hibiscus syriacus in container needs help

sagesproutOctober 19, 2011

I have two hibiscus in containers right now. One is a tropical hibiscus (rosa sinesis) that is doing wonderfully and being pruned into a small tree. The other one is a deciduous hibiscus syriacus called "alba" that is not doing so well in a pot. I got it last year when it was about 6 inches tall. It is about a foot tall now but unhealthy. It barely flowered at all, so I repotted it in a larger pot and then it stopped flowering and the leaves turned yellow around the ends in springtime, during flowering season. I am aware that the leaves are supposed to fall off in the autumn. I was wondering if hibiscus syriacus is difficult to grow in pots. Would it be better off to plant it in the ground?

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tapla (mid-MI z5b-6a)

Hbiscus makes roots at an amazing rate, so it's important to radically reduce the roots yearly and do a complete repot, usually accompanied by a hard top pruning. They also like a lot of fertilizer, but low doses of Phosphorous, so 3:1:2 ratio fertilizers + a little potash mixed into the soil, or regular applications of a liquid K (potassium) supplement work very well - "bloom booster" fertilizers do not. Like most plants, it will rebel at being over-watered, which is often a function of soil choice + watering habits. What were/are you using for fertilizer?

Al

    Bookmark   October 19, 2011 at 7:20PM
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sagesprout

For fertilizer, I was first using a granular time release bloom booster "colorburst" brand (15-30-15). Then I tried giving it Bayer 3-in-1 that has fungicide and insecticide in it.
Do you think it would be okay to change the soil right now and add perlite? Or should i wait till it goes dormant in the winter? I'm afraid since it's so weak looking that anything I do might make it go into shock.

    Bookmark   October 20, 2011 at 12:08PM
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tapla (mid-MI z5b-6a)

I would saw the bottom 1/3 of the roots off now, and make some deep vertical cuts in the root mass & pot up 1 pot size into a soil similar to what it's in now. As the plant is waking in spring, I would saw 2/3 of the roots off, bare root, pot into a free draining and durable soil, and prune the top back hard.

Skip the bloom booster fertilizer for these plants - they do not like it at all. When you said Bayer 3-in-1, it sounded almost as though you replaced the 15-30-15 fertilizer with that product, but their 3-in-1 doesn't include fertilizer. It has a systemic insecticide, a systemic fungicide, and a miticide. Their ALL-in-1 product contains fertilizer. Did you get them confused?

Al

    Bookmark   October 20, 2011 at 8:46PM
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sagesprout

Okay, so it sounds like I will have to stop giving it bloom boost fertilizer. I've never heard of making vertical cuts into the roots. Could you explain to me the reason for that? Thanks, Al.

    Bookmark   October 27, 2011 at 12:07PM
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tapla (mid-MI z5b-6a)

Cutting the bottom of the root mass off and filling the new and larger pot with fresh soil at the bottom will create soil volume for fine roots to colonize & absorb nutrients/water. Also, you undoubtedly have roots encircling the outside of the container that are/or eventually will be choking off the other roots and growing back toward the center of the root mass. Truncating the encircling roots via the vertical cuts stimulates branching of fine roots behind the cuts. the fine roots can then also grow out into the fresh soil surrounding the old root mass where they can absorb water and nutrients more efficiently.

This is a temporary measure that will allow your plant(s) a measure of increased vitality while you wait for a more appropriate time to prune roots properly. It's much better to have a plant with good energy reserves at that time than a plant that's fraught with serious root issues and circling the drain.

Al

    Bookmark   October 27, 2011 at 2:44PM
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