Yes, I've used the sweating technique several times with no success. I also use Rhizotonic, etc as recommended by Harry Harrington. I wonder what exact species you're collecting in the US though? I'm referring to Crataegus monogyna. I've found Elm to be extremely easy compared to Hawthorn.
Actually ALL of the hawthorns I’ve collected are
monogyna. They’re not native here but are naturalized and have been for a couple hundred years probably. You know, the English brought a lot of things with them when they showed up ?. In fact they are just as common or more common than our native hawthorns in a lot of areas. Tony Tickle is British and all his articles on sweating collected hawthorns are mostly with
monogyna, I believe.
If you haven’t had success with sweating collected hawthorns then you are doing something wrong. It’s worth trying to figure out how to do it correctly, the results are phenomenal.
This is a picture of new aerial roots growing above the soil on a collected hawthorn of mine, a couple weeks after collection. This is due to the immense root growth you get from the sweating technique.
Pics of one of my single seed hawthorn,
Crataegus monogyna, collected last spring (2017) with almost no roots. Pictures taken today.
And yes, elms are easier to do anything with than anything else I’ve encountered. Pretty much bullet proof.