Question
How do you know when the seeds on lilacs or roses are "ripe", or when they should be removed from the plant to have the best chance of germinating?

Answer
Hi Terry,
Thanx for your question.  The lilac seed capsules will turn brown and I would pick them quickly before they start to open.  The rose seeds are inside something called a "hip".  They look like tiny crabapples, sort of and are usually red, pink, orange and rarely, yellow-orange.  They are usually ripe in the fall.  If you don't have a bird problem, you can usually start picking rose hips for seeds right before the first frost.  Bear in mind both seeds require cold stratification for germination and some roses require more than one season in order to germinate.  I hope this helps.
Tom