The best replacement for greenhouse is cold frame.

The best alternatives to greenhouse are rated as following:
★★★★★  cold frame
★★★  garden
★★★  hothouse
★★★  conservatory
★★★  polytunnel
★★★  hoop house
★★  nursery
★  hot house
★  sunroom
★  coldframe
★  bedroom
★  enchanter's tower
★  potting shed
★  solarium
  hoophouse
  bedroom skyrim
  high tunnel
  green house
  greenhouse effect
  icehouse
  shadehouse
  lumatek
  garden shed

Your alternative for greenhouse is not listed? Suggest!
Speaking about greenhouse, one probably shouldn't forget about shed.

Other search terms related to greenhouse and their ratings are:
★★★★★ shed
★★ shed storage
★★ potting shed
You have in mind a companion for greenhouse and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of greenhouse in all years. Click on graph for more.
greenhouse
cold frame
garden