PK with 3 to 4 weeks of flower left

I've got to ask you all. I've heard people using PK boost for a week to 3 before harvest. I bought a nottle of Canna PK 13/14 yesterday and have to water today. The bottle says use for 1 week and I've heard of people using it for 3 weeks. Not having used it before, should I use it for a week and spend the remaing 2 or 3 weeks to flush? Thank you for any info!

I used their organic line before but never the PK boost. This is from their site;


The nutrients potassium and phosphate are indispensable for plants during their flowering period. PK 13/14 is a venerable potassium - phosphate mixture. PK 13/14 dissolves well and is therefore easily absorbable.

• Shake the bottle well before use
• Add PK 13/14 once to a full nutrition tank
• Dosage: 0.2 fl oz/Gal (15 ml/10L)
• Use for approximately one week only

Well according to them you're right; although 2 weeks of flushing seems too long to me.