So I've chosen this question as I know A LOT of you who are new to planted aquariums, wonder how to plant aquarium plants. So I wanted to cut straight to the point and I have combined this post with a YouTube clip I made sometime ago now.
1) assuming you have purchased the plants from us, there is no need to clean under tap water - our plants DO NOT contain any pesticides or anything that would harm you tank inhabitants. So relax about that one :)
2) Remove the plant from the plastic pot and if you can please recycle the pot as most recycling centres now accept them.
3) You are now looking at your plants and on the bottom of it is rockwool. This is totally inert and safe for your tank. It's used so that the plants can root into. The easiest way to remove rockwool is to physically remove what you can by hand, and the remainder run it under tap water and it comes off very easily that way. If you are using plants such as Hemianthus then I recommend that you leave about 10mm of rockwool as this will help to anchor the plant down as they are very light and likely to bob up to the surface otherwise. For those of you unsure about this plant - it looks like this:
4) You now need to split your plant into several sections (if possible). Using Heminathus as an example, you can cut this with scissors into 5-6 pieces. Other plants like cryptocorynes you will be able to gently tease apart and plant as 4-5 new plants. But, not all plants can be split - most Echinodorus are only one plant and that is how they will stay.
5) Some plants will have a decent root structure to them, others will not. If the roots are big and you find they will get in the way, simply cut them off with scissors. Leave about 20mm - you will find this does not effect plants at all and can actually have the reverse effect and create positive plant growth. A bit like stemmed flowers - they're always trimmed at the base before putting in water to improve nutrient uptake and the same goes for aquarium plants.
6) So you've now removed the pot, removed rockwool (if necessary), split the plant and trimmed the roots, all you need to do is plant into your substrate. You need to make sure you give your plants room to grow so for smaller plants give them at least 30mm between each plant. With larger plants, realise that they will grow a lot more and spread out so bare this in mind. Stem plants you can plant fairly close together but bare in mind if insufficient light makes it down to the bottom, then the leaves will fall off and you'll be left with strange looking plants. Push your plants about 50mm into the substrate and I recommend using tweesers for this - it makes the job so much tidier.
7) Now your plants are in place, let them settle in. Try and avoid moving them and certainly don't trim them for at least 2 weeks. They need to become acclimatised to their new world - which may be dramatically different to their old one. It's your job to make sure you give them what they need, and in most cases that's lots of CO2, lots of fertilisers and plenty of water changes.
Any questions? Ask away :)