A toothed blade can be used when dealing with knots, but doesn’t need to be an expensive piece of additional equipment. This is what I do;
1. Prepare a spare 2″ plane iron in the usual way, then divide and mark the edge – using a sharpie – into 12.
2. Using a fine triangular file or Dremel cutting disc nick the edge so it’s grooved to a depth of 1/16″ – 1/8″.
3. Remove resulting burs from plane iron and re-fit the cap iron/chip breaker.
You now have a toothed blade that’s capable of dealing with gnarly grain and knots with, against, across or diagonal to the grain. It can be fitted into a #04 or #05 plane at a moments notice, or you can keep it fitted in a spare plane for the sole purpose of toothing problem surfaces prior to finishing with a smoother. 😉
Grooving a plane edge will not draw or damage it’s temper and is fully reversable via grinding back to create a clean edge.
Another option I favour is to grind a radius the leading edge of your #05 jack plane iron, creating a cambered edge. The curve/arc can vary, but I find an 8″ radius works well. This provides a cutting edge similar in nature to that of a scrub plane and is ideal when preparing rough stock prior to smoothing and works extremely well when encountering knots.
I hope this helps in some way.