Certified GKH Gardening Expert
Not necessarily, but planting them close together makes it easier for them to spread if the plants do get aphids. Plus, lack of air circulation can promote fungal diseases.
Many baskets purchased with million bells are planted closely because they contain several colors. If you are planting in a garden, you can plant them further apart. In a 12 inch basket or container, I suggest planting no more than three small transplants.