If you have clay soil you need to dig large holes for a plant and that hole needs to be ammended to make it friable I usually do a hole at least 3-4 xs larger than the pot the plant came in and replace 1/2 the clay with peat moss ,sand and steer manure mixed well . Tjis gives the roots achance to grow and also helps break down the clay. I use a good old fashioned fork for digging since the hole has to be big. If this is anew bed and you have the time a way to break up clay is to plant potatoes leave them in the soil and next year dig them in .

Sadly the above advice is out of date and incorrect.

Read Myth 2 at this link. https://ucanr.edu/sites/Tuolumne_County_Master_Gardeners/files/169971.pdf

Then Google ’bath tub effect in soil’.

It is also a myth that potatoes break up soil. It is the hard work of the gardener cultivating the potatoes which does the breaking up. And you certainly wouldn't dig in a crop of potatoes. A waste of a crop and a guarantee of spuds reappearing in future.

p.s. I’d forget the drill. Just get a good garden fork.

I move my potatoes around so all the soil gets a good forking.

If the clay is bad enough, does one use a spud to plant them?

tj

Outline your garden, put a good foot of compost, leaves to be composted or straw. Let it sit for a year or two. Your soil will be better.