First of all there are 3 different type of feeding during the year, THey have different function and they have different sugar:water ratio.
You are here interested in spring feeding. The rule of thumb is to feed when the temperature during the night is over 0C. Doing otherwise may cause illness.
(Also the bees need to have honey protecting them from winter months both physically from the strong winter/ cold spring and to have food. Do not neglect this part and do not move brood outside of the protection of warmth that honey frames provides during spring months.) -had to add this part.
Now to move on the topic of WHY do you need to feed them?
You may need to feed them in order to boost brood production or for simple survival of the hive. If you want to boost the brood you use 1:1 sugar and water.
For all other ingredients see other beekeepers from your area. As for me I use some combination that may strengthen the resistances that were not mentioned above. For more info send me p.m.
If they do not have enough food you use 1.5:1 sugar: water. Enough food is 1 frame of pollen for each 1.5 frame of brood and border frames filled with honey at
almost all time. Boil the water, place sugar in it stir. Wait for it to cool and then add what you need. Serve only when it has less than 25C as it can also cause problems otherwise. Add all the other things once it has cooled down. Honey is not necessary and if you do not have your own DO NOT BUY it and give it to your bees. It may contain spores or bacteria that can kill your own bees!
Moving on, when you boost the numbers you need to know for what crops do you boost them. What can they gather. From what I understood you only have wild
grass. Bees do not need boosting for those crops. They gather them over time and in slow pace. Do not overdo it because then you will have a lot of bees that eat more than they can gather. Also on unrelated note having sheeps helps a lot. It is a healthy thing as they leave natural fertilizer behind them. Fertilizer = more flowers.
Next, if I remembered correctly you were thinking about some crops for your bees. The best I would recommend you is buckwheat. It gives nice amount of honey
and of course more seed. The advantage is that it grows on high altitudes VERY well. Focus on it. You may need a bit stronger hives for them. So you may feed your bees some 20-25 days before it flourishes. How much do you feed? 1dl/day for 7 days is enough to stimulate them to boost their numbers. That way they can gather 100% of the yield.
Hope this helps. I touched many subjects that are of great importance so feel free to ask on any of them if you need to. I will come back to forums this week some more.