Broad global economic expansion is making assets expensive, so forget investing passively, an investment manager told CNBC on Thursday.

Instead, he recommend considering niche growth areas like avocados.

“Be very specific about what you do. Look for idiosyncratic, value and unusual niches rather than broad assets and broadly passive allocation,” said Stephen Diggle, founder of Singapore-based Vulpes Investment Management.

The firm has invested in agriculture since 2009, putting money into avocado and kiwi cultivation in New Zealand, Diggle told CNBC on the sidelines of the UBS Global Family Office Conference in Singapore.

Agriculture has “got some very good yield characteristics unlike global bonds. It also has some good inflation protection, especially unlike bonds,” he added.

In the case of avocados — for which millennials have a taste — Asia is also a huge growth market, Diggle said.

“Hong Kong and Singapore act as the harbingers of what broader Asian consumers do. And right now, Singaporeans and people in Hong Kong are eating avocados and we’d expect more and more Asian consumers to do the same thing,” said Diggle.

“Income generation from a successful orchard would be way above what you can currently get from a portfolio of safe, low-risk bonds,” he said.

Vulpes has also invested in cyptocurrency — even as founder Diggle said the space is probably in a “bubble.”

“We have a specific strategy, separately investable, that’s an arbitrage strategy in cryptocurrencies,” he told CNBC.

“Now for us, the cryptocurrency bubble — and it probably is a bubble — is an opportunity to find widely dislocated prices in essentially the same thing,” he added.

“Bitcoins don’t trade the same on exchanges, they trade at wildly different prices. Last year during the massive ramp up, you could find the same bitcoin trading at 20 percent difference in price in various parts around the world. That for us, creates opportunity,” he explained.

Still, Diggle said he was a “skeptic” of cryptocurrencies, but the excitement around the virtual assets generates investment opportunities.

“In the second six months of last year when a lot of people were making money trading long, we made 50 percent by being totally flat,” he said.