The idea in question is for a gardening tool.
Most countries provide a search engine for their patent data. Additionally there are third-party search engines for patent data. Most of these will (all the big ones do) search the text of the patents for the supplied terms. Below are some links for the most popular tools. If you are looking for US patents, I would start with Google Patents first to get a sense of what's out there. From there you can get more detailed with the USPTO's site (which has a fairly weighty searching syntax). I don't search for European assets that much, but I generally used Espacenet.
- United States Patent Office
- Espacenet (Europe)
- Japan Patent Office
- A few others, just search for "[country] patent office"
- Google Patents
- Google Scholar (combines Google Patents with non-patent literature, e.g., prior art)
- Patent Lens
- Fresh Patents
- Boliven (note: Boliven is somewhat limited for free searching. The last time I used it I was capped at a small amount of searches. Their s
The best way to search if your idea has been patented is through the Google Patents application which can accept multiple names of ideas, synonyms and dates. For the link I provided, simply replace the words with descriptive words for your invention, for example, a Google Patent Search for "Shovel" and "Hammer" and "Garden" will yield accurate results, including this patent, which covers many 'types' of possible gardening tools:
An elongated shaft to receive a working head of a garden implement. The elongated shaft comprises a terminal portion sized to receive the working head of the garden implement, and measuring indicia applied to the elongated shaft over at least a portion of the length of the elongated shaft.