Solutions for continuing orlah count for citruses growing abroad

Question

Hello Rabbi, Thank you very much for the information and guidance that you provide. I am growing citrus trees from seed in chutz la’aretz. At this stage, they are being kept in containers for practical reasons while they are still young, with the intention of planting them in the ground once they are more mature and closer to fruit-bearing age. At present, some of the trees are in 1-gallon containers and some are in 6-gallon containers. As they grow, we expect to move them into larger containers, likely in the 15- to 25-gallon range, before eventually planting them in the ground. The containers are plastic and do have drainage holes already, and if necessary we can enlarge the drainage holes to approximately 2.5 cm. We built a screened enclosure on our concrete driveway in order to protect the trees from the Asian Citrus Psyllid, the insect that spreads citrus greening disease. The screenhouse has only a mesh roof and no permanent solid roof, so rain and sun pass through it. My question is primarily regarding orlah. I would like the arrangement to count both while the trees are still in pots and later when they are planted in the ground. My concern is whether the trees are considered disconnected from the ground because the containers are resting on a concrete driveway. I would like to know whether there is a halachically valid way to create a sufficient connection to the ground so that the containers would not be considered as being on an unconnected surface. One possibility I am considering is drilling a hole through the concrete driveway down to the soil beneath it, and then covering the floor of the screenhouse with a layer of soil, so that the pots would sit on soil that is connected through that opening to the earth below. Another possibility would be to create a connection between the soil placed inside the enclosure and soil adjacent to the driveway. The containers could either sit directly on the soil, or, if halachically acceptable, they could be suspended slightly above the soil on blocks or on some kind of perforated surface, such as a mesh table, with open view to the soil below. Would either of these solutions create a sufficient halachic connection to the ground for purposes of orlah? If so, are there specific requirements regarding the size of the opening/hole that is drilled in the concrete, the drainage-hole size in the containers, the thickness or continuity of the soil layer, whether the pots must rest directly on the soil, or whether a perforated surface above the soil would also be acceptable? Thank you very much for your time and consideration.