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I tried my hand at making my own soil for my citrus tree re potting. See below for the long story reasoning. I mixed EKO store bought (I live in an apartment) organic compost with coco coir and perlite. Its about equal parts of each, maybe a little less perlite. I tested the coir and it had a very neutral pH almost exactly 7 before mixing. After mixing and potting I watered and tested again, the pH was 6.5. Then the next morning I re-tested it again and this time the meter was around 5.4-5.8. It kept bouncing around allot. I am thinking that something in the soil parts must have taken time to dissolve into the water, hence why the measurement changed over night. Do I need to adjust the pH up a bit? Is this going to continue to change over the first few days? Assuming I am going to get something to be prepared to change the pH, if needed, what should I get? By the way its a 1 year old miniature naval orange tree and I live in Colorado if that matters.

Reasons for re-potting:

After 2 bad batches of store bought potting soil. First one did not drain well, second one (miracle grow) drained well at first and then I guess it broke down and did not drain so well. Literally I would water and 1 week later, in full sun, it would still be mucky an inch below the soil surface. Yes the pot has holes and I removed the drip pan because its located outside so who cares if the water runs off. This mg soil must have also had fungus gnat larva in it because it almost immediately got a bad infestation of them, with the little worms just under the surface. Hence I re-potted it in a pot that is full of many large holes, the kind with holes in the edge. Like what plants come in when you buy at the nursery. I then put that pot into a slightly larger pot.

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Was the compost you used MiracleGro Moisture Control potting mix? See gardening.stackexchange.com/questions/1402/… –  Mancuniensis Aug 31 '11 at 15:50
    
@startoftext, to go along with "bstpierre" answer, I recommend you read this, Sustainable alternatives to peat for potting compost, especially take note of, "If the label of the "brick" shows excessive salt content, the coir should be washed "thoroughly" before use." –  Mike Perry Aug 31 '11 at 16:40
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1 Answer

Citrus trees want about 6.0-7.0 pH. You can raise the pH of the potting medium with (pulverized) lime, but it's best to mix in the lime thoroughly when making the potting mix. I'm not sure that top dressing your pot with lime will help the pH much, though it may correct it gradually over time.

When making a soil mix, take into account the natural pH of the ingredients. Coir, for example, has a natural pH of about 5-6. (Peat moss can be 3.5-7 depending on the type you get, but it is typically quite acidic.) If the plant you're potting wants neutral-to-slightly-acidic soil (e.g. citrus), you should add lime to the mix. It doesn't take much, I use about a cup when mixing about a bushel of peat-based seed starting soil for vegetables. This amount is based on various recipes I've seen published. (The plants grow well, but I haven't pH tested the resulting mix.)

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What do you recommend for testing the ph? I have this:amazon.com/Luster-Leaf-1845-Rapitest-Digital/dp/B0032WFD5K/… but the readings seem to fluctuate greatly. For example I tested it at lunch today and at first it said 8 and 9 a couple times then it started saying 5.5-6.5 pretty consistently. –  startoftext Aug 31 '11 at 19:32
    
@start: I have no experience with the digital meters. I have an analog pH meter that's a piece of junk, as far as I can tell -- the readings bounce all over the place and are way off from what the lab results said the soil pH was. I've seen recommendations for pH testing using the paper strips you can get from pool supply shops but I haven't tried this. This would make a good question to post separately -- don't ask for specific brands or places to buy, but maybe ask which types of testers work best. –  bstpierre Sep 1 '11 at 3:15
    
point taken, I should probably ask that as its own question. Thanks –  startoftext Sep 1 '11 at 19:12
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