I grew it this year for the first time. It's beautiful! I bought plants from Walmart last year in bags, labeled "Blue Hollyhocks". I was so eager to see a blue one, but I was pleasantly surprised with two Nigras and one Watchman, which has a little more frill in the center. Sometimes, I suppose, Walmart's misnamed plants are a blessing. Jung seeds has the Watchman on sale for 95 cents: Here is a link that might be useful: Watchman Seeds

Air stones are horrible sources for infection. Do you really want to pump dirty air in your water? I grew dwc for 5 years and they were the only cause of trouble. You don't need them. Use 2 pumps, one to move water from the res to the buckets and the other in the res just churning the water like a lake with waves.

Ugh, I've seen a few on my roses already, and it seems early. Sadly, theres not much you can do. My father taught me to make a soapy bucket of water and pick them off in the early evening and drown them. They become sluggish late in the day, and are easy to pick off. Over the years this conversation has come up on this site and I've yet to hear anything that works to deter them.

How big is your property, and how close are your neighbors' lawns/garden? Milky spore will only help so much if they can just grow in your neighbors' lawns a few feet away and hop the property line. Same with traps: they will attract JBs from a long distance away and you may end up with MORE in your garden. But if your property is big enough--or if many of your neighbors also use traps/milky spore--then this might make a dent in the local JB population. I'm talking about putting out multiple traps over a large area (and preferably away from your garden) since killing a thousand with a trap will not make much difference if a million of them are living within a couple of miles and are attracted. In the end I resort to manual control: picking them off and shaking them into soapy water. It's just part of my normal garden routine along with pulling weeds, deadheading/pruning, and getting those danged lily beetles as well. I pick some off in the morning when I let my dog into the backyard, and then again in the evening after work and a trip to the dog park. These times are when they are most inactive and easiest to catch anyway. For the smarter ones that burrow deep into the petals to evade capture I use a pair of needlenose pliers to pick them out and minimize damage to the flowers.