You branch off from the copper tubing with a 1/4" compression tee. Cut out a small section of tubing for which the tee replaces. You must use a tubing cutter to do this, any other method will cause the tube to become oval.
Install the short piece removed on the side outlet of the tee. Attach a 1/4" compression x 1/2" pipe thread adapter to the short section. If you can find a tee with a pipe thread side outlet (preferred), skip the previous step.
Connect a 1/2" pipe thread to hose adapter. When buying parts, ensure the male and female parts mate correctly. If you can't find the proper mates, get a short nipple or coupler to change gender. Use several layers of teflon tape on male pipe threads, wrapped in the direction that causes it to get more snug when the pipe is screwed in.
Attach hose and controller. After all this, there probably isn't much pressure left, meaning you could probably transition from hose to 1/4" drip fittings for the run from controller to plants, keeping the installation less obtrusive. If you use pressure adaptive drip fittings, you can better regulate the flow to each plant, otherwise the first plant will get the most water, the last hardly any.
Be careful, though unlikely in this case, as high pressure can cause drip fittings to blow apart. You also can't use most pressure reducers, as they can spill water as they function. You'll probably have to go from hose to 1/2" drip main to 1/4" drip distrubution. The 1/2 to 1/4 punched connection can leak slightly, so it should be done over the first plant.
When drip irrigation connectors leak, it is usually because the hole that was punched into the 1/2" hose is too large. This can happen when you try to re-punch the hole because the 1st punch did not go all the through and you can't get your connector into the line. When you try to re-punch a hole it's extremely hard to get the punch in exactly the same spot. Since you are off a tiny bit you actually end up with 2 holes, the one you put the connector into and right next to it a tiny hole that sprays out extra water. I've tried plugging the hole with the large end of the drip irrigation plug and sometimes that will stop the leak. When it does, then I just punch a new hole and try again. When it doesn't, then I use a silicone based glue to put around my connector. I get the type of glue that is good for fish tanks; I figure if it won't kill my fish then it won't contaminate my food.
Best Answer
I have something like this and it works just fine. (I have only one soaker hose in each bed, and both soakers are the same size.)
The flow rate involved is very slow, so the hose and connector sizes cause no interference. The pressure will be the same throughout.