Might have to do with your curing method, variety or storage conditions. I kept my 'Spanish Roja' in a cool, dry and dark spot in the basement after harvest and 3-4 weeks of drying. I planted mine 3 weeks ago and have about 75-80% sprouting. Could also be planting depth? hortster

It depends on your location and specific growing conditions, but Emperor 1 can reach dimensions similar to Bloodgood - in my climate, 30'x30'. And it grows a bit more rapidly than BG does as well.

Where do you live? France is a big place. And does it snow in your area? Here is some general info on lawns. Ignore your neighbor. He's trying to intimidate you and set you up to fail. Plant new seed only in the fall. Start in the early fall. That might be August or it might be September depending on where you live. You seem to have done it pretty well - perhaps by accident. Not rototilling was excellent. Rototilling is a big mistake that a lot of new gardeners make. See if you can rent a roller. You only need it once the first time you seed a big yard. After that, for annual overseeding, you can simply walk on the new seed to press it down onto the soil. Water new very lightly 3x per day, every day, until you get 80% germination. For the shade grass you planted that would be 3 weeks. If you have shade type grass, I'm assuming it's a fescue. Fescue should be mulch mowed at the mower's highest setting most of the time. If it gets hot in the summer, then mow every other week. The idea is to develop deeper roots to get water from deeper places in the soil. Fertilize for the first time on Fête du huitième mai or Jour de la Victoire 45 (same date different name). Fertilize again on Assomption and for the last time on or about Jour d'armistice. With the new lawn skip Jour d'armistice for this year. National holidays are easier to remember than specific dates. If you want to use organic fertilizer, you can do that any time including now. The application rate for organics is almost always 7 kg per 100 square meters. I like to use alfalfa pellets (lapin chow) as a fertilizer. Get them from a local feed store in 20-kilo bags. They really work. Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 3 cm all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps from 33-38 deep water once per week. With temps from 25-32 deep water once every 2 weeks. With temps from 21-24 deep water once every 3 weeks. With temps below 21, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. In the USA this deep and infrequent schedule works in Phoenix and in Vermont (for Oz think Hobart to Darwin including Alice Springs), so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall. These are in reverse order of importance. Watering is key to getting a good lawn with the fewest problems. Weeds: Spot spray a liquid herbicide in mid April and again in mid September.

Seaweed is supposed to have low levels of both auxins and cytokinin. They are also unstable and exposed to elements they break down quickly. I have not done what I suggested myself since I did not face a situation like yours. There are artificial cytokinins but they are tricky to use properly. The dilution has to be very precisely controlled. Nurseries and commercial growers use them in all sorts of fancy ways to increase fruit production. May is a bit late to ship bare-root but it is still OK. General rule for pruning deciduous/evergreen tree when they are growing is to prune just above at least one or two leaves or a branch with a few leaves. Otherwise it may end up in branch death. When they are dormant, you can be more aggressive with established deciduous plants as long as they are strong and healthy. I do that frequently. Scratch the bark off in a little spot in the top inch of the scion and see if you notice any green. If it is green the scion is still alive. If not then try a little lower. Use a knife to scrape the bark. I bet the bark is pretty thin and should scrape off. Since your scion is not showing any sign of growth, I would let one branch grow from the rootstock and keep that pruned to 5-6 leaves. Keep the height of the rootstock branch below the first bud on the scion. That will keep the juices flowing and feed the roots. If the scion is still alive it may push growth. I will be inclined to provide all day shade for that plant.