We live on about 45 acres in Santa Barbara county, California; zone 23. Our house is on the East side of a ridge that separates us from the Pacific Ocean to the west, so we do not get a lot of sun at this time of year. We have young (1 - 2 years old) Hibiscus Rosa Sinesis in pots. They seemed robust until about 2 weeks ago, when we experienced an unusual cold snap, with temps dropping to the mid-thirties (F). I do not think that we actually hit freezing temps, but it was probably close. Two of the hibiscus have started to wilt. They are receiving water and are being properly fed. What is the diagnosis? What should we do; should we cut them back or are they goners? Please advise. Thanks.
What does "being properly fed" mean? Most of the time, plants don't need any fertilising at all, unless a soil test shows a particular deficiency. Maybe they are suffering from soil salinity caused by over-fertilisation.
Thank you for your note. We only feed with organic compost, every 4 months or so. They were thriving until the cold wave hit. This is a tropical variety of Hibiscus, so my concern is that they might be overly-sensitive to cold (?)
Hi Dicidupont, Just because the leaves were damaged by the cold temps doesn't mean the entire shrub didn't survive. Leaves are expendable to shrubs and trees when they're under stress and they will shed them. Wait and see if the shrubs sprout new leaves before doing anything. Newt
Thank you for your note. That sounds reasonable. The stems and branches are green inside; only the leaves seem to be having a problem right now. We'll hold off and see what happens. Thanks again.
If the stems and branches are green inside then they probably survived. Make sure there is a 2" to 3" layer of mulch to protect the roots and that it's not against the trunk. Happy New Year! Newt
This is a tropical plant, not much cold tolerance. Plants in pots more vulnerable to frost than those in the ground, too, as roots are much less hardy than tops. If your hibiscus are still alive they will re-sprout later. Then you will know. If they turn brown and shrivel, all the way down that can be taken as an indication they didn't make it. If you live in one of the canyons through which cold air drains from the interior out to the ocean you can expect additional temperature plunges in the future. I visited a bamboo enthuiast down there once who lived quite near the ocean, but in a canyon. He had had temperatures in the 20's (F) the night before. Tropicals can't take hard frost like that at all.
There are two possible scenerio: (1) The cold had damaged the root-hairs and the leaves are drying up due to water loss caused by transpiration and they do not receive water replacement (no osmosis). (2) The cold damaged the leaf cells causing them to burst their cell wall due to expansion when water freezes. If this be the case then just remove all leaves without pruning or with light pruning and come spring the buds will break without any set-back. If (1) is the problem then remove all leaves also to conserve any traces of water in the stems. You may save the day if the main and larger branch roots are intact and the plant has sufficient food reserves to grow new root hairs and new leaves come spring.
Looking at the photos, I believe the leaves are not totally dead (i.e dried up) but definately headed in that direction. Thus defoliating helps to conserve whatever reduced volume of water still existing in the stems. If the root hairs had been killed by frost then the plant's priority is to regrow these organs first to uptake water before any growth can commence above ground. If only the leaves are damaged, I would still defoliate as there is no possibility of taking advantage of leaf senescence at this stage.
With barerooted hardy stock no growth of new roots occurs before dormant stem buds have begun to open. In fact, the opening of the buds is what causes the new roots to appear. So, I have to wonder if these hibiscus will regrow part of their roots while the top does nothing. Continue to suspect taking the time to pick all the leaves off unnecessary at best. If dead they may soon drop on their own, anyway.
With barerooted stock, I believe the roothairs are intact as you need to keep the root system moist during storage or transport. When the buds open I believe there is a tremendous demand for water for leaf cell division or enlargement. I doubt the plant would have sufficient water stored within its cells to accomodate this growth, thus the need to depend on osmosis at the time of bud breaks. However the truth of this observation can be quickly tested by removing the root-hairs of barerooted stock you had referred to. I will be quite interested to know outcome if you do carry out the experiment.
Barerooted stock has no root hairs left, indeed few feeder roots. Hormones generated by opening buds at stem ends cause new roots to grow.
I would like to hear how your hibiscus turned out after your "cold scare". Sorry I saw this post only now. I am on the border of zone 8/9. Most years most of our hibiscus planted in the ground go dormant. If the root system does not freeze, we cut back dead branches and they sprout again in the spring. The last few days we had an overnight low of 30, the leaves on the potted ones drooped like the ones in your photo, I brought them in the house, and they sprang back up withena few hours. They are looking good now, we are in the 60's and 70's F. I bet yours are lush and full of blooms. I just wanted to post this for future reference. check out www.dupontnursery.com They hybridize here in Louisiana awesome!!!
