Growing a Telegram channel for free: post swaps
The most effective free method for small Telegram channels is swapping posts with channels of similar size and topic. Also: cross-link from your other platforms, post at a consistent time, pin a short "what this channel is about" post, and repeat the formats that bring subscribers.
Disclosure: I'm on the Trigram team (trigram.site). Trigram has free cross-promotion: pick a partner channel in the catalog, agree on a time, and the bot publishes both posts and checks they stay up. There's also Trigram Lens, a free Chrome extension with public channel stats.
Guide: trigram.site/en/grow-telegram-…
Cross-promotion: trigram.site/en/telegram-chann…
Lens: trigram.site/en/lens