Calico Publishing, which owns the UK's biggest pet products portal, plans to relaunch both sites within two weeks.
Kevin Hague, founder of PetPlanet.co.uk and Calico Publishing, claimed he could make both acquisitions profitable within 12 months, using the lessons PetPlanet had already learned about "tight cost base management and smart marketing".
Hague said Thinknatural would be trading again by next Monday, and Greenfingers would be live by Friday and trading in two weeks.
He refused to reveal a marketing budget for the relaunches, but said Calico believed in 'smart marketing' rather than big budgets. This will include deals with search engines to flag up the sites when consumers search on gardening and health topics and content deals with other portal owners.
The first marketing project will be the publication of Greenfingers' summer catalogue, which will be inserted into up to two million publications.
Hague said the success of that catalogue would set the stage for Calico's future strategy for both sites.
"We are not against doing things in print, but the economics of online retailing are so much more favourable.
He said Thinknatural was the closest to breaking even as a purely online business.
While each of the three sites Calico owns will be run as autonomous business units, they will benefit from shared warehousing, a single call centre and other synergies in technology and distribution.
Hague said he intended to meet Carol Dukes, the founder of ThinkNatural, to discuss the site's future. "Carol Dukes has been out of ThinkNatural for a while now, but it still carries her personality to some extent and I think it would be good to get to know her better."
Greenfingers.com launched in January 2000 and Thinknatural went live in 1999.