water catchment tires for elderberry cuttings- ideas?

GOAL: create an elderberry field.    I have an outlying field.  Tires are placed in rows to surround elderberry cuttings (365).  Cuttings are stuck into the ground in April- zone 4.  If we don't get enough rain in spring, the cuttings will not root.  

Solution:  create a water catchment within each tire, like a tire funnel.  My thought is to place a garbage bag over each tire, poke a hole at the base where the cutting is.  Rain water is caught & funneled directly to the cutting.  This way I am not spending ridiculous hours of time/energy shlepping water to 1.5 acres of elderberries, which may consider growing.  Bags would reduce impending weed pressure as it covers the ground.  Also, covers openings which invite wasp & snake habitat.

Challenge:  #1 garbage bag openings are too narrow for tires (26" diameter); #2 bags need to be anchored to withstand wind issues;

Creative People! can you help me brain storm a solution for keeping these elderberry cuttings alive as they take root the 1st year?  Thank you for your input!!

That is a LOT of elder!!

Do you have a plan for how to use it all? We made a household supply of elderflower syrup in two batches from one single elderflower bush.

Personally I would try to avoid all tyres and plastic. You'll be stuck dealing with them years later.

An alternative is to use planting holes or swales to collect and sink rainwater. Planting each bush slightly below ground level in a small hollow allows for fast watering.  You can dump a bucket in each hole, without it flowing away over the surrounding soil. But still, any manual watering of trees on that scale is an epic task and to be avoided.

Do you have access to large quantities of mulch? Thick mulch around the plants will help preserve water in the soil between rain events.

I love elderberries!  So many reasons to grow them, but that’s a LOT of elderberries!

Is there some reason you want all those separate trees? Elderberries self propagate by putting up new shoots, expanding outward from the center. You could have clumps of elderberries in the center of those depressions in the soil.  

Another strategy is to just start a dozen future clumps and get to know everything you can about elderberries.  In a few years you should have transplantable shoots to fill in your field.

Broader depression of same gradual slope will yield deeper depression, funnel more water to the center, and make more room for a greater volume of chips.

I also, would avoid the use of tires and plastic.  For the reason noted above, as well as the pollution factor of all plastics everywhere, both the resources used in their production, and the products of their decomposition.