I recently bought some tree fertilizer spikes to feed my potted dwarf kumquat and lime trees. After I got them home, I read the following warning on the side of the box:

NOTE: Never apply within 30" of the trunk.

Obviously, my pot's radius is less than 30 inches so I would need to go against the instructions if I were to use the spikes.

Is the 30 inch warning there to protect the tree's roots from being spiked (in which case I can be careful and take the risk) or because the fertilizer itself will damage the tree being in high concentration (in which case I should return the spikes)? Or is there some other reason for the warning?

Update: One suggestion below is to break the spike in half to reduce the concentration of fertilizer. Is that a good idea?

Final update: The die is cast and I've put half a spike in each pot. Depending on how the trees respond, I'll post any further updates as answers to the question.

2 Answers 2


I can only speak to how I feed my potted citrus. I typically use an amount of Osmocote Plus (orange bottle) extended release fertilizer. It's a slow-feeding ~6 month fertilizer that seems to work pretty well with my citrus (no burn). I use this along with a periodic application of Miracle Gro Miracid.

I believe you're right: fertilizer spikes could burn in that small of an environment. If you're interested in using them, then perhaps you could break them up and spread out the application of one over a few months.

I'm no expert but that's what I'd do.

  • How often do you feed your trees? One of the attractions of the spikes for me was that I figured I get my time commitment down to watering once a week, putting in a new spike twice a year, and harvesting more often. I've failed to feed my kumquat in the last two years and it's starting to show signs of starvation. Jun 9, 2011 at 17:59
  • I typically put some Osmocote on 2-3 times per year (like your fertilizer spikes). Then I just take a look at the leaves to see if they look healthy/green to me. If they look a little pale then I'll mix up some Miracid to green them up. I've also heard you can use a diluted Miracid/Miracle Gro mix every couple of weeks, so maybe every other watering in your case. You definitely have the right idea with pursuing low-care solution.
    – Tim Clymer
    Jun 19, 2011 at 1:47

Not necessarily

My trees are on their second spike each and both have plenty of good, green leaves and fruit. Breaking the spikes in half might have helped and will reduce my overall costs. I'd say this is a dead simple solution and I'm quite pleased to have landed on it.

(For reference, the spikes in question are Jobe's Organic Tree Fertilizer Spikes. I have no reason to assume these are better or worse than any other product. I just found them in a local hardware store.)

  • 1
    Those spikes are "organic", balanced & have low N-P-K numbers (5-5-5), therefore are nothing like some of the "crazy" chemical spikes certain companies try to push. I would be (very) surprised if the "organic" spikes you used caused any problems, especially when using half a spike at a time...
    – Mike Perry
    Oct 18, 2011 at 23:06
  • @Mike: Sounds like I might have gotten lucky then. ;-) Oct 18, 2011 at 23:07
  • Isn't that what gardening is all about "luck" ;-) It is for me...
    – Mike Perry
    Oct 18, 2011 at 23:11

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