# 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.

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.

thanks for the information, anything new on the market to combat Chickweed?