Q:

How do I keep "cat grass" alive?

Sometimes I buy a little carton of grass at the pet store for my (indoor) cat to nibble on.  She likes it but it always seems to die off within a week or two.  I'd really love to have a sustainable grass colony if this is possible.  What can I do to maximize the grass's chances of surviving?

This carton only cost 99¢, but still...

A:

I went to Tractor Supply, a farm store, I'm sure there are others, and bought a 50 Lb bag of oat seed (hull on) for about $14.00. Horses like it.
I put a 3/4 cup of seeds in wet dirt in a 12" clay or plastic pot drip tray catcher with some holes drilled in it for drainage. Cover the holes w windowscreen to minimize dirt leakage. Dirt's about 1.5 inches deep. The cat loves it. Once sprouted, after about a week, it'll last 2-3 weeks before becoming rootbound and drying back. There is no stopping that, you're growing a big grass in a small space. Well watered, but not too soggy, keeps the stuff going the longest. Full sun at least part of the day helps grow thicker, juicier stems that my cat at least likes better. I keep two going at all times.
Edited upon further experience:  Regular fertilization with a weak fertilizer, I use Schulz African violet fertilizer because I have it handy, keeps the stuff green longer, as does 'mowing' with a pair of scissors when it gets over 6-8 inches (20cm) tall.

A:

The grasses chance of long-term survival were nixed at the moment when the seed were planted in the pot. 
Compare your pot of wheat, oat or other grains1 to a grain field: The individual plants need a lot more space to grow to their full height. The grains for cat grass are planted very close to each other (intentional overcrowding), allowing them to grow only for a short while befor the natural process of elimination leads to their death. This is intentional because a) that's the only way to get a nice "full" pot instead of a few meager stalks and b) because the customer has to come back and buy a new pot occasionally. Without assuming "unethical" motives, the growers know that most cats prefer soft (=young) leaves over old, tough ones and usually just nibble off the ends.
If you want to grow your own grass, you can plant the grains somewhat sparser than in commercial pots (but not too sparsely) in well-draining potting soil. A rather shallow container (2-4 in / 5-10 cm) will do as the roots won't go too deep. Let grow in a light place, possibly even outdoors until the desired lenght is reached. Do not make the pot available to your cat before the plants have grown to 2 inces at least because the roots should intertwine or your cat may pull the plants out of the pot, making a major mess... Ask me, how I know.
When the blades have been nibbeled on and the pot starts to look well-chewed, you can put it back outside and "mow the lawn", meaning you can cut back the grass to about 1-1/2 inch and let it grow back. If you are really lucky, you may repeat this a second time. 
By rotating two or three pots in various stages of growth and re-gowth it should be easy to have some available for your cat at all times. 
I personally choose not to fertilize my cat grass because I don't want my cat to eat any residue, even if it's organic and because I know that I will be "using" the pot only for a limited time.

1 I'm explicitly talking about grain-based "cat grass" only because I have read reports of some kinds of Cyperus (also sold as cat grass) causing cuts and other injuries. Better safe than sorry, IMHO.

