Liberally sprinkling black pepper around all of your plants normally works well. Cats are particular about where they go and sniff around to find just the right spot. A nose full of pepper is a pretty good deterrent for most cats. I buy the super size cans at places like Big Lots, Sams or some other discount store.
A sprinkle of cayenne pepper (or any ground, hot pepper or pepper flakes) also works well. I've had great success over the years using ground red pepper anytime I have a problem with dogs using my lawn for similar purposes. I've watched the offender sniff the lawn and then leave pronto w/o depositing anything. Nips it in the but pronto, and they don't return. Seems like they don't want to risk getting pepper on any sensitive parts. My guess is it will be equally effective with cats. (Red pepper is probably more expensive than black, but it is possible to get it in large containers at a pretty low price either in the Spanish section of grocery stores or sometimes at dollar stores.
Another option would be to lay some kind of light fencing material (chicken fence or the type with narrow rectangles) on the ground in areas you need to protect. Use something thin/flimsy enough to work with easily. Cut to fit and lay flat on ground in aisles, on beds, around plants, etc. They won't be able to dig with the wire in the way. It will irritate their paws and they will go elsewhere. If you have some spare bricks or rocks, you might want to use one here and there to anchor the wire.
There is also a product you can buy that works on the same principle as the wire but which is made specifically for this purpose. It has rubber or plastic 'spikes' that stick up. They don't harm the cat but make it difficult to dig in the area. Depending on the size area you are trying to protect, it may get expensive though. Most of the big, online garden supply sites probably have it along with places like Amazon. I've seen it at Gardeners Supply, a site I've used many times with excellent results and which has an excellent rating in Garden Watchdog (or did last time I checked).
Blake, your problem should be easily remedied. There are lots of cats out there in need of good homes. I adopted 2 strays myself recently. It's not that we don't love cats. It's just that we sometimes need to dissuade them from adopting our gardens as litter boxes.
If you really want to attract cats (and assuming there are some loose in your area), you don't really need to plant anything, just till some land. In all probability, the cats are not interested in snowboi's plants but rather the soft, freshly turned earth which makes the perfect litter 'box'.
In many areas, it's very difficult for outdoor cats to find a place where they can dig easily to do their 'business'. Where I live, for instance, every square inch of soil is covered with something: houses, streets, sidewalks, lawns, forest, etc, none of which makes for good, easy, digging. Gardens, on the other hand, are perfect. (Thus, the 2 strays I adopted dig in my flower beds and large flower pots when they are outside.)
I normally use black pinebark mulch in all of my beds. One bed I had completed...the store was out of my mulch. I grabbed a couple bags of cypress mulch to finish my job. The cats NEVER EVER try to use that bed. I hate the drab color of the mulch and I will admit that it is pokey and you have to wear gloves to dig around. But the cats hate it.
For the other beds--when I trim my rose canes, I select the most prickly ones and lay them in the areas the cats are using. Also any spare rocks can be used between plants. This is not all that attractive, but it works most of the time.
Added: I just now followed the link about the plectanthrus. Several years ago I planted a variegated plectanthrus which had a trailing form in my beds. That was the prettiest and easiest groundcover. I have looked for it ever since but have not found it. I wanted to say it was also called Swedish Ivy.
I have a cat that does the same in any newly dug soil, it apears to be there nature yeh right !!!!, what I do is stick some garden canes or pea sticks into the beds at a couple of feet apart, so i'm like making a mini fence posts, then I use a reel of cotton thread and criss cross it back and forwards and up and down all around the canes, the cat dont like the thought of being trapped in the cotton thread as they cand see a way out.
If you have to chase birds etc away, you can tie either strips of tin /baking foil at intervals so it moves in the breeze, or cut strips from a plastic bag and tie thos in the same fashion, the plastic dont get wet from watering or it does but it is not harmed.
Maybe this will give you some relief. good luck. WeeNel.
My cat was a garden pooper, too! He even dug through bark mulch to do his "business". My solution was to put a litter box on the backyard patio. While it is not attractive to have a litter box in the garden, it keeps him from digging around. And, it is easy to slip it into the laundry room when company comes over. Another bonus was less smell in the house! MrCs Mom.
Now that you mentioned this, I have a very large, shallow pot in my backyard garden. It's about 2.5ft wide and 6-8in tall. It used to contain herbs, but they died somewhere along the way, leaving only the large pot of loose soil. One day when I was out in the garden, I noticed one of my cats hop in the pot and do his thing. Since then I've seen both cats use the pot several times.
The upside of the pot of dirt is that it looks very normal in the garden, like flowers that haven't come up yet. Maybe you could try a hybrid of these two approaches: a short, wide flower pot with litter, perhaps adding a bit of soil on top after they get accustomed to using it, for instance, or a litter box full of potting soil.
How do you keep the litter from getting wet in a rain shower? Clumping litter would seem to turn into a giant 'rock' after a rain. Oh, I see. You are from CA, where I'm guessing you don't get rain often.
After reading your post I was thinking I might add an outside litter box for my cats, in addition to the flower pot they currently use. Unfortunately, we get rain frequently here, and I don't have a place to put it where it would be protected by a roof. We have frequent afternoon showers and thunder showers, so that wouldn't be an option for me. I'll have to stick with dirt. (The flower pot they use has a hole in the bottom to let rain water drain through.)
I had forgotten about this until I read Domehomedee's post, but a few years ago my own cats were laying around in my iris beds. They didn't appear to be using it for a litter box so much as just wallowing around in the cool, damp earth between irises to keep cool in the summer heat. Unfortunately, in so doing, they were also rolling over the young iris plants and breaking them off at ground level. To discourage this behavior, I got some rose prunings, just 12in or so pieces trimmed from rose bushes and lay them on the ground between the irises. My thinking was that the thorns would cause the cats to look elsewhere for a place to sleep and play. It actually did work.