One of my hibiscus plants has yellow leaves, why?
The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
They turn yellow and fall off - am I over watering or underwatering?
This article should help pinpoint the reason for your yellowing leaves: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Is most certainly over watering. I have just bought a lovely apricot colour one and was told by the nursery that they don't like too much water as they are from New Zealand and that the leaves would turn yellow and droop if too much water. Hope this helps
Plant blooms well, but leaves turning yellow and falling off. Watered well but not too much.
There are several reasons this can happen, normally associated with stress of some kind. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Why are the leaves on my hibiscus plants turning yellow? The flowers are beautiful and plenty of them! Some of the leaves are falling off.
There are several reasons this can happen, normally associated with stress of some kind. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Mine turn yellow if I give the plant too much water. Just a little each day does the trick, like 3/4 of a cup.
The problem has now spread to the three adjacent plants we have in large pots, which have plenty of sunlight.
It sounds like they have galls. These can be unsightly, but are typically harmless to the plant. They can get unsightly though. Some galls are caused by a fungus and will spread, which sounds like what is happening here, so the leaves will need to be removed and destroyed (including any foliage on the soil around the plants). You can also treat them with neem oil to help control the problem.
The bug tends to creep on the underside of the leaves, creating holes in leaves. Today I noticed it was nested in a new bud waiting to open. What can I do to get rid of this bug?
It sounds like it may be thrips. This article will tell you more about them: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
We have been very pleased with our trials of using neem oil for killing these kinds of pests (and many others, should the pest in question be something different). It is safe for humans and pets, as well as beneficial bugs. You can learn more about it here: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Do you trim off spent hibiscus blooms?
While you can deadhead if desired, this practice is not necessary. Your hibiscus plant will be fine left as is. The spent blooms will drop on their own.