Getting started with a planted tank: beginner questions and advice

[Luckyo]

I started cycling my second-hand tank at the beginning of December, got it from a mate.
Added a few plants, just stuck 'em in the gravel.
NT labs plant boost was a game-changer for the first few weeks, really helped 'em take off.
Two photos, 25 days apart, you can see the difference.

Don't wanna use plant boost now I've got fish in, and I'm not running C02 or any of that.
Is there something more natural I can add to help the plants along?

Also, took some cuttings from my other tank, anyone know what plant this is?

[dungeon]

To be honest, I'm not a fan of 'liquid carbon' either, especially when fish are in the tank. Your plants should do alright with the CO2 in the water, and with respiring fish, they'll get a bit more. I'd go for a comprehensive fertilizer, Seachem Flourish is a popular one - it provides the nutrients lacking in tap water. It doesn't contain nitrogen or phosphate, as these will come from tap water, fish waste, and leftover food.

[barbie]

Considering your setup, I'd recommend using root tabs for your stem plants - they'll be a great addition to help with growth, especially since you're not using C02 or any other supplements at the moment.

[dungeon]

If you're in the UK, I've had great results with TNC, might be worth checking out their TNC Lite.