The 406 plug flat is often used because it is small enough for economic production while providing enough space for growth until transplant. However, larger plug sizes can be used to meet special production goals. Medium pH should be 5.5 to 6.0. A pH below 5.0 inhibits germination by as much as 60 percent. The thin layer of vermiculite allows the light some Impatiens seed needs to germinate to reach the seeds while maintaining adequate moisture around the seed.
Temperature is critical for rapid, uniform seed germination.
Maintain a medium temperature of 72 to 75 degrees F for the first 7 to 10 days or until radicals emerge, then 68 to 72 degrees F night and 70 to 75 degrees F day temperatures for seedling growth. Germination temperatures that are too high or too low can reduce germination rate. Water temperatures for irrigation and mist should be 70 to 78 degrees F to ensure that medium temperatures are high enough during germination. Night temperature can be lowered to 60 to 62 degrees F in the last week of plug production to tone the seedlings and prepare them for shipping and transplanting. Impatiens seeds require close to 100 percent relative humidity for rapid, uniform germination.