container orange defoliation

creekweb(6,7)January 25, 2014

I have 2 container orange plants about 12 years old growing in 12 gallon pots, the larger about 6x5 feet. They stay in a sunlit inside room during the cooler seasons and outside during the warmer. Two years ago, the pot of one of them developed drainage problems and the tree defoliated and ended up losing about 2/3 of the branches. My salvage efforts at the time included changing both trees to larger pots, enlarging and increasing the number of drainage holes and changing to a faster draining mix. Both trees steadily improved over the past 2 years, and the larger set a large number of blossoms which began opening earlier this month. Then about 4 days ago, the larger tree began to defoliate especially new upper leaves and unopened blossoms. It has since lost about 3/4 of its leaves. At first, I suspected inadequate watering and gave extra, but leaves continued to fall. I then pulled the tree up out of its pot to examine the roots and medium. The tree was not rootbound, There was no trapped water and the medium if anything looked dry and the roots looked dry and in poor condition. The other tree sits right beside and is unaffected. Over the years, I've neglected the watering of this tree on many occasions and it had never defoliated, so I'm hesitant to chalk this up to just inadequate watering. Might it be that during the blossom period orange trees are particularly sensitive to water requirements and much more prone to defoliation than at other times? Or am I missing something?

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tapla (mid-MI z5b-6a)

Your plant probably needs repotting, which includes root pruning and a change of soil. If the plant is 12 years old and has never been repotted (as opposed to potting up), the inner root mass is undoubtedly a significant problem that will continue to limit the plant until it's resolved. The improvement in growth you noticed after potting up is indicative of the plant recovering only a fraction of it's potential for growth and vitality. The compaction might be so severe in the inner root mass that water can't penetrate, no matter how much you apply. I've seen several old root masses where the soil was actually much harder than even the primary roots growing off the bole.


    Bookmark   January 26, 2014 at 1:54PM
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hairmetal4ever(Z7 MD)

Al - my concern about repotting is that, if you bare-root the plant, and it has a dense, fibrous root system, is the difficulty in properly "infilling" the new soil around the roots in the proper way, since the roots are so dense. Not matting them, or kinking them, or mashing them all together, etc...

    Bookmark   January 26, 2014 at 4:09PM
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calistoga_al ca 15 usda 9

My experience with pruning the roots is it stimulates new root growth and benefits the tree. Al

    Bookmark   January 27, 2014 at 10:05AM
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That sounds right. In the mean time I've increased the frequency and amount of watering so as to penetrate the root mass and have arrested the defoliation. Now is not the most opportune time to do major root work on the plant since it is inside and will make a big mess, but I'd do it if necessary. My thought was to temporize with frequent waterings and increase N to encourage regrowth of leaves so as not to decrease the size of the tree until I can remedy the underlying problem in the spring.

    Bookmark   January 27, 2014 at 2:33PM
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tapla (mid-MI z5b-6a)

If you have a 'dense, fibrous root system', you chop off the bottom, then cut wedges out of the remaining root system equal to about half of the roots. At the next repot, you again chop off the bottom and remove the roots you left after the first repotting - alternate wedges, if you will.

The term rejuvenation pruning comes from the fact that plant growth tends to retain its ontogenetic age. That means that the closer growth originates to the root/trunk transition, the more juvenile (and thus, the more vigorous) it will be. Rejuvenation pruning. Pruning roots makes them more vigorous, or more accurately, it returns them to a more vigorous phase.


    Bookmark   January 27, 2014 at 3:21PM
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