Should I bother cycling a planted tank before planting?

Tank cycling is important for a few reasons.

The main reason to let a planted tank mature (by doing a dark start) before planting is that it reduces chances for plant melting and also reduces incidences of algae in a new setup. Letting the tank gain some biological maturity before planting reduces algae triggers, and creates a better, more stable environment for sensitive plants & livestock

What differentiates a matured tank and make it so much more stable compared to a fresh setup is the microbial population that develops in a tank system over time. Microbes and decomposers break down and consume organic waste. A biologically matured system is one where there is enough microbial life to break down harmful organic pollutants quickly into benign substances. This creates a more favorable environment for both livestock and plants. The faster waste gets broken down, the less triggers there are for algae to spawn. Many microbes also consume algae directly. 

Diatoms and green dust algae are common in new setups; so common that many experienced folks think that it is an inevitable stage that all tanks have to pass through. However, both these algae stages are greatly minimized or absent if tank is allowed to pre-cycle and mature beforehand. Especially for beginners that have a hard time handling algae, avoiding the issue to start with is a smart move.

High levels of ammonia and/or nitrite can melt delicate plants (such as plants that come in tissue culture format) and is harmful to livestock. This is more significant for aquasoil tanks that use ammonia rich aquasoils, where initial ammonia levels can be significant. 

For tanks that use higher levels of light, its easy for plants in a new tank to be quickly smothered with algae if the biological environment is not matured.  

Ammonia is great as plant food ?

Ammonia is a great source of Nitrogen for plants; which generally use less energy to synthesise Nitrogen from ammonia than from say Nitrates. However, since ammonia is toxic, plants cannot store the compound directly n their tissue, and have to reduce the ammonia to Nitrate before it can be stored.

The downside of having ammonia in the water column is that it is toxic to both fish and plants (if your pH is elevated above 7). This is a key reason why delicate plants such as Utricularia graminifolia melt when planted freshly in new setups. The other hardy plant that melt in new setups often is Bucephalandra. Both these species are much better off in matured tanks.

Bucephalandra are undemanding plants, but require a stable, clean, well filtered environment to do well long term. This easy plant often melts in new setups.

Reduced toxicity of ammonia below pH 7?

In biological systems, ammonia can occur in two types - ionized form (NH4⁺) and as the unionized form (NH3). How much ammonia exists in one form or the other is largely dependent on the pH range of the aquarium. Ionized ammonium (NH4⁺) is much less toxic. Therefore, ammonia toxicity is reduced significantly in lower pH environments as most of the ammonia present will be in the ionized ammonium (NH4⁺) format. In aquasoil tanks where high levels of ammonia of emitted, one can escape most of the downsides of elevated ammonia due to the strong buffering capacity of the soil lowering the pH below 7.

Tank cycling The old way

​The old method of cycling a planted tank was to add a light fish load of hardy fish, which then produce organic waste and ammonia; the tank was then left to build up the bacteria naturally over time. This can take many weeks, as more and more livestock was added slowly. Seeding the tank with seasoned filter media or mulm from the substrate of a previous setup are additional ways to kick start the cycling process. Depending on how it's done, this process can be tough on livestock. In acidic tanks (pH <7), ammonia toxicity is alleviated as most of the ammonia is in the NH4+ (ammonium) format due to low pH environment.

Today's fish-less cycling with plants

Nowadays, fish-less cycling with plants is the rage. This involves adding liquid ammonia regularly into a new tank; fully setup except for livestock or plants, to grow the bacteria colonies. Follow these 3 steps:

1. A dose of 2ppm of ammonia is added, then the water is tested after a couple of days (takes about 3 days or so from a cold start to even see levels change). When ammonia levels start to decline, one would start seeing a build-up of nitrite. The first step of the ammonia oxidation cycle is started (but not necessarily completed).
2. Additional ammonia is then added every day to feed the bacteria (add enough to raise levels back to around 2ppm). After many more days, nitrite levels would fall, and one can then measure nitrate levels rising as the bacteria converting nitrite to nitrate has populated. This takes longer than step 1 as the bacteria responsible for nitrite conversion to nitrate populates more slowly.
3. Eventually, even with additions of ammonia, nitrites and ammonia would measure at 0 after a 6hr period, while nitrates accumulate. The ammonia cycling process for the tank is now complete. The entire process can take 4-6 weeks depending on tank parameters.

Typically, we would change 80% of tank water to reduce nitrates before adding livestock. Adding starter bacteria cultures at step 1 greatly speeds up the process. Bacteria products work, but many are sensitive to temperature. Depending on how it is transported and stored, cultures could be DOA (dead on arrrival). That is the main risk/downside with bacteria products.

Cycling with aquasoils:

1. If you do not use starter bacteria products, it is a good idea to add mulm or used filter media to kickstart the cycle. Without the use of starter bacteria products, full cycling of the tank can take up to a month or more. The lowered pH of the tank water due to the buffering capacity of aquasoil reduce ammonia toxicity as most of the ammonia exists as less toxic ammonium(NH4+) format in low pH (below 7). This allows hardy plants to be planted and grown even in early stages where ammonia levels are detectable. However, more sensitive plants, such as Utricularia gramminifolia, and tissue culture plants in general, should only be planted after the tank is cycled - they melt easily in fresh soil.
2. With the use of starter bacteria products, cycling time can be shortened to a week plus. After filling the tank, we recommend letting the tank soak for a couple of days without running the filter. On the second or third day, do a 100% water change then start running the filter. This removes organic debris, dust and sugars released from the woods and prevent the filter from taking up a lot of debris at the start. After starting the filter, dose the starter bacteria culture into the filter intake. We would increase the KH to 3dKH and add a few pieces of limestone (about 200 grams of Seiryu per 100 litres) temporarily to the tank to prevent tank water from becoming too acidic if the water is super soft.
3. Wait 4 days and take ammonia and nitrate readings. If there are nitrate readings, it means that the cycling has started. However, due to the tremendous amount of ammonia the aquasoil releases, chances are ammonia readings will still be high. Do a 90% water change and dose another dose of starter bacteria culture.
4. Wait a day and take ammonia/nitrate readings. If ammonia reads 0 and nitrates reading is positive, tank has cycled. However, if soil load is high, ammonia reading can still be positive as the soil releases a lot of ammonia, in that case, wait a couple of days and repeat step 3. Due to reduced ammonia toxicity below pH 7, which is what will generally happen in aquasoil tanks, planting of standard, non-delicate plants can happen as long as ammonia readings are low (below 0.5ppm or so). However, for sensitive livestock such as shrimps it is better to wait till the tank has fully cycled.

In the setup videos on youtube, folks seem to plant immediately in fresh aquasoil ?

The type of plants and aquasoil used matters a lot. More labile soils melt delicate plants easily. Hardier plants can be used in fresh setups without as much downside.

What you also do not see is the daily water changes, replacing of melted plants and cleaning of algae behind the scenes. Hardy species that are planted straight into fresh soil generally recover even if they take the initial hit from the uncycled tank. However, for many beginners that do not have good control of their CO2 and other growth parameters, it could result in losing entire batches of plants.