My gazanias have been left in over last winter and have grown larger this summer. Should I leave them again or can I cut them back?
You can leave them to die back or cut them back.
Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
I have a very large garden pot which is full of Gazanias from last year. Living in quite a mild climate, I left them in over winter. They have some green leaves, but mostly died off leaves looking like dead grass. I think they will be ok for this year. My question is, do I cut them back to virtually ground level to allow new growth?
You can cut the foliage back to 2 or 3 inches above the ground with pruning shears, which will encourage encourage new growth.
For more information on the care of gazanias, please visit the following link:
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
I bought a gazania last year and it bloomed for months. It has now filled the pot and there are lots of dry looking leaves from last year. It looks healthy but I wondered if I should remove them?
Yes, you can prune away the dead plant material.
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
I keep my plant in the house. It does have a bloom, but it do not open. It is in a plastic pot, must I replant it? Thank you.
Your Gazania likely needs more sunshine.
Try increasing the amount of sun that your plant receives.
Here is a link to refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
How can I encourage my gazanias to produce more flowers? They have great foliage, and propagate well. But not nearly as many flowers as they used to have. The gazanias are about 8-10 years old and used to flower a lot. But just a few flowers now.
Poor flowering on gazanias can be attributed to too much nitrogen (which promotes healthy foliage at the expense of flower production), not removing flowers as they start to fade (energy diverted into seeding rather than flowering), insufficient lighting, etc. However, given the age of your plant, I suspect the problem may be due to overcrowding. Gazanias have a tendency to become crowded after a few years. In this case you should dig up and divide into clumps to re-plant.
Gazanias---can you force flowering by day-light length? Thank You Phil
No, it would not be possible to force bloom these plants in an outdoor setting.
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
I've had my gazanias planted for about 3 weeks. The first week I watered every other day. Then I read they don't need that much water so now I water them about once every 5 days. Most of the flowers look dead, even when the sun is out. I'm in SoCal so it's hot. How much water and how often should I be watering them?
It appears that you need to water more. Daily watering and even twice daily if the temperatures are above 80 degrees F. Though they are considered a drought tolerant plant, that is only after they are well established.
Soil should be well draining.
It appears you have pepper plants in the bed also, and the yellowing leaves indicate a watering issue. In this case it appears you need to water your beds more.
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
https://www.gardeningknowhow.com/edible/vegetables/pepper/pepper-yellow-leaves.htm