It's short for dekagram (English decagram), often abbreviated as 'dag'. 1 dag = 10 grams.

Dekagram is a weight unit. In recipes it's shortened to dag, (t, kg, dag, g, mg etc.). Deko and deka are used interchangeably (and are incorrect according to wikipedia, we don't really care), guess they don't have any basic form. You can't decline deko and deka: M: pięć deko truskawek, N: pięcioma deko truskawek M: pięć dekagramów truskawek, N: pięcioma dekagramami truskawek

Really? Firstly, in my book I see "deka". Secondly, we say "dekAgram", not "dekOgram" So logic question: why DEKO?

You have to say: 25 deko ziemniaków. Basic word is DEKO, from dekagram