Silymarin is the main component of Silybum marianum, which means 5.9% is quite low. 

How much do you expect?

In the following paper may be reported some of your interest. 

Ind Crops Prod. 2016 May;83:729-737. Epub 2016 Jan 5.

Silymarin content in Silybum marianum populations growing in Egypt.

AbouZid SF1, Chen SN2, Pauli GF2.

of the organic extract i would expect more than 30% to be silymarin compounds.

My HPLC result is as follows:

taxifolin 21.37  - Silychristin 31.88 - Silydianin 3.59 - Silybin A 0.24  - Silybin B 1.90 - Isosilybin A  0.15  >>>>> Silymarin 59.13 mg/g dried extract

Any idea?