I'm trying to build a raised-bed garden and have already run 1/2" poly tubing to each bed. I'm also trying to use the soaker hose I already had on hand as much as possible. The soaker hose is 3/8", and I need to connect it to the poly tubing. The place where I bought the tubing sells adapters like these:

, but they were apparently meant for poly tubing, not soaker hoses with their thicker walls, which don't fit. The soaker hose, meanwhile, came with fittings such as these:

How do I go about connecting the two kinds of tubing? Is such a thing even done, and if so, is there an adapter for this, or what's the easiest way to do it? Thanks for any advice on this.

My guess is that the "1/2" poly tubing" is the same tubing used in low flow garden watering systems. I connect my PVC watering system to both a low flow 1/2" system and a soaker hose like your pic. To connect to a 1/2" low flow tubing, use a fitting with one barbed end for 1/2" tubing and the other end a 1/2" female threaded connector. Then connect a 1/2" male threaded end and a 1/2" slip end connector; connect a 1/2" PVC pipe; finally connect a 1/2" inch slip end and a 3/4" threaded male connector. The soaker hose screws into the 3/4" threaded fitting. All parts are available at most hardware/ACE/Lowes/Home Depot.

I just discovered that my 3/8" (?) soaker hose fits almost perfectly snugly inside my 1/2" poly tube, so maybe the solution lies somewhere that way. I wonder, though, how to ensure that all of the water finds its way into the soaker hose, and doesn't leak.

You might try using a hose clamp to secure the connection.

Old thread...new Tik Tock video solution. Heat up the end of a threaded hose or whatever with a touch (be careful!) Twist in place the PVC over/inside the end to meet against the metal and create threaded ends