Understanding Potting Soil

saoodhashimSeptember 29, 2013

Locally in Saudi Arabia, I dont have the many brands of potting soil that are available in US. I was trying to compare the composition of Miracle Gro Potting soil with one that is available locally. Miracle grow states that it has 0.21%:0.07%:0.14% NPK in the soil and it can last for upto 6 months.

Being a beginner gardener (starting off with container vegetable gardening) my question is as follows

Is this what is required for container vegetables like tomatoes, cucumbers, peppers, carrots, potatoes etc for the whole six months or do I need to add more fertilizer - as the plant grows - and how often?

Also can someone guide me as to how to relate this 0.21:0.07:0.14 to the normal 10-10-10 or 5-5-5 terminology used with fertilizers? One site said that miracle gro is actually 21-7-14. Is it really that way? And actually how much fertilizer to apply to the pot full of soil when actually applying it - either initially or when transplanting the seedlings or later as the time passes?

Would be highly indebted for any replies.


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Ohiofem(6a Ohio)

I answered some of your question in the other post you had about the slow growth of your tomatoes and peppers. You definitely need more fertilizer as I explained in that post. The ratio of fertilizer in your potting mix (0.21-0.07-0.14) is 3-1-2, which is the same as if you had added fertilizer that was 21-7-14. That is a better ratio than the 10-10-10 or 5-5-5, which are both 1-1-1 ratios. But, you need to add more fertilizer to your potting soil.

    Bookmark   September 29, 2013 at 12:17PM
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Thanks again for this reply.

But you did not tell how much should I apply and how should I apply? Sprinkle or dig etc.

    Bookmark   September 29, 2013 at 1:58PM
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Ohiofem(6a Ohio)

How much to add, when and how to add it all depend on which kind of fertilizer it is as well as how big your container is. An organic ingredient like composted manure is fairly safe to use in larger amounts. An inorganic fertilizer should give you some directions on how much to add on the package. Many I have available here call for about 1 tablespoon of fertilizer for each gallon of soil. For example, if your container holds about 10 gallons (35 liters) of soil, you could add a couple inches of composted cow manure and a cup (.25 liters) of dry fertilizer to the top of your container and gently mix it in to the potting soil around each plant being careful not to let it come in contact with the roots. This is assuming your fertilizer has a balanced ratio of NPK. That might be a start.

    Bookmark   September 29, 2013 at 3:19PM
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And how often should i apply this 2 inch application? Fortnightly? or monthly?

    Bookmark   September 29, 2013 at 10:26PM
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Ohiofem(6a Ohio)

Just add the layer of compost with fertilizer once. The compost will provide a little slow acting food for your plants. The fertilizer acts faster than compost. You said that the local nursery guys told you to add the fertilizer once a month by sprinkling it on the sides of the plant. (It should really be sprinkled on the edges of the pot. Don't let the fertilizer touch the plant.) I think you could add the fertilizer every two weeks because it sounds like the soil they sold you is not very fertile. Your plants would have grown several inches in the two weeks after planting if that soil had enough fertilizer in it. Since you haven't told us how big your pot is, I don't know how much you should use. Ask the nursery guys what they think.

    Bookmark   September 30, 2013 at 12:47AM
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Thanks again. You certainly have been a great help!

The pot size for tomatoes is 14" diameter and 12" depth (approx 5 gallon) and the pot size for pepper is 10" diameter and 10 inches depth (approx 4 gallon). Does that give you an idea as to how much fertlizer may be required?

While I was aware that the stem, leaves and roots should not come in direct contact with the fertilizer, however, I was also a bit concerned about the distance of the plant from the fertilizer. If I apply the fertilizer towards the edges of the 14" and 10" pots, wouldn't it delay the actual usage of the nutrients by the plant until the roots reach there? Especially when the manure compost acts slowly.

Btw, someone on this forum told me to use compost tea for fertlization. Can that diluted compost be watered in a similar fashion as the watering is done, or that too has to be on the pot edges? As I understand, when watered with compost tea, there is no need for separate watering at least for that day.

Sorry Ohiofem for asking too many questions. I hope you don't mind that :)



    Bookmark   September 30, 2013 at 1:25AM
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Ohiofem(6a Ohio)

I would add 5 tablespoons of fertilizer to the tomato pot and 4 tablespoons to the pepper pot each time you feed. You can allow the composted manure to come close to the stem of the plant. I would only be concerned about the undiluted fertilizer getting within a couple inches of the stem. Watering with compost tea, maybe every couple weeks, sounds like a good idea. Try not to get the liquid on the plants, but don't worry about getting it close to the stem.

Pay attention to how your plants react. They should show growth in a week or two. If they suddenly wilt, you could be adding too much fertilizer.

    Bookmark   September 30, 2013 at 10:09AM
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