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Osmocote- any good?

motorman1motorman1 Posts: 42
in The potting shed
Hi Looking at reviews of osmocote and it's usually highly rated. I've used it for quite a few years and the results are not amazing for me though. The plants look ok but they certainly don't push on and the growth and flowering is limited. I guess it's good to not over fertilise as I put some potash on a rhododendron and I'm pretty sure that burned the roots and I now have a sick rhododendron. The osmocote seems to prevent this kind of result other than that I'm a bit underwhelmed.

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  • AnomanderAnomander Posts: 88

    I was of the understanding that Osmocote is a slow release fertilizer so I think the results are not meant to be a super boost so much as sustained (but good) plant development.

    I think it would require more knowledge of the soil type and growing conditions to be sure but if what you did with the rhododendron is an indicator, you may be growing things in the wrong conditions. Potash on a rhododendron is a bad idea as potash makes the soil highly alkaline and rhododendrons, azaleas, camellias, hydrangeas (etc.) love very acidic soil. So it may be less to do with the volume ("over" fertilization) as much as the type.

    Which plants are you using the Osmocote on and where are they located (sun/shade/free-draining/clay, etc.?

  • motorman1motorman1 Posts: 42
    I use it generally. The last 2 green one for my agave, palms and houseplants.

    I'm trying the gro sure this year on tubs of flowering annuals.

    It saves time of course but I feel as though I need to boost the growth with additional liquid fertiliser.

    I use these fertilisers on my flowering perennials and also shrubs and clematis. ????
  • motorman1motorman1 Posts: 42
    I use it generally. The last 2 green one for my agave, palms and houseplants.

    I'm trying the gro sure this year on tubs of flowering annuals.

    It saves time of course but I feel as though I need to boost the growth with additional liquid fertiliser.

    I use these fertilisers on my flowering perennials and also shrubs and clematis. image

    The soil in neutral clay with builders debris. :-\

    Plants for sun are in their sunny locations and camellias and rhododendrons and Peiris are in light shade. image



    Apologies about the above. Doh!
  • AnomanderAnomander Posts: 88

    I see. I would work on adding well-rotted manure mulch in late autumn and trying to improve the texture of the clay. Builders rubble may help if it is gravel but lumps of concrete or brick would only impact the clay more. I would try to incorporate more organic matter to loosen up and lighten up the clay. Light shade should be good for the rhododendrons but add an ericaceous fertilizer to the rhododendrons to make the soil more acidic, and this can come in the form of a slow release fertilizer (MiracleGrow does one). The potash will definitely have made them unhappy very quickly. The well-rotted manure forked in around them as a top dressing will also help to make the soil slightly more acidic. Otherwise, be patient, lay OFF the fertilizers a bit or only use them as light liquid feeds.

  • motorman1motorman1 Posts: 42
    Cheers for that. I've only limited scope for putting in a mulch as the garden has been previously landscaped with gravel etc and the fleece to keep the weeds out. I cut holes in the matting for my shrubs and perennials.

    I'll give the plants a few handfuls of well rotted compost for sure. ????????
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