How to measure fertilizer?

wasabi_VA(7)April 1, 2011

I had a soil test done by my extension office. The recommendation came back to "Apply 4 lbs (8 cups) of 5-10-5 per 100 square feet.

Does 8 cups actually weight 4 lbs? Do they literally mean use something akin to a measuring cup and spread out 8 cups? Or distribute 4 lbs? Those are equivalent measures?

I have a 20x20 garden, or 400 sq ft. Do I go shopping for a 20 lb bag of 5-10-5 and spread 75% of it evenly over my garden?

Thanks- real rookie here!

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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

8 cups = 1 lb. is just an estimate. One is a measure of volume and the other a measure of weight. So how many cups = a lb. all depends on what is being measured. ie. 2 cups of sugar = 1 lb. but it takes 4 cups of flour to = a pound.

You can use 8 cups if you wish but it is easier to use a 1 lb. coffee can if you have or can get one since coffee approximates granular fertilizer in weight.


    Bookmark   April 1, 2011 at 4:05PM
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I don't want to over fertilize. Not sure if I should use 4 lbs or 8 cups. They just do not seem equivalent to me.

    Bookmark   April 1, 2011 at 4:11PM
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By using 5-10-5 you will not over fertilize. Also 2 cups = 1 LB. I just checked it on my vegetable scale. There for 8 cups = 4 LBS. Hope this helps.

    Bookmark   April 1, 2011 at 5:12PM
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The recommendation came back to "Apply 4 lbs (8 cups) of 5-10-5 per 100 square feet.

20 foot by 20foot = 400 sq. feet. Buy the 20 lb bag and spread 16 lbs evenly over your whole garden and work it in good.

    Bookmark   April 1, 2011 at 6:23PM
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seysonn(8a WA/HZ 1)

I would never apply that much dosage in one application.
I would rather do it twice,each time half of that amount, the second time after a month or later. I use one bag of 10-10-10 and one bag of urea for about two years and I have over 800Sq-ft.I also add compost , leaves, straw etc.
MAYBE your soil is REALY POOR.

    Bookmark   April 1, 2011 at 9:09PM
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Thanks everybody. MrDoItAll has confirmed the weight for me - it just sounded high. I have already planted a few things (potatoes, sugar pees, onions, lettuces) with some showing above the ground and some not yet. Is it still OK to scatter the 5-10-5 on the surface if I have already planted? I will not be able to work it into the soil or I risk disturbing my plants.

    Bookmark   April 2, 2011 at 9:22AM
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Dan Staley

You want to work it in as some nutrients are immobile in soil.


    Bookmark   April 2, 2011 at 9:58AM
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Isn't this waste of money. you are feeding the weeds. I am sure you have great weeds. I apply Fertilizer drictly to the plants. 4 inches away from the roots. For vegetables I use 10-10-10. For trees I use 16-4-8 the slow release one.

    Bookmark   April 2, 2011 at 10:07AM
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Beeone(4 N. Wyo.)

Your fertilizer recommendation amounts to only 87 lbs/acre, which is plenty but not excessive. It all depends on how fertile your soil is to begin with. Garden crops can easily remove nitrogen at a rate exceeding 150 lbs/acre. Still, there is no reason you have to apply it all at one time. Half now to get things going, another half in 6 to 8 weeks.

If you apply it shortly before a 1/4" to 1/2" rain is forecast, the rain will carry it into the ground. Urea nitrogen fertilizer, left on the soil surface can vaporize and be lost if not watered or worked in. Also, to work it in, just use a very shallow cultivation of the soil to mix the fertilizer in, you don't have to go deep, and you can stay a couple inches away from the plants.

Don't get the fertilizer on the leaves of plants already growing or the nitrogen will burn the leaves. Rather than broadcast it, with prill fertilizer you can take a handful and dribble it along/under the plants so that the prills average about 1/4 inch apart if broadcast in a band 3-4 inches wide. If you dribble a line, using an amount equivalent to what it takes to spread 3-4 inches wide, 2-3 inches from the plants, incorporate lightly. If you spread it under the plants, get it rained in or sprinkle the garden to carry the fertilizer in.

Phosphate (the 10 in 5-10-5) does not move well in the soil, however if your soil is acidic (under 7 pH) it will be more soluble and move deep enough for the plants. The nitrogen and potash will move easily with water--hence the reason you don't want to overfertilize and have it run off the surface or leach to groundwater.

    Bookmark   April 3, 2011 at 3:30AM
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I have mixed in about 200 to 300 pounds of compost and some manure *after* that soil analysis was performed. I am considering holding off on adding the 5-10-5 fertilizer since I've planted quite a few things already and instead retest the soil at the end of the season. Then I can add the fertilizer and till it in. Is this a good idea or will I have problems this growing season without adding the fertilizer?

    Bookmark   April 3, 2011 at 8:28AM
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300 pounds of compost-manure is roughly 4-1-3 by dry weight, which (you will have to judge how wet it was) may be 50% for "dry" compost. So you probably have put in 4 lbs of N, 1 of P, and 3 of K or close to it. But the reason you were told to put in 5-10-5 is that you are a bit poor in P.

So, at this point, you might want to buy a small bag of superphosphate. Being P, you can put it in all at once and forget about P for the rest of your gardening days, it will be there for years. K needs to be added more often (I add it once a year, plus the significant contributions from man-made urea) and N more often still (twice a year to several times a year, depending on the vegetable), so it makes no sense to fertilize for everything at once. OTOH, your fertilizer is in compost and will leach slowly. I think for this year you would be set with a little P.

    Bookmark   April 3, 2011 at 9:49PM
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