@Bambarbia Thanks. I have quite a few grafted ones. Had no idea on cuttings. Some fruits take forever on their own roots. I was just having fun when I put them in the ground, but it is nice to finally see a fruit that is easy to propagate.
Also… many sources mention that Mulberry needs at least 400 cool hours in Winter in order to fruit. And some other sources mention that farmers in subtropics drastically trim their mulberries twice a year in order to have fruits twice a year 
and as you can see, my “Richters Nigra” seedling started fruiting under good fluorescent light in a basement, 6400K+UV, specialized grow light; no 400 hours needed. Less than 3 years old seedling. First fruits.
I have grafted IE (outside, in front-yard), second season: few small fruits; but this (3rd) season: huge 4cm-5cm delicious fruits.
I can verify the trimming trick. Did it last year. They will produce more, but not quite as much as the first round.
Bambardia, the substance at the bottom end of your Morus nigra cuttings is callus. This is the first stage of root formation. In a later stage this plant tissue will differentiate into plant roots. If kept under the right circumstances…
Morus nigra is usually propagated by summer cuttings of half lignified (green) young growth and rooted under mist. The second method which is only suited for hobbyists and not commercially viable is to root thick 4-5-6…cm thick pieces of wood harvested during late winter. These chunky pieces have a much higher rooting percentage than the thin cuttings of one year old lignified wood that you are using.
All other mulberry species can be rooted either by summer cuttings or winter cuttings but success depends entirely on the variety. Some mulberry varieties are very easy to root while others are almost impossible to root. This is genetically determined and has little to do with practical capability of the person.
So, what I mean is that however well you try to nurse your cuttings, success will always depend on the rooting properties of the individual mulberry that you are trying to propagate.
There is a Japanese mulberry germplasm database, of which unfortunately I cannot find the link anymore, where you can see the rooting capability of each of hundreds of varieties. Maybe the link has been removed or maybe the details of the germplasm database are no longer public…maybe someone can do some research…I’m not an internet specialist…
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