Please note: Live Plants cannot be shipped to Western Australia or Tasmania, due to quarantine restrictions. All other states are OK.
What do you need to grow plants?
Successful plant growth requires a balance of light, nutrients, trace elements, and carbon dioxide (CO2). The light should be provided in a spectrum the plants can absorb, must be of great enough intensity to keep the plant alive, and should be consistently on 10-14 hours a day. Most nutrients are supplied by fish waste. Some trace elements might be supplied by your tap water, but are more consistently obtained using commercial trace element mixtures. CO2 is supplied partly from the air and partly by your fish. If your plants have a deficiency of even one of these factors, their growth will be limited. (Don't panic about this; most of us don't need optimal plant growth.) Overabundance of one factor over another may cause problems, such as plant malnourishment, undue algae growth or toxic buildup.
What should I put in my substrate?
Gravel or sand is a good start! Size is an issue; with small grains the roots might not be able to get a good hold and the sand tends to compact, while larger gravel has a tendency to collect pockets of rotting detritus. Most believe the ideal size is 2-3mm gravel, while a few others like 1-2mm coarse sand (though it may be harder to find). The bottom 1/3 of the gravel can be supplemented with a fertilizer, of which popular choices are peat (softens water), laterite (a clay containing iron, usually used with undergravel heating systems), and soil. One word of warning: if you use an undergravel filter, it may suck your fertilizer back into the tank instead of keeping it with the bottom of the gravel.
How deep a substrate?
In general, it's good to match the substrate with the types of plant (or types of roots). For instance big Amazon Sword plants like deep gravel of 10cm, but Lilaeopsis grass can do fine with an inch or less. This can be helped by terracing the back of your tank to be deeper and planting your deep-rooted plants there. You also can't go wrong with a uniform 7cm of gravel all-around.
What kind of plants can I keep with fish X?
What kind of fish can I keep with plant X?
These are essentially the same question, though asking the second one shows you are a serious plant person. You need to match the habits of the fish with the plant. Big cichlids that like to dig should not be kept in a tank with rooted plants, though floating (or ephiphytic) plants are fine. Vegetarian fish should not be kept in a tank with plants they like to eat, unless the plants grow faster than they destroy them! Some algae-eating fish also turn out to be plant-eaters too. In general, try and learn the habits of your fish before you buy them and your plants, and be prepared to find out what works by several trials.
Some fish that can be kept with virtually any plants: small tetras, danios, rasboras, gouramis, discus, bettas, angelfish (Pterophylum), rainbowfish, Corydorus catfish, livebearers, killifish, dwarf cichlids, and in general most small fish.
Can you grow plants with an undergravel filter (UGF)?
Yes! Make sure you have enough gravel for the plants to be happily rooted. It should also work best with a very slow flow rate. Pluses of UGF may be an increased circulation to the roots. However, you will probably get roots growing in the plates, it will be harder to vacuum everything, and will be a major pain to pull and replant.
What temperature do I keep a planted tank?
This varies from plant-to-plant, but you can keep most aquatic plants from 22-27C.