I don't know who presented your class but he/she is wrong on several points.
All hostas grow better...faster...in the sun. Some "burn out" but given enough water the plants will grow more rapidly in the sun...but....there are some varigated hosta that will become really ugly in the sun...like Frances Williams, and some solid green hosta do very well in the sun...like krossa regal.
Slugs may be less of a problem with rock mulch....but there will be many other problems that will off set any advantage. Hosta like soil rich in organic matter, they do best when top dressed with compost....an impossibility with rock mulch. Slugs are best eliminated with a non toxic bait like Slug-go. Serious gardeners never use rock mulch for anything but a cactus garden.
June is not the best time to transplant and divide hosta....early spring, just as they are emerging is best..like late April. Next best time to divide is about 6 weeks before the ground freezes...like early to mid September here in Iowa.
Most hosta are not deep rooted...but their roots spread widely.....that's why it is important to water them well.

I have been growing hosta for 32 years...in Iowa. I seriously doubt that they are the number one selling perennial...but rather the perennial which has the most new cultivars introduced every year ( day lily formerly held that position).
There is a hosta forum here....and many Iowans post there. follow the link below, see what the knowlegable hosta growers have to say....then go back to your master gardener and set him straight.
Linda C

Here is a link that might be useful: hosta forum

Yikes Linda, are you always this harsh?! LOL First of all the presenter was *not* a master gardener. I won't get into it with you about his credentials, but he was more than just knowledgable, ie: he was formally educated.
We learned so much, and in such detail, that it's easy for me, a hosta novice, to see much of what you've refuted is just opinion.
This presenter shared his passion for hostas in such a way that it was contagious; everyone went home wanting more. I just wanted to share a little bit of that excitement here.....

I tells it as I sees em! LOL!
Sorry it seemed harsh to you but I have little patience with the spreading of false ideas and methods for gardening.
The Hosta bug has bitten me...big time. I have spent a lot of time reading, researching, learning, asking....and yes buying and digging.
I would hate for someone to think that a rock mulch is best for hosta, that they must wait until June to transplant and planting Montana Aureomarginata or Frances Williams in the sun is a good thing, and not realize that some hosta have very shallow roots.
Hosta are amazing plants with their huge variety and their hardiness....it's hard to kill a hosta, ......and very easy to make them grow to big beautiful plants. The vision of a 5 foot clump of Sum and Substance glowing under a clump of trees is truly a wonderful thing, I understand the excitement.
If you really want to catch the fever, check out the hosta forum on this site. There are many very knowlegable gardeners posting, and many pictures of wonderful hosta gardens.
Linda c

Linda I did check the hosta forum specifically the FAQ section and I saw nothing that disagreed with what I was taught or posted :)

Whatever......go right ahead and mulch your hosta with rocks, plant the yellow ones in the sun, dig and divide in June so they can look ratty the rest of the summer. You heard some guy give a talk so you know all about growing hosta, I won't agrue. I just hope others reading these forums realize that other people have different thoughts about growing hosta.
Linda C

I also LOVE hostas and lurk on the Hosta Forum often. I thought I'd throw in a few comments! I am glad to see that your speaker was spreading his enthusiasm for hostas! It is a growing interest amongst gardeners, so it would not surprise me if it is the number 1 selling perennial.

I do believe that your speaker was providing some very general ideas about hostas and a literal interpretation can cause some difference in opinion. For example, some white striped or centered hostas will "melt out" if placed in too much sun.

Your speaker had some great points;
"Yellow" and many "white striped hostas tolerate sun quite well,"
"the very same varieties of hosta may be greatly different in color, depending on how much sun they get,"
some hostas "roots go very deep -1½'- so water them well.. especially ... in the fall.."

To clarify some points;
Hostas are "shade tolerant" not necessarily "shade loving." However, some variegated hostas (like Frances Williams & White Christmas) will look very poor when placed in even a small amount of sunlight.

I would never mulch my hostas with rock. Mulch helps keep the moisture in the soil which is very important for hostas. A better slug control alternative (in my opinion) is an Iron Phosphate based slug bait that is environment, pet and kid safe.

I would also have to agree that, although hostas can be transplanted and divided successfully at any time of year, you'll have better results in the spring and fall.

Thanks for sharing with us! If you want some ideas of hostas to add to your own collection, there are some wonderful pictures of hosta gardens posted in the Hosta forum under the thread "Post pics of your hosta beds."

-Pam

I think that the most important thing here is that SOS Acres, Lindac, twin too, and probably a lot more of us just love hostas!!! It's always good to get differing opinions and visit with folks that have grown hostas under varying conditions. I practice the philosophy that it can live or die and if it dies it can be replaced. I get a lot of first hand knowledge of what not to do again that way. :) Happy hosta hunting!

Diann
IA Z5a

S.O.S., I thank you for taking the time to report your new knowlegde. I'm just curious, Are you a Master Gardner? I'm in the process now. I have about 5 more classes. I have the 40 hours of volunteer work in. I've wanted to do this for years. I'm real anxious to meet other Master Gardners.

I appreciate Linda's efforts to "get the facts straight." I've been growing Hostas for nearly twenty years, and what she says seems to be the rule for MY experience, too.

Just because one corrects an error of fact doesn't mean one is "harsh."

Sanfan, We are Master Gardener Interns too! Tuesdays we have ICN classes, Thursdays a "live" presentation. November 9 will be our last class. Will you go to Iowa State University next weekend (or this weekend) too? I'm impressed that you have your hours in already, we are just getting started. There's a new forum here for Master Gardners, didn't notice anyone from Iowa tho. Glad to meet you :)

Actually, hostas ARE the number one selling perennial in the US and have been for a few years.
There are now about 1500 daylilies registered each year with AHS (that's American Hemerocallis Society), and I seriously doubt there are that many hostas registered each year.