Growing is quite simple depending upon your locale.
For the poster asking about the possibility of growing in the tropics... It is quite possible to grow in tropical environments if one utilises the proper variety and compensates for the heavy precipitation depending upon the season. The variety is super-important because after rosetting the plant needs longer nights for proper morphine formation. Usually people grow in the tropics, have fabulous results but when they harvest they net terrible yields with very poor morphine content.
Ideally you want granular soil with at least 70% moisture content and a pH of 6.5 to 7.5. For fertiliser, I will give the commercial values and any interested parties can do the math to adjust the numbers since I am pretty sure that noone here is considering planting at least a hectare.
Per hectare, prior to sowing, fully till 30 tonnes of manure topped with 90 kilos of granulated phosphate. The only other fertiliser will be applied at rosetting. At that point spread a double stratum of nitrogen and potash at a ratio of 105:70 kgs per hectare (for every hectare lay 105 kg of nitrogen, 70 of potash). This will boost your opium harvest by 30% so it is well worth the effort.
You need 3 kilos of seed per hectare. First, coat your seed with mercuran and then mix the seed with 3 kg of fine sand. Usually commercial growers till in rows 72 cm apart to leave room for irrigation machinery but in my case I broadcast seed (though it makes for a lot more expence to have labourers thin by hand square meter by meter). The mecuran will protect your seedlings from common disease, etc and the sand helps it to broadcast evenly, especially if there is any wind about.
From the point of sowing you just need to retain that minimal moisture content of 70% but when the spout they have to be watched. At their 2nd set of true leaves (plants have "baby leaves" much as humans have "baby teeth) they need to be thinned to 160K per hectare. Their 2nd (their last) thinning takes place after their 5th set of true leaves has fully opened and you want a final density of 110K per hectare.
From that 2nd thinning you just wait for rosetting to spread that nitrogen and potash and then cut back your irrigation for a moisture content of 50%. If yoy have above 50% at this point you leech out whatever morphine has been produced and stem formation of new morphine.
When your pods naturally drop their last leaves you need to wait 1 week and then begin walking your field(s) to observe their appearance. Each pod has a corona (crown) sitting atop it. As the plant grows the corona lays flat but between 7 and aeaw days AFTER that last petal drops the corone will become erect. At the same time there will be a change in colour to a bluish-green, and above the stem on the bottom of the actual pod there will be a faint beige ring that is only visible to the naked eye. When those 3 attributes are present the pod is at technical ripeness and needs to be lanced. If you wait just 48 hours you lose nearly 10% of your morphine. Wait 84 hours (1 week) and you lode 30% and it continues to decrease literally by the hour.
Generally you get 3 decent harvests off of each pod, with each lancing 48 hours apart. A lot of people believe its best to cut laye in the day but they are actually wrong. Optimally you want to lance betwen 12PM and 6PM. Then, brgin harvesting (collecting) at 5AM. 1 adult can handle 1/5th of a hectare per day so plan accordingly.
A poster said that commercial growers let the plant dry before harvesting. That is only true in Tasmania. Because of labour costs related to both their huge crops as well as Tasmania's isolated location it doesn't pay to manually harvest. There is also the additional factor of the Tasmanian Co-op aiming for thebaine and codeine (as opposed to morphine). If you aren't trying to net morphine manually harvesting is counter-productive. Letting the plants dry on the stock simplifies mechanical harvesting. They then do a whole-plant extraction very similar to the Kabay Process (aka Hungarian Method).
Their yields are a lot lower that way but because it gains cost-effectiveness in terms of labour it is well worth it. I have to add that they make a pretty penny by aiming for alkaloids other than morphine. Usually, codeine isn't obtained naturally. They methylate morphine to net codeine which drives the price of the alkaloud up. Whole-plant extraction bypasses the conversion. Thebaine is only present in miniscule concentrations and so utilising traditional methods don't render its production especially lucrative. Aside from whole-plant extraction the Co-op has a trademarked variety (actually 3) that have only negligible morphine content but do have astronomically high thebaine concentrations.
For the poster who said Persian White poppies have the highest morphine content, no, not true. It isn't even a variety per se. It is a marketing gimmick like companies that label Kratom as "Bali," etc. In reality the label means nothing.
The highest concentration, on average (as well as highest ever recorded) was a variety named "ZL29499," produced in the former Yugoslavia in a university programme. While the average in all varieties hovers around the 10th percentile, this variety topped out at 28%. Iranian and Afghan varieties are low producers.