You forgot to buy a new bottle of detergent - so why not mix what's left with some fabric softener? Actually, there are several reasons why that's not a good idea.
One is that the mixture won't effectively clean your clothes. Plus, it doesn't dissolve well in water and can clog the fabric softener compartment, according to German detergent association IKW.
Fabric softener should only ever be added to the fabric softener drawer by itself from where it enters the drum during the last rinse cycle. During the previous cycles, most of the dirt and also detergent residues are removed from the textiles.
Don't put detergent in the fabric softener drawer
Detergent should never end up in the fabric softener compartment. For one thing, it would miss the actual wash cycle.
Putting detergent in the wrong compartment can also result in detergent residue remaining on the fabric, which can cause skin irritations, according to the IKW. Fabric softener, on the other hand, is made to form a protective film over the fabric's fibres.
Don't use universal detergent for wool
You should be extra careful when machine-washing garments made from wool. Always use a special wool detergent instead of ordinary heavy-duty or colour detergent, otherwise you might damage the fabric.
Wool detergents don't contain any optical brighteners, bleach or enzymes, according to the IKW. These would break down the protein compound that wool and silk are made of. In addition, normal soap suds tend to felt wool, decreasing the softness.