G	Growth	Grows faster.	0.6
Y	Yield	More harvest per plant.	0.6
H	Hardiness	Copes with bad light, temperature and water.	0.6
W	Water	Drinks more water.	1.0
X	Empty	Does nothing.	1.0

How a cross works

Every plant has six gene slots. Early in its growth it crossbreeds once with the plants touching it. Each slot is decided on its own.

1. For that slot, add up the weight of each gene across the neighbours. Green genes weigh 0.6, red genes weigh 1.0.
2. The heaviest gene takes the slot, but only if its total is higher than the weight of the gene the plant already has there.
3. If two genes end on the same total, the game picks one at random.

That is why one bad neighbour matters: a single W (1.0) beats a single G (0.6). You need two G neighbours (1.2) to push a W out.

Getting it right in game

1. Use a large planter. The centre spot touches all eight others, so it is the only spot the planner uses.
2. Plant the centre first. Wait 10 to 15 minutes, until it is about halfway through the sapling stage, then plant the donors around it.
3. The order matters. A plant crossbreeds once, when it reaches the crossbreed stage (around half an hour after planting). If the donors went in first, they would crossbreed with each other before the centre does, and the centre would copy their changed genes.
4. Growth speed depends on light, water, temperature and G genes, so treat the times as a guide. What counts is that the centre reaches the crossbreed stage before any donor.
5. Once the centre has passed the crossbreed stage its genes are final. Check them before you clone.
6. Clone the good ones. Clones keep their genes, seeds do not.
7. Where the plan shows a chance under 100%, plant a few planters with the same layout.