Striking Piper seeds can be a very slow and frustrating process.
The seeds do not normally have a double dormancy but must be treated as if they do.
Seed is best sown into seed pots or punnets and moved on to larger pots once the roots have started working. Sowing into flats can cause many problems as it is very difficult to move an established seedling without disturbing un-germinated seed.
Germination is sporadic and varied which can be inconvenient.
Once germination has occurred, you may be faced with one or two leaves only. This may not change for months.
Sometimes, the leaves continue to grow to a very large size before the plant will send forth new leaves. Some will grow a good climbing stem and others will simply stay short and leafy.
There does not seem to be a pattern in this behaviour.
As soon as the plants show good vertical growth they should be encouraged to grow on a support.
Lateral growth should be encouraged at this stage.