Hardiness Zone 7a
Location: Surrounded by Fields, 219-223 meters above sea level (minimal slope from west to east and north to south), windy location, full sun
Soil: Medium heavy loam, pH: 6,5-7 (Ill send some soil samples to a company so i know how the quality is)
I’m doing something pretty big next year. I’m removing a conifer collection and putting in rows to plant fruit trees. I’m going orchard style with posts and wires and spacing between rows of appx. 3-meters. I’m going to prune with spacing between trees of appx. 1.5 to 2 meters and a height of 3 meters. It’s going to look awesome from my kitchen window because I’ll be looking down the middle of each row. 3/4’s an acre or thereabouts.
Like this: with wires on each side of the trees with the trees in the middle.
I don’t think you will have compatibility issues with myrobalan for your gages and would give them a chance.
I would stay away from St. Julien if you don’t have your orchard close cause they are struggling in our summers.
If you don’t water frequently the growth will be minimal and the leaves will look in August like in November (my own experience). I would also advise against using VVA-1 (Krymsk 1) or Wavit/Wangenheim although I heard about a new Wangenheim strain which I cannot remember the name of, that’s good for our conditions. I am slowly replacing all my Wangenheims with myro/myro Cs. It all depends how much time you have. If you have your orchard behind your house, fertilize/spray/water regularly, keep the area around the tree free of grass, those are good rootstocks.
If you can get to your garden only every 10-14days for a short time and it looks like a jungle they will suffer.
My M9 apples I keep around the house look all great with a lot of growth. Those planted in my orchard are pity to look at. You don’t have to worry about space, 4m is plenty, so pick something vigorous, it will save you some headache
I never heard about gages being incompatible with Myro, and Myro is probably the most common RS for gages in the US. I would speculate that the observed incompatibility might be due to some latent virus in gage scionwood which occurs in Europe but does not exist or is uncommon in the US. This situation might be akin to Prune Brown Line Disease that is associated with tomato ringspot virus (see http://ucanr.edu/repository/fileaccess.cfm?article=72348&p=JLDMMJ)
Mulberries and native persimmons tend to require more room than most common tree fruits on typical “semi-standard” rootsock (apples on 7 or 111).
I wonder why you focus on gage plums- there are so many other wonderful E.plum varieties that are often easier to grow, more reliable producers and more useful from a culinary stand point. People love my Green Gage plums, but love my Valor, Castleton, Empress and others just as much, or more.
One piece of advice I can give you that I’m sure you would ultimately appreciate is to pick varieties that stagger the harvest as much as possible.
I love only very sweet plums also, and the varieties of prune plums I and many on this forum grow get sugar at least as high as gages. Sugar content is not what differentiates these varieties as a group. Perhaps you had a Stanley plum, which some years here fall from the tree while still green and never get the fully sweet, amber colored flesh. It is often sold as Italian.
If you fail to consider the relative difficulty in growing varieties and the reliability of their cropping in your region, you will likely end up wasting time and switching varieties over. Been there, done that.