Today i saw spidermites on my plants and freaked out , i never thought they would appear on a terace.
Is there a cheap way to kill them or are there plants that repell them?
Are their like portions that make plant leaves resistant against them?

Just plain old soapy water in a spray bottle will kill them. 1/2tsp. dish soap to a quart of water (stronger is NOT better!). Be sure to spray all parts of the plant - stems, leaves top and bottom and the surface of the soil too. Rinse the plant off with plain water after a few minutes - the soap will make the leaves sensitive to the sun if you leave it on there. Repeat the treatment in about a week, to get any that have hatched from eggs left behind - the soap kills the live insects but not the eggs.

After that to keep them away just spray the whole plant regularly with a hose or spray bottle of plain water. The plant will love this treatment, and the mites hate it, they either die or are washed off the plant. They don't like wet weather, so if your terrace gets any rain that will help.

Mites thrive in warm, dry conditions, so potted plants that just get water poured into the pots are very susceptible.

but I would use that soapy water twice a week. Those little puppies hatch in 3 days then grow up and become sexually mature in another 5.

Spider mites thrive on dry heat and dust. I think they wonder in on the breeze.

You can use diluted soybean oil for spider mites - more info here:

http://hriresearch.theknowledg...

I'm not a fan of using anything oily in hot weather. I use dormant oil spray on my orchids but only in winter if the weather is really cool, highs below 70F.

You'd have to leave an oil spray on to smother new generations or use it again and again, same as soap. Plus you'd also have to wash it off the plants so they wouldn't become photosensitive.

I'm a BIG fan of the KISS theory. Plain old soap works well, for an initial infestation and then just spraying with water keeps them away beautifully in my garden.

Quoting from the research link above, this was tested in summer: "This research shows that summer sprays of soybean oil effectively controlled populations of two-spotted spider mites with minimum phytotoxicity to burning bush plants (Euonymus alatus Thunb. Sieb.‘Compactus’). A single spray of 0.75 or 1.0% or two sprays of 0.25 or 0.5% soybean oil gave effective mite control."

Soaps can be damaging in hot weather too and some plants are particularly sensitive to soap sprays. We don't know what plants have the problem or where foussi is, might be winter there With both oil and soap sprays it's a good idea to test treat a plant it hasn't been used on before.

In the link to an article on spider mites by entomologists that I gave in another thread the other day, it was noted that horticultural oils used at the “summer oil” rate are "perhaps the most effective miticide available for home use." For insecticidal soap they noted "marginally effective against twospotted spider mite and where webbing prevents penetration."

http://extension.colostate.edu...

This article on insecticidal soap lists some of the sensitive plants.
http://www.clemson.edu/extensi...

I just realized my plants have spidermites because have no wind .
Its like 30° and there is no air circulation.
I was able to kill the spidermites by washing them off.

Diatomaceous earth works great, just have to reapply after it rains.

You have to be careful using DE outdoors though. It will kill beneficials, small butterfly caterpillars and bees, too. IF it's an indoor or, as in foussi's case a terrace plant isolated from the outdoors then not a bad idea. I only use DE for ants, keeping it indoors, and on the floor.