I bought a China girl holly bush in April. It was loaded with green berries. After about two weeks, all the berries disappeared. Why? Does this mean this bush will not have red berries in the fall? I have purchased now 4 weeks after the female a male China boy. Is it to late for the male to pollinate the female?
The female likely dropped the berries due to a lack of pollination. No pollination means no seeds and the plant will abort the berries. It may also have dropped the berries due to transplant shock - if it had been pollinated before you bought it. The male is too late for this year, but come next year, the female will produce new flowers/berries and has a male to pollinate it so you will get red berries in the future.
China Girl Holly has black coating on inside branches and leaves. How do I get rid of these? After this awful winter I have noticed that the holly has a black coating covering wood and leaves but only inside the bush. The outer leaves and wood looks OK?
This sounds like sooty mold.
Neem Oil is a good treatment.
Here is a link with more information.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
I bought China girl plant 2 weeks ago and it is on our balcony. It got very warm the past couple of weeks, up to 32 degrees C. I was watering the plant when I saw the soil was dry and moved it to shaded area at the balcony. I was worried the direct hot sun wasn't good for it. Now the leaves are turning brown and falling off. I have put new earth and in a larger pot. But it's like it got worse. I don't know what I'm doing wrong and worried it will soon die.
Generally a bright but indirect light indoors is appropriate for your China Girl plant. Soil should be kept evenly moist.
A shady location outdoors would be more appropriate.
Your plant suffered from the change in outdoor lighting and the roots drying out.
Keep the plant in a sheltered location and water daily or even twice a day in warm temperatures.
You will need to trim away any plant material that has died off, and wait and see how the plant recovers.
Will a China Girl Holly bear berries in the presence a Blue Prince Holly?
They SHOULD be compatible, but this is no guarantee. The only way to be absolutely sure of pollination is to have the same variety, but these are close enough in relation that it should be completely possible to cross pollinate.