Timing of the Harvest
After 5 growing seasons in the field, Rhodiola rosea should be ready to harvest. Five years is usually sufficient time for the roots to mature and generate concentrations of rosavins and salidroside which will meet the criteria of customers. Before the crop is harvested, root samples should be dug and sent for HPLC (high performance liquid chromatography) analysis. The USP method is the current analytical method which is accepted worldwide.
Five growing seasons should also provide acceptable root yields in terms of weight to be economic for the grower. In Alberta, several strains of Rhodiola rosea has shown excellent to fair yields. The search for the best strains in terms of yield and bioactives is ongoing. Average size of fresh roots per plant can very from .3 to greater than 8 kg. Less than .3 kg per plant on average would not be considered economic to harvest.
Root yields typically increase each year, with substantial growth in the early part of each season. Much of the increase in root mass occurs in June and early July in Alberta. Root yields increase dramatically after the second year in the field. Bioactive content also increases each year.
Rosavin levels will spike towards the end of September and early October. This is the best time to harvest Rhodiola rosea. The root at this time of year will have gone dormant. Most shoots have dried and can be mowed off, if possible.
It is best to harvest when soil is relatively dry. If soil is wet, it will compact around the plants, often tearing off roots and making mudballs which are hard to clean and process.
Before you harvest, always have a plan for what you want to do with the freshly dug roots. If you are interested in selling your roots to Rhodiola Growers of Canada, please contact Nelda Radford at 403-650-7257 preferably one year in advance of your harvest. This gives us time to find a buyer for your crop. Please refer to the “Who are We” article to find out more about contracting your harvest with us.
If you are using Plastic Mulch . . .
Prior to harvesting, plastic mulch should be removed from the rows. A mulch roller can be used to collect plastic mulch in the mulch is not embedded with weeds and dirt. Most mulch rollers are designed to be used to take up mulch after one growing season. After five years, it is much more difficult to take up the mulch with a roller.
In some cases the best time to remove the plastic is before any growth occurs in spring. In other cases the plastic has been covered with dirt and weeds and cannot be separated from the Rhodiola prior to harvest. If the plastic mulch cannot be removed, the cleanup after harvest can be extensive. In addition, some portion of the Rhodiola rosea will remain in the plastic and can be removed during cleanup.
Types of Harvesting Equipment
There are different types of harvesters or diggers. Rhodiola harvesters at a minimum should loosen the soil and elevate the roots onto the surface of the soil. Rhodiola roots are typically shallow (within the top 6 inches of the soil surface) and they easily loosen from most soils, as long as the soil is not infested with perennial weeds. With some harvesters the soil can be separated from the roots and the roots windrowed or conveyed into a container.
If there are less than 1000 roots, the best method to harvest may be by fork or shovel. The person digging should be aware that the roots of Rhodiola rosea grow horizontally more so than vertically. Care should be taken to harvest as much of the lateral root as possible.
Harvesters and Diggers
There are two main types of soil loosening devices or harvesters/diggers suitable for Rhodiola. The first type is often referred to as a potato digger. The digger consists of a wide horizontal blade to excavate the soil and roots. This type is used when the Rhodiola is grown in beds or multiple rows. Make sure that the horizontal blade is wide enough to dig the entire width of your rows.
Tines or screens usually follow the blade to separate the roots and soil. A PTO driven vibrator or shaker can also be used to assist the blade in excavation and separation of the soil. Some diggers have open link conveyors or tines to separate and lift the roots. Spacing of the links or tines is critical to convey the plants and separate the soil. Spacing depends on the size of the roots harvested.
Another method is to use two converging disks to loosen and lift the roots onto a conveyor. Make sure that the disks are set wide enough apart to harvest the entire width of your row. Often these diggers are meant for narrow rows of sugar beets or carrots.
A potato harvester can also be used for larger fields. This type of implement will separate the soil and lift the root onto a platform where workers can load the plants into bags.
Word of caution: All types of machines are designed primarily for annual crops. All implements will be put under more stress with a crop that has been grown for five years, as the soil has settled and compacted during this time. Make sure to use machinery that will hold up to the greater stress of compacted soil.
Other types of harvesting equipment
If soil is loose, weeds are limited, and plastic is removed the following equipment could also be considered for harvesting Rhodiola:
Rock bucket – attached to the front-end of a tractor or skid steer. The rock bucket is shaken and the loose dirt will fall out, leaving roots in the bucket which can be dumped into a holding bag.
Spinner bucket – this is an attachment for a skid steer. Similar to the rock bucket, the cylinder of the spinner bucket is pushed into the row to collect both root and dirt. As the cylinder spins, the dirt falls out and the roots can be dumped and collected.
Collecting the freshly dug Rhodiola
Once the Rhodiola rosea roots are dug and exposed to air and the environment, it is essential to protect them. Roots should be collected and placed into clean large bags or bins with ample ventilation. The bags/bins should be kept in a cool shaded area with good air flow. Bags should not be closed up until ready for transport. Exposure to heat and the sun will accelerate decomposition of the roots. Limited air flow will invite mold growth. Heavy bags will compress roots under excessive pressure, causing mold growth and decomposition from crushed roots.
