I've grown Amorphophallus titanum for a number of years. Here's some information on how I grow them.
Media: I like to use a mix of Orchiata orchid bark, medium size (Power size), Pro Mix BX with microrhizzae, and coarse #3 Perlite or Sponge Rok.
Pots and Media: I use platic pots, The pot should be large enough so the corm can grow. I usually leave about 4-6" on each side of the corm. So a 12" corm will need at least 20 to 24" pot. For large corms in 50 gallon or larger pots or tubs, I use 2 parts bark, 1 part Pro Mix and 1 part Perlite. I incorporate 1 cup of AG 65 Dolomite lime to this mix. Under my conditions, this mix will last at least 3 years. For smaller pots, I use a mix of 1 part bark, 1 part Perlite and one part Pro Mix. I incorporate Dolomite at about 1/4 cup per 20 gallons of mix. This mix lasts 1-2, sometimes 3 years.
Potting: Repotting is best done during the dormant season. Repotting when it is initiating growth is difficult as you must not damage the emerging shoot or roots or wound the corm which is very heavy. I have heard of plants dying when the new growth is broken off, but I've never done so. I've also heard of corms rotting then it is wounded. I've grown them after they've gotten a small wound with no problem aside from keeping it relatively dry for a month or so. So it is much easier to just repot when it is dormant, keeping it barely moist until growth initiates. I have heard that many growers remove the corms from the pot and media and store them dry, but I've never done this.
To pot, I spread a 6" layer of media at the bottom of the pot. The corm is placed with the" hole" on the top. This "hole" is where the old growth was and the new growth will emerge from. The bottom of the corm has a hard "bump" which is the remnants of the old corm. Additional media is added, firmly tamping down every 6" or so till the top of the corm is covered by about 6-9" of media. As the growth emerges (a single leaf that looks like a small tree called a pinnate leaf) the roots will emerge simultaneously from the top of the corm at the base of the leaf. Very few if any roots will form from the sides or bottom of the corm.
New leaves emerge and are very acutely pointed. Flower buds are pointed, but less so. The difference is very slight and not exact.
Feeding: Once growth initiates and breaks the surface of the media, I fertilize with a mix of 1 cup Nutricote Type 360 and 1 cup Grow Power (coarse 8-8-8.) New Grow Power (1 cup) and Dolomite lime (1/2 cup) is added every 3 months.
In addition to solid food, I fertilize weekly with Peter's Excel 15-5-15 Cal Mag (2 teaspoon per gallon of water) and Superthrive (1/4 teaspoon per gallon of water) using a Siponex mixer. I flood the plants till the drain holes weep. Dyna Gro Pro Tekt (1/2 teaspoon per gallon of water) is added separately, about 10 gallons per large pot (50 gallon plus size.) You must apply the fertilizer and Pro Tekt separately as the Pro Tekt will cause the fertilizer to precipitate out of solution.
Watering: Once growth is initiated, I water daily, flooding the pot. After a few months, the media will often pull away from the sides of the pot because of the growing corm. I simply fill in these cracks with the standard media mix.
Growing: I've grown and flowered them in both shay and very bright conditions. Both work for me here in Hawaii. I think bright conditions (just short of scorching the leaves) produces the best growth. With bright light, good air circulation and frequent, heavy watering and feeding is a must.
Flowering: It will flower when it wants to, almost always in the late spring to late summer season. But this is not for certain. The more I find out about growing this species, the less "absolutes" there are about growing and flowering these. If you ever figure out how to make it flower, or predict when it will flower, let me know.
I no longer grow this species and have never sold it, so don't ask.