I treat my outdoor teak furniture with "Teak Oil" from Lowes every 8-12 months as needed.
Don't spray it, even though you'll want to. Paint it on, let it sit, then wipe it off/in.

I don't know how i got to this thread lol I was looking up how to set up grow lights.

Anyway, mislabeling is a constant source of irritation to me so I will pick this subject up even if it is a tad late.

For starters, if you bought your outdoor teak chair for less than, say, $800, that is more likely to be cedar with teak finish and not real teak. Real teak lumber costs about $40 per board foot. There is no way anyone can make a garden chair with real teak for less than $800-$1000 and that is probably conservative.

Second, cans of wipe-on finish sold at big box stores are usually a mixture of varnish, colorants and various other things to speed up drying when applied. Most of these products are conveniently silent on what they actually contain.

If your furniture is turning gray over time, it is most likely made of cedar as it is notorious for losing its nice golden color when exposed to the elements. It is in the nature of the tree itself---the same oils that make it impervious to various insects, fungi and what not make it vulnerable to the color alterations caused by exposure to UV light from the sun.

Finally, for furniture finish, boiled linseed oil is normally used. It penetrates better and dries much faster. Raw linseed oil takes longer than forever to properly cure and in the meantime you have to protect the piece from various gnats and particles that could land on it and get embedded in the finish.

Refined linseed oil, on the other hand, is significantly more expensive because there are extra steps required to make it. It's used mostly in oil painting, it makes pigment flow better and when it dries, the colors are nice and glossy.

I think you can cook with linseed oil too. I just haven't done it.

Actually, real teak ~does~ turn gray over time.