Here's something that popped into my head while still half asleep. Add cross pollination to the new plants but in a slightly different way. All the new plants would produce pollen and you could attempt to cross them and would produce only 1 seed, to keep the need to hunt for seeds. Only some of the plants would produce a plant seed others would produce a grass/weed seed. Poppies and Snowdrops (crossed either way) would produce 1 seed each. 50% chance at the spread Campion flower, 50% chance random grass/weed seed. Tall Hedge and Short Hedge (crossed either way) would produce 1 seed. 25% untrimmed short hedge, 25% untrimmed tall hedge, 50% chance random grass/weed seed. Cypress tree and Mossy Cypress tree (crossed either way) would produce 1 seed. 50% chance date palm seed, 50% grass/weed seed. Cypress tree and Cocoa tree (crossed either way) produces 1 seed. 50% coconut tree, 50% grass/weed seed. Mossy Cypress and Cocoa tree (either way) produces 1 seed. 50% banana tree seed, 50% chance random grass/weed seed. Hops (left) and Hops (right) (crossed either way) 25% small hops (left), 25% small hops (right), 50% random grass/weed seed. Maybe a few others could be cross pollinated to produce plants too then whats left would would produce a random grass/weed seed 100%. Anyway.... a Happy New year to you all.