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figuringitout

Understanding NPK fertilizers

6 years ago

Hi all, (I'm in Mass zone-5b)


I understand what the NPK stand for and their use by plants, but I'm wondering if there are default values for these when shopping for them. i.e. I see diff values for them for diff purposes (5,10,5 or 10,10,10 or 0,0,60 or 0,20,0).

I understand what they are providing, but is there a scale or list that the amounts run on or are there default amounts that you can get and where to look for them.


Here's why I'm asking.

I'm looking to be more specific with my fertilizing now and don't always want to be using a MG low balanced fertilizer, like a 5,5,5.

In particular, I'd like to start being better at feeding my heavy feeders, like pumpkin, squash, eggplant, melon, cucumbers, etc. at their different stages of growth.


I understand to have a bit more nitrogen on initial growth of plant,

then switch to more (P) value once flowers start developing,

then switch to more (K) value once the fruit start developing.


Generally, I would just use a default 5,10,5 MG type fertilizer, but I'd like to see if I'd get any better results by trying to go to the next levels to help the harvest.


Is there a book or web site that better explains the different values you can have and what product specifically to use to get them. Or what product should I be looking towards to target their diff growth stages. I'm up in the air with this at this point.


Thanks in advance,

Comments (8)

  • 6 years ago

    You posted to some forums that are no longer very active. After Houzz bought gardenweb forum participation really plummeted on some forums. I'd highly highly recommend reposting this on the Perennials forum, which is very active with some advanced gardeners, many of whom grow vegetables.

  • 6 years ago

    One approach you could take is to make your own customized mixes: bone meal is a traditional high phosporous fertilizer; you can also buy potash fertilizer — which is basically water soluble potassum salts. Mix these into your compost, potting soil, or a high nitrogen fertilizer like composted manure, changing the ratio as desired.

  • 6 years ago

    Hi all and thanks for the reply.

    Yes, my current soils are all fresh and new. The beds are new this year with loam, compost and basic fertilizer. I actually didn't realize to add in anything else particular for what I'm growing. I think I probably don't need to and will just keep an eye on things as they are growing.


    My heavy feeders this year, I guess, would be Tomatoes, Squash (Zuchini & Butternut), Pumpkin, Eggplant, Cucumbers and Melon).


    deanna, thanks for all your input as well. All good to know. I'll be looking into some of those ideas for this fall as well.


    nekobus, thanks for the info on mixing your own blends. That sounds like a good approach as well.


    I'm just trying to get a better understanding on the whole fertilizer story overall.

    With learning about the diff types, bonemeal, bloodmeal, fish/seaweed variations, worm castings, Texas green sand and rock dust just to name a few. Ugh! I'm just trying to see how they all work and when/what situations you might use them.


    I'm just getting my notes on all this stuff squared away for easy reference.


    Ok, off to battle my Tomato leaf curl problem I seem to have with two varieties.


  • 6 years ago
    last modified: 6 years ago

    My approach is to feed the soil microherd and let them break down the organic matter to release nutrients that feed the plants. This has worked well for me in good Ohio clay, in typical acid rocky NH soils, and in my current acid sandy soil. I am not aiming to grow prizewinning veggies, just food for myself and friends, so I add composted manure and compost, an occasional green manure crop like winter rye or buckwheat, and wood ashes to raise the pH a bit, and my veggies produce fine. My larger concern is adding too many nutrients to my local river and groundwater, so any added nutrients are slow release.

    Looks like your list includes the type of materials that will need to break down over time and microbial action. Are you growing in pots, or in beds that have some native soil? I do add water soluble fertilizers to pots since they don’t have the needed microbes for breaking down organic and some inorganic materials. Be aware that adding too much nitrogen for something like peppers will get you lots of green foliage with little in the way of fruit. And either P or K (I am too tired to look it up) can build up in some soils to create issues. So I usually suggest that folks do a soil test to find out what their soil needs to grow what they want. You want to remember that companies that sell various type of fertilizers are in the business of selling as opposed to doing what is best for your garden. Because different soils have different compositions, there isn’t a one size fits all set of recommendations.

    I don’t have any particular websites to suggest as I have been gardening since before the web was around, but would look at NOFA, and botanical gardens, and university websites for this part of the country to see what information they have available.

  • 6 years ago

    PS Both the veggie forum and the New England forum get regular traffic IME, but I haven’t ever visited the Master Gardeners forum, so I don’t know about that one.

  • 6 years ago

    Hi, Thanks for the input.

    I'll keep at it.

    I would like to figure out the best route for an inexpensive soil test.

    I suppose for the cost of having it done prof though, I'll just wait and see how plants do.


    Yes, I have a mix of containers and raised beds this year.

    Soil was all fresh loam and compost. I added basic fert when planting.

    All plants doing great so far.

    carrots,beans, peas, diff types of lettuce, cucumbers, butternut squash, zuchini, melon

    tomatoes, eggplant, potatos and some basil.

    Minor issues w/insects accordingly.

    I am going mostly organic on the protection though.

    Keep on gardening!

  • 6 years ago

    IME you can go rapidly insane trying to formulate special "feeds" for particular plants. My 60 years of gardening has been simply using triple 10 or 12 with compost, mulch, cow manure, etc. when available. Not trying to win any prizes, just grow reasonable veggies and have been very satisfied with the results. I'm also a firm believer in returning to the soil what you didn't harvest. e.g. after you've picked beans, run over with a rotary mower then till or dig back into the soil. Also like sheet composting I think it's called. Instead of a compost heap and turning and nurturing, just put whatever you have between the rows and ultimately till in. Weed control and makes earthworms very happy.


    Good luck

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