Measure the width of your test tube. Add an inch to your measurement to find the ideal width and depth of your pieces of wood. Choose a length that is no less than an inch, and no more than the height of your test tube. Cut your piece of wood according to these dimensions.
Draw out the shape of the opening of your test tube in the middle of the top of your wood piece. Adjust the marking if your test tube has a rim so that the circle is the same size as the body of your test tube.
Drill a hole using your power drill through the drawn out circle. Remove a smaller portion if you are unsure of the correct dimensions and insert your test tube in the hole to see if it fits. Keep enlarging the hole until the test tube fits snugly inside the wood piece and doesn't drop right through. Use sand paper to thin out the walls of your wood block when you get close to the perfect fit.
Choose one side as the back side of your hanging vase. Make a small indent on that side with your drill where the wall hanging hook will be. Hang your hook on the desired spot on your wall. Test it out to make sure the block of wood hangs as straight as possible.
Stain or varnish the wood piece to protect it. Let it dry completely before inserting the test tube into it. Use sand paper along the edges of the hole if you put on too much paint and it is now too small to fit the test tube.
Insert the test tube in the wood piece. Place your flower in your test tube. Fill it with water. Hang it on the wall.