Brianosauras
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Joined: Tue Mar 15, 2016 7:09 pm

Need help with Fertilizer or Soil Amendments please

Last year I built a raised bed box that is 4'W x 15'L x 2.5'H. I built it quite high because not only do I not with to bend over, but primarily because we had many yards of topsoil left over from another yard project.

I know topsoil is not a compatible soil for a vegetable garden and when we filled the box I planned on using it as base material and then finishing off with what ever is required.

I just used a home soil test kit on the top soil that is currently in the bed. Results were the amount of Nitro was "Insignificant" , Phosphate was also "Insignificant", and Potash was "Normal".

Can I try to fertilize the current soil with something like a 12-10-5 plant food or will not be sufficient enough?
Is there anything I can add that wouldn't be too costly to correct the problem?

I assume the other much more expensive option is to add several more inches of bagged garden soil to the 60sq ft box?

Looking to transplant my indoor seedlings in a few weeks and any help would be great. Thanks

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GardenThrive
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Location: Central Alabama

In my experience those diy soil test kits are not very accurate. The soil may be better than you think. Lots of places do in depth soil tests where you give them a sample and get back a detailed report. Fairly inexpensive when you consider how much money it might save you in fertilizer/soil amendments. Don't know that you should throw down fertilizer so close to the time you're transplanting the seedlings. Some good composted manure might be a good option to mix in. A nursery near me carries a pelletized chicken manure that is high in nitrogen and doesn't burn plants.

imafan26
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Location: Hawaii, zone 12a 587 ft elev.

Actually, adding compost would be better than adding more soil. Compost will make the soil more workable and add moisture holding capacity. You will need to probably add 6-8 inches of compost and and work it into the bed at least to the same depth. Compost takes time and you will need to add I t continuously. Manures and organic fertilizers also take time, more than you have to fertilize the soil. It is good to add them, just don't expect them to be available for months or years. You can only add a small amount at a time since it is also very high in salt. If you are starting with subsoil with little or no organic matter, there won't be a lot of soil bacteria in it so organic fertilizers won't work all that well until the organic part is built up. Unfortunately you cannot do that in a day or a year. That is why it takes years to build a good organic soil.

I don't like over the counter kits myself.

A soil test would be the best way to get the right fertilizer and the amount you should add. They are not costly and you can get them from your local university extension in the U.S.

Nitrogen will always have to be added no matter what since it is easily lost.

If your soil had something growing on it before, it cannot be all that bad, however if you moved a lot of earth only the top few inches was topsoil, the rest was subsoil and would have less organic matter.

Any plant food is better than nothing. It all depends on what you are growing. If you have light feeders they won't need much but if you are growing tomatoes, they are heavy feeders. I would go more with a balanced fertilizer like 14-14-14 or 10-10-10. The application rate would be 0.2 lb N per 100 sq ft. Your bed is 60 sq ft. so you would need 0.12 lbs N for the bed as a starter. If the Nitrogen is 10% in your bag of fertilizer that means that for every 100 lbs of fertilizer you will have 10 lbs of N. , you would need 1.25 lbs of complete fertilizer. Nitrogen as I said is easily lost. Phosphorus and potassium are not as mobile so it is better if they are mixed into the soil to start with. Nitrogen should be side dressed depending on your crop. but I use about a tablespoon of sulfate of ammonia or a teaspoon of urea per plant scratched into the soil or banded when the first flowers appear and again when the first fruit starts to form. Sulfate of ammonia is 21-0-0. Urea is 46-0-0. A good scale is a good investment otherwise you will have to figure out how much a cup weighs. Sulfate of ammonia is 0.6 lb per cup, but it is 20% N not 10% so you would need twice as much assuming your fertilizer weighs about the same. A guess on my part would be about 3 cups of complete fertilizer with 10% N for your 60sq ft plot assuming your soil is very low in organic matter.
https://www.ext.colostate.edu/mg/Gardennotes/711.html

Mind boggling. My home garden soil is high in everything including nitrogen judging by the size of the plants and it is acidic with a pH 6.4. I am using 1/4-1/2 cup of sulfate of ammonia per 100 sq ft. as a preplant with no side dressings and I am still getting monsters so I actually need to reduce the amount I am using more.



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