male seaberry

three years ago (2021) I purchased two female and one male seaberry/Sea buckthorn plants, females did fine but the male died.  In 2022 I purchased two males and a female, again the female is fine but both males died.  in the fall of last year I purchased another female and two males, today I noticed one of the males looks like it will die, the female is fine.  They are planted in three different, but close, places.  All four females are fine, the older ones are suckering, but of the 5 males I have planted only one currantly appears healthy.
I live in one 7a with hot humid summers, sandy loam soil, native ph is 5.9, no standing water, planted on a slight slope.  None have ever been very dry.  first three were planted on a berm, soil was amended with organic material, lime as per soil test and were kept watered.  Nursery suggested that I overwatered and to allow to dry 2-3" depth before watering.  Second batch were planted on a little more slope minimal amendments but were mulched heavily with wood chips, only watered when surface was dry at 2" or so.  Third batch on a little bit more slope and I dug a ditch on the downhill side of the bed (4' from the plants) to make sure drainage was good.  We have had lots of rain this year so have not watered at all, soil has stayed moist.  

All the males have died during the summer after having growth during the spring/early summer.  I am beginning to suspect the males cannot tolerate the temp/humidity.

I have spent quite a bit of money on a questionable fruit and if the last male dies I will have 4 worthless female plants.  I guess I can use them for nitrogen fixation/chop&drop but don't like their propensity to sucker.
Any suggestions or comments concerning why the males are dying would be appreciated.

Did you get all the male plants from the same supplier? If yes, they might all be clones of the same plant. You might try sourcing a male plant that is unrelated to the previous male plants.

no, three different online nurseries.

There are two reasons why your males die: they don't like to underground, or they don't like the above-ground conditions.

If your lonely male grew well enough that you can remove a part, could you try grafting it onto a locally well developped sucker?

Joseph's point of the same genetics might still apply even though it is a different supplier. Was your male a named variety?

I had to check my notes and then the websites, but none were named varieties of male.
Grafting is a great idea, wish I had thought about it.  I am a novice at grafting but have had good results with what I have tried.  Are seaberries hard to graft?  I would guess that it is to late to try this year, is that correct?  Could I try to T-bud or chip graft at this time of the year?

I have grafted many species, but never sea buckthorn so far. A quick google search just returned generic AI nonsense, I don't have access to my resources right now, but would try. I had good success with apples, pears, and plums in august, as long as the scionwood was fresh.

Cliff England in McKee KY told me his seaberries died in the hot humid summer. They get in the high 90s there or 100 at times.

They do want a lot of sun, but perhaps letting them get some afternoon shade say 3-4 pm in the summertime could help them with the heat stress. They do great for me here at 1800ft in southern wv exposed all day, but we don’t get above 95 degrees, and usually stay in the mid to high 80s in a hot summer. What is your 7a climate like?

I have heard males are more sensitive than females, and I know there can be a lot of genetic diversity amongst males. In our climate we probably want more northern Eastern European varieties rather than Mongolian. I have a male from one green world that has been doing great for me. Little slower to take off but now is quite established two years later. Moving them to a new location for the first time tomorrow. I’m guessing this male is the one they use to globally propagate, or perhaps they have a few varieties. It is a ready rooter via stool layering and fall softwood cuttings.

Do you have any photos of your plants? Are they growing very quickly?

We are probably a little warmer than where Cliff is.  He is a little north and at 600' or so more elevation.  It's common for the temp here in summer to be mid to upper 90's and over 100 is not uncommon.  The seaberries, have a burst of growth in the spring and early Summer but by august are looking a little sparse.  The single male I have survived the summer.  I am going to take a few scions this winter and graft to the females in the spring.  Females are producing a few suckers, if the male does better next year I will take more scions and try grafting to the suckers, and maybe placing those in a little late afternoon shade.  Since they are primarily wind pollenated I assume the males need to be fairly close the the females, it might be difficult to find a place to put several bushes that fit that microclimate.
If the last male dies I will take my loss and get rid of the females and replace with something more suited the my location.
I am out of town right now but I will post a couple of pics when I get home.   WE have only had one light scattered frost so far so they still have most of their leaves.

I had similar thing happen.  one male and one female from one green world.  Female looks fine.  Male dead.  Like the roots rotted.  Not even a year in the ground.  One thought is maybe the female was grafted onto a male and that will sucker.  Don't know.