Every Christian will bear spiritual fruit. Somewhere, sometime, somehow. Otherwise that person is not a believer. Every born-again individual will be fruitful. Not to be fruitful is to be faithless, without faith, and therefore without salvation.
Having said that, some caveats are in order.
1. This does not mean that a believer will always be fruitful. Certainly we can admit that if there can be hours and days when a believer can be unfruitful, then why may there not also be months and even years when he can be in that same condition? Paul exhorted believers to engage in good works so they would not be unfruitful (Titus 3:14). Peter also exhorted believers to add the qualities of Christian character to their faith lest they be unfruitful (2 Peter 1:8). Obviously, both of those passages indicate that a true believer might be unfruitful. And the simple fact that both Paul and Peter exhort believers to be fruitful shows that believers are not always fruitful.
2. This does not mean that a certain persons fruit will necessarily be outwardly evident. Even if I know the person and have some regular contact with him, I still may not see his fruit. Indeed, I might even have legitimate grounds for wondering if he is a believer because I have not seen fruit. His fruit may be very private or erratic, but the fact that I do not see it does not mean it is not there.
3. My understanding of what fruit is and therefore what I expect others to bear may be faulty and/or incomplete. It is all too easy to have a mental list of spiritual fruits and to conclude if someone does not produce what is on my list that he or she is not a believer. But the reality is that most lists that we humans devise are too short, too selective, too prejudiced, and often extrabiblical. God likely has a much more accurate and longer list than most of us do. Nevertheless, every Christian will bear fruit; otherwise he or she is not a true believer. In speaking about the Judgment Seat of Christ, Paul says unequivocally that every believer will have praise come to him from God (1 Corinthians 4:5).