Questions about Lemonbalm Production

I am working on a document for the Ministry of Agriculture of Quebec. It's a technical document about the field production of Lemonbalm.
My questions are:
Is the variety Quedlingburger the most interesting and the only one for commercial purpose you would recommand for mechanical harvesting? Is it the tallest available? Is it as hardy as Melissa officinalis? Are both zone 5?

Both Quedlingburger and Citronella are well suited for mechanical harvesting. They are taller and more aromatic than the standard variety that is commonly sold. The standard variety is a more compact variety better suited for pot plant culture.

In many regions in Quebec, the hardiness zone is 4, so in case there won't be much snow coverage some winter, I thought of recommending the possibility of using mulch (straw or Agrotextile). But it would cost so much and be so labour consuming.

Even in our area, zone 5, lemon balm does not always survive the winter especially when there is not much snow cover. Losses over winter can range from 0% to nearly 100%, but most winters we see close to 100% survival. Key to its success in our area is our sandy soil which allows water to drain away from the roots. If the soil is heavier, more like clay, then the survival rates will be lower.
In zone 4, mulch may be necessary. It really depends on how much risk the farmer is willing to assume. If the farmer can live with heavy losses every 3 or 4 years, then perhaps the cost of applying a mulch can be avoided. If the farmer is not willing to risk a crop loss then there is no choice but to apply the mulch. In that case, the eventual product should be targetted for a higher value niche market such as the fresh-cut, value-added or organic (biologic) markets. Trying to compete on the worldwide dried botanicals market with a costly mulching program will be difficult.
Another option is to treat lemon balm as a hardy annual: sowing or planting in the first summer for harvest the following summer. At the end of the second year, the field is plowed under. This option makes it easier to keep the fields clean of weeds.

Yield: is it safe to mention the yield the first year is about 20% of a normal yield (one)? The yield you mention – 5000 kg/ha – is that for the entire plant or only leaves? In the literature, about yields, I found no details mentioned about that important consideration and leaves only weigh much less than entire plants.

The five tonnes per hectare figure is an average of several sources that give ranges from 2000 kg/ha to 6800 kg/ha for dried whole herb, i.e., the whole above-ground parts of the plant, including the stems. The fresh weight yields range between 10 to 25 tonnes per hectare. For dried leaves only or for dried flowering tops, yields range from 1000 kg/ha to 1800 kg/ha.
In the first season, the farmer may or may not decide to make a cut. This depends on the local situation and how the crop grows. Because of the colder zone, it may be better not to cut any herb the first season so that the plants enter the first winter as strong as possible. If however, the plants reach the flowering stage early in the first season then a light cutting could be considered. In that case, it is unlikely that the yield will be more than 20% of the 5000 kg/ha figure we give.

Is it realistic to mention the second, third and fourth year would give constant yield, then decrease, so that one should renew the fifth year? (We are thinking of organic or biological culture.)

By the third year and especially by the fourth and fifth years some overwintering losses are likely. It becomes a management decision for the farmer to decide when it is better to plant a new crop for better yields.

Can you give me prices you obtain for your yields? Is it milled?, in ballots?

Prices in 2000 ranged from US$1.85 to $4.50 per pound depending on the amount and whether the product is certified organic. Higher prices were reported, so these prices should be regarded as minimums for summer 2000.