per thousand square feet. They’re not gonna tell you
how much triple 15 you need, because you may
not have triple 15, you may have triple 10
or 6-12-12, or 34-0-0. Or there’s a lot of different
formulations of fertilizer, so they’re gonna tell you
how much active ingredient you need per
thousand square feet. And then when you
buy that product, whatever you come up with, if it calls for 10 pounds of nitrogen per
thousand square feet, and you’ve got a 34% product, then you’ve gotta
reduce the amount. You’re gonna increase
the total amount of the product you put
out to get that 34%. You gotta bring it down to 34%. Same way with the 10%,
triple 10 would be real easy. If you would need
to put 10 pounds of nitrogen per
thousand square feet, then you’re gonna put, if you have triple
10, be a hundred, like a hundred
pounds of triple 10 that you’re gonna
have to put out there. It’d be two bags of fertilizer. So, if it’s 50-pound bags. So, just double
check everything, use algebra, use your
algebraic expression. I have to write it
down and look at it. If I try to do it in my head, I’m gonna make a mess. So, write it down and then
cross multiply, cross check, and then make sure
you’ve got it right. You can add more, so
if you underestimate you can go back and
you can add more. But it’s pretty hard to take up if you put too much out there. And putting too much out
there with fertilizer, can contaminate
our water supplies, and it can create problems,
it can create algae blooms and things like that. Don’t feel like just because
you have a 50-pound bag of fertilizer you’ve
gotta use it all. It will keep, it will keep. You can roll it up and
put you some duct tape on it and use it next year. Just use what you need. And with herbicides,
if you put out more than you’re supposed to put out, you can kill desirable grass. Some of the herbicides may be
targeted to just broadleaves, but if you go a way, way, way
more than you’re supposed to, you might kill everything
that you’ve got out there. – (Chris)
For sure. – So, it’s important to
follow label directions and unfortunately,
you gotta use math. – Speaking of using math, you
wanna get to our math problem? – Well, let’s do a
math problem, yeah. – Let’s see if we
can do one quickly. – Okay. – So, set us up here,
what do we have? – Have I gotta show you my
scratchin’ here on this? I can do that, I can do that. What I’ve got here is
triple 15 fertilizer, and the soil test
recommendation calls for 10 pounds per
thousand square feet. So, I know that I
have 4,000 square feet that I need to treat. I’ve done all my subtractions, and additions, and
multiplications, and I’ve got a 4,000 square
feet I need to treat. So, I just set up an
algebraic expression. I got 10 pounds per
thousand square feet, I’ve got 4,000 square feet. So, four times 10 is 40 pounds. I need 40 pounds of nitrogen
on my 4,000 square feet. And I’m using triple 15, so
triple 15 is 15% nitrogen, 15% phosphorus and 15% potash. And so I got a 15%
material, so I set it up. 40 pounds is 15% of what? 40 pounds just happens
to be 15% of 266.66. So, I need 266.66 pounds
of triple 15 on that– – (Chris) 4,000. – (Mr. D.) 4,000 square feet. See, it’s a weak material, and the triple 15
is only, it’s 45%, now in that you’re also gettin’ the same amount of potassium, and the same amount
of phosphate. So, triple 15 is 45%
fertilizer, and 55%– – (Chris) Inert material. – Inert ingredients. – (Chris)
As they say, or ingredient. – So, there’s a lot of
fertilizer in there. 266 pounds, how many bags is it? That’s quite a
bit of fertilizer. – Yeah, and I think
they come in what? 40 maybe, 50 pound bags. – And 10 pounds of nitrogen
is a lot of nitrogen. I just threw that out there. It may be probably one
pound or one to three pounds is probably a more
common recommendation on nitrogen fertilizer. So, that was just an
example that I used. – And of course, we
know that nitrogen moves pretty quickly
through the soil. – Yeah, and you know
it’s gonna be there if it’s not encapsulated, if
it’s not slow-release form, it will be gone in
four to six weeks. You know, a lot of rain,
four weeks, six weeks. If there’s not too much rain,
four to six weeks it’s gone. – Your algebra teacher would
be proud of you, Mr. D. Thank you so much. – No, no, she wouldn’t. – Well, we appreciate
that math question for us. Thank you much. – Thank you much.

2 thoughts on “Calculating Lawn Fertilizer – Family Plot

  1. I never paid much attention to the ratios. I always used 1/2 a handful of each one, blood meal, bone meal, and potash. So, last year I sent in a soil sample to be tested. It came back that I needed 5 lbs of N every month, no p or k for 5 years. This year my garden wouldn't grow a squash even after adding a bunch of Nitrogen.

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