What are different varieties of wall creepers of perennial nature suited for dry climate?
The links below have several suggestions and care information on many perennial vining plants.
I would also suggest you talk with your County Extension Office; they will have a list of specific plants to your growing zone.
Here is a link to help you locate your nearest office.
https://www.gardeningknowhow.com/extension-search/
https://www.gardeningknowhow.com/special/xeriscape/growing-drought-tolerant-vines.htm
https://www.gardeningknowhow.com/ornamental/vines/ovgen/covering-brick-walls-with-vines.htm
https://www.gardeningknowhow.com/garden-how-to/design/lideas/using-plants-on-walls.htm
https://www.gardeningknowhow.com/ornamental/vines/ovgen/growing-plant-cover-fence.htm
I live in zone 9 in southern California. Why does the hardiness map only cover cold temperatures and not hot? It gets up to 110 F here and a lot of plants designed for full sun just don't survive the summer. Are there flowers other than cactus and succulents that would work?
Yes, there are many perennials, vines and shrubs for you to grow in your warm zone 9 climate!
I would also suggest you check with your County Extension Office for a list of plants specific to your region.
I have listed a link to help you locate your nearest office and a few other links to help you.
https://www.gardeningknowhow.com/extension-search/
https://www.gardeningknowhow.com/special/xeriscape/growing-drought-tolerant-vines.htm
https://www.gardeningknowhow.com/ornamental/shrubs/plumbago/growing-plumbago-plants.htm
https://www.gardeningknowhow.com/ornamental/shrubs/princess-flower-bush/growing-princess-flower.htm
https://www.gardeningknowhow.com/ornamental/shrubs/ixora/growing-ixora-shrubs.htm
https://www.gardeningknowhow.com/ornamental/flowers/gazania/gazania-treasure-flowers.htm
https://www.gardeningknowhow.com/ornamental/flowers/angelonia/growing-angelonia-plants.htm
I have 2 large planters in my office that currently have zz plants and mother tongue. I wanted to add more to each planter to fill some of the lower growing space. The planters are each 4' long x 1' wide x 1.5' deep. Do you have any suggestions? One planter is positioned in front of a southern facing window and the other planter is not near direct light. Thank you!
Philodendron or Pothos would make a nice addition to your planters.
https://www.gardeningknowhow.com/houseplants/philodendron/caring-for-philodendrons.htm
https://www.gardeningknowhow.com/houseplants/pothos/pothos-plant-care.htm
What perennials can I grow that will provide color under sabal palms (zone 9)?
Copperleaf, Gardenia, Cape Jessamine, Aloes, Japanese holly fern, Christmas Fern and Dragon Wing begonias would be good companion plants.
Also check with your County Extension Service for any other suggestions for you region.
Here is a link to help you locate your nearest office.
I'm in Boston and our apt balcony has zero sunlight. Are there plants I can grow for privacy?
There are all kinds of plants that thrive in the shade!
This article gives a nice broad list sorted by type:
https://www.gardeningknowhow.com/special/shade/finding-a-shade-loving-plant.htm
Since you're planting on a balcony, this article about shade container plants should be helpful, too:
https://www.gardeningknowhow.com/special/shade/plants-for-creating-shade-containers.htm
What flowers can I plant in window boxes that will flower and fill it in the shade?
There are plenty of flowers that grow well in window boxes and the shade. Begonias, Impatiens, Pansies, and Snapdragons are all compact and shade-loving.
Here's a good list of flowering shade plants:
https://www.gardeningknowhow.com/special/shade/shade-tolerant-flowers.htm
And here's another good list of shade plants that do well in containers or boxes:
https://www.gardeningknowhow.com/special/shade/plants-for-creating-shade-containers.htm
I have a rocky, sunny backyard about 40 miles east of Austin, TX. What type of plants would be best and will use little water? Thank you.
There are plenty of plants that like sunny, rocky soil and need little water.
Xerophytes in particular are perfectly adapted for your conditions. Here's an article all about them:
https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/xerophyte-desert-plants.htm
Here's a broader article about good drought-tolerant plants:
https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-plants-for-nearly-any-landscape.htm
The best and easiest way to ensure your plants do well in your climate is to choose native species. Here's a great (if kind of dense) resource for plants native to your area:
http://water.tamu.edu/files/2014/01/central-texas-landscaping-plants-guide.pdf