The heucheras I've grown (mainly the new Heuchera villosa hybrids because they are heat tolerant) prefer soil a little on the dry side, but with regular irrigation. If you have clay soil, I would definitely use something like Permatill or even pea gravel and also mix in some organic material, such as compost.

Lime isn't necessary, mine all grow in acid clay amended with compost. Adding gravel for drainage can't hurt.

If you have clay soil, I wouldn't use sand. It'll make matters worse.
Compost or perlite (even better is Vermiculite)! Perlite is great for drainage, but vermiculite is not only good for drainage, but allows plants to take up nutrients better, unlike the perlite. Here's a great article on soil conditioners and fertilizers and talks about the perlite vs vermiculite:

Here is a link that might be useful: MCE Home and Garden

Thanks for the fertilizer link - saved a copy for easy reference :0)

Lot of errors in that link!! Much of the fertilizer information is OK but don't take it all as the gospel: current accepted horticultural principals do not advocate or recognize the benefit of gypsum as a soil condiitoner for anything other than sodic soils, most potting soils are soil-less mixes (do not contain any topsoil) and perlite, pumice or calcined/high-fired clay are far to superior to vermiculite as an additive to potting soils to improve drainage. And none of them are a reasonable addition to garden soil to loosen heavy, clay or poorly draining soils.....like, sand you need to add them in too great a quantity and at considerable expense for them to be effective. I don't even recommend vermiculite much for a potting/container soil. While it does improve drainage initially, once it becomes fully saturated with water, it collapses and any drainage advantage or porosity is lost......irretrievably.

You are far better off adding organic matter - compost - to improve and lighten clay soils. It is cheap (often free), it is a source of nutrients and trace elements itself, it encourages the activity of soil organisms that in turn do their part to lighten the soil and create nutrient availability and it retains moisture while still allowing for good drainage. And compost tends to mitigate swings to the extreme in either range of soil pH - it neutralizes alkaline soils and sweetens excessively acidic soils. Niether perlite, pumice OR vermiculite can make those claims or achieve those results.

It is important to remember that growing plants in the ground in a garden setting is vastly different from growing plants in containers or pots and the correct amendments (or fertilizing choices/frequency) for either are not interchangeable.

Heucheras grow best in an organically rich soil that is both freely draining and yet moisture retentive. And like most plants they will tolerate a range of soil pH but again, like the vast majority, will prefer a pH that is slight acidic (6.1-6.5) to neutral (6.5-7.0).

I have had a very interesting year with heucheras this year. I had several in a (all day) shade bed for two or three years that were declining, despite excellent drainage, consistent moisture, and good fertility. Last fall I moved them into a new bed where they get some morning sun but full afternoon shade. I amended this very heavy clay soil with horse manure and mulched it with chopped leaves last fall. In the spring, I gave them a very light sprinkle of cottonseed meal and mulched them anew with pinestraw. They have all thrived and actually increased in size this year. I don't claim that this is the full answer, but I think they liked the bit of extra sunlight, and I must say that horse manure is the fastest drainage improver in clay that I have tried to date. Believe me, I have tried an awful lot of them.

Thanks for the heads up, Gardengal - I printed the link but didn't read it closely, I'll have to take a good look at it.

The link wasn't meant to be gospel! Just an interesting and somewhat helpful link. And, it isn't the only place I have read about the vermiculite nutrient holding capacity.
I didn't mean to mislead anyone by its contents. I just found it helpful myself, being a newbie gardener. :)

I really should have added above that in my experience, success with Heuchera depends greatly on the cultivar. I've found only a few that survive more than two seasons in my garden - all the other cultivars have petered out over the course of time.

Great info. As for adding perlite to garden soil, i don't add it intentionally to my garden or my compost, due to the fact that if used in my beds, it has a tendency to float to the surface and to me it looks unnatural. Some always gets in with transplanting, and that's fine. I think in my case i will add some coarse sand and compost. If anyone on here knows anyone who lives where heucherra are indigenous, I would love to hear about the soils they prefer. Pictures of wild heucherra might be worth a google.

Lots of composted cow manure. I added it last year to a new Heuchera bed and I've never seen such great results.