Half marathon training plan - fartleks and intervals

[Deleted User]

How often in a week should you do intervals/fartlek runs as part of a half-marathon training programme? My usual routine has been two short 3-5milers a week plus a long run on the weekend, plus Pilates or swimming, depending what my wrk schedule is. From reading bits and pieces on here, I know speed work is important, but how much should i Be doing? Shoud I do a fartlek and an intervals session? Also, would circuits and kettlebells count as Cross-training on non-running days? I want to get a balance and do enough effective exercise Thanks!