I bought long, galvanized bolts with the same threading as the inside of the doorknob, and screwed them in. These were $1 each.
The doorknob-bolt combo fit down inside a 3/4″ galvanized pipe, which my husband cut for me, to 15″ each. The pipe we had on hand, but if you were to buy it, it is about $15 for a 60″ one, which yields 4 pieces. I wanted them long enough to pound into the ground far enough that the mower won’t push them out of plumb. I plan to leave the pipes in the ground year-round, and take the doorknob-bolt combo in for winter and set them back out in the spring.
I pounded the pipes into the dirt with my husband’s heavy brass mallet, so it did all the work for me, and didn’t smash the top of the pipe in. This was very easy, six or seven hits for each pipe. 15 minutes total for ten hose guards.
Drop the doorknob-bolt in and stand back and admire. (Now I can drag my hoses out of the basement and start the real work. Hahaha!!) My cost was $5 each, or $50 for ten cute hose guards. If you had to buy your pipe, they would come out to about $9 each. These seem a little pricy, but this is actually about the same as the more expensive metal hardware store ones which rusted through their weakest place in just one summer. But these are mostly galvanized, so I have high hopes that they will last a long time if I take the doorknob part inside in the winter.