So for this fall/winter/spring I am going to try a different approach. I wanted to see if anyone else has experience to share.

My observation is that the ants bring the aphids to the plants and nurture them. When they are lots of ants there are lots of aphids. When I can knock down the ant population (temporarily), the aphids don't seem to build up as much.

I grow greens in ground beds in the greenhouse floor, and I watch the ants busily traveling along the soil surface. I've noticed that plants in containers are less visited by the ants and have 90% fewer aphids. So I am switching to growing all my greens in containers instead of in the ground. I am hoping that growing the greens in containers will result in a cleaner crop, and I'm hoping that the ants don't immediately figure out that the greens are now located somewhere else and resume their aphid farming in the containers.

Does anyone else have an observation about this?
Are there other strategies for keeping the ants away? We dreamed up ideas like making a water-filled moat around the ground beds, or creating barriers of tanglefoot, both of which seem excessively complicated.

So I'm thinking I will try growing greens in large metal trays up on the greenhouse shelves. I found a huge selection of different types and sizes of trays from McMaster-Carr. What a great resource for greenhousers who are looking for random materials! My plan is to get metal trays with handles, 18" by 13" and 4" deep, and line them up on the greenhouse shelving. I'm thinking the trays will allow me to sew dense plantings of mesclun as well as individual plants of head lettuce. To me this seems easier than having many individual pots.

One thing I really like about having a greenhouse is the experimental nature of trying to figure out the best way to get the results you want. So this is my next step in that direction!

In my case it is not aphids but scale and mealybugs. My main ant control approach has been Tanglefoot, but most of my trouble is on dwarf fruit trees, where Tanglefoot is easier to apply. I use about 1" of masking tape and TF. Also I think is to get the plants in containers outside in the summer. Finally, there is is companion planting. Purely anecdotal, I have no studies to support this observation, but the section of the GH with all of the garlic chives just doesn't seem to have the pests I see elsewhere.

I looked at your metal tray. i think you could find something more cost effective that would work better for your plan. I think that thin metal will have a short life span, and needs drainage holes or things will drown. One suggestion is a company called Anderson that makes tree band pots for grafting,etc. They make a square tray 5 inches deep with good bottom drainage. It is injection molded plastic that should last for several seasons or more depending on the UV exposure. I have built a table with treated lumber and plywood and drapped in a rubber liner. I added a edge board around the border to make a very large 48"x32 foot tray. This entire surface could be filled with soil. i pitched it in one direction so the excess water will run off.

I have been growing in a greenhouse for about 14 years now. Those ants and aphids still give me problems during certain seasons. They seem to find ways around impediments. Some growers shut their house up tight in the middle of the summer for a few days and cook everthing so you can start fresh. During the spring when lady bugs are going strong, as well as aphids, I go around collecting there eggs layed on leaves outside the greenhouse, and bring them to the greenhouse crops to hatch. Once these hatch they will do a lot of damage to aphid populations. I have had some success with release of ladybugs, but they are generally not happy staying in a greenhouse and fly away soon. They will surpress aphids and if aphids are in high numbers lay there eggs in infested areas, before they start their migration. Unfortunatly with beneficials you are not able to soap if you expect them to do their job, so it is a difficult thing to figure out if you should stick with soaps sprays, or hope the beneficials take off. It will work well certain times of the year before the season gets too warm. I have also had natural populations of parasitic wasps build up, so keep an eye open to that as well. They can be purchased, but because they have to be overnighted shiped, they are too expensive. If you see leaves with mummified aphids remove it from your crop but keep it in the greenhouse. this will allow the wasps to hatch out and seek out new aphids.

Good Luck

Get some of those clothes dryer sheets like Bounce (get the cheapest stuff you can find), cut or tear them into 1/2 to 3/4" strips and staple the ends together to form lengths long enough to go around your containers. If your containers have rims, put the strips just under the rims and fasten with another staple, or tie in a knot.

The scent is also supposed to offend white flies and keep their numbers down, also.

Another way is using that brightly colored surveyor's tape and Tanglefoot. Tie a strip of the tape (the color doesn't matter, it's the width that is handy) and tie it flat around your container, then smear with Tanglefoot. Keep an eye on the strips -- if they get coated with dead ants, new ants will just walk over the dead bodies of their comrades. Just cut, remove and replace. Applying Tanglefoot directly to the surface of a container is just begging for more work! Keep it simple.

If you see where ants are coming in, coat a stiff piece of plastic (page protectors) with a thin coating of Tanglefoot and place it where they have to walk over it. DIE, ANTS, DIE!

Sue

That's helpful info, thanks. It's always nice to benefit from others who have much more experience. It sounds like you have a sweet setup!

I did go ahead with the metal trays and they turned out to be nicely sturdy. We plan to drill holes in them for drainage and I'm in the process of painting them a nice shade of light green. When full, they'll still be maneuverable because they've got handles.

As for the aphids, the other day I discovered aphids setting up camp in the lettuce that was planted in hanging baskets. Ants can't likely be blamed for that, so I guess the aphids will find their way to anything that is tasty for them.

However the aphid population on the plants in the ground is much, much greater than the few aphids I've come across in my container plantings so far. Lettuce and other greens are growing happily in the containers and I'm looking forward to getting the trays ready for planting.

We'll see what happens.

Dryer sheets and tanglefoot also sound like ideas worth looking into, thanks!