Grower 101: Bare Root Perennials
Bare root perennials are dormant plants with the soilremoved from the roots. They are typically field grown for a period of time,usually one year, and harvested. Once the plants are dug, the tops are trimmeddown to approximately 1 inch from the crown with the exception of evergreenperennials such as iberis, lavender, dianthus, Phlox subulata and yucca. Thesebare root plants are then shipped to finish growers or end users.
Root Systems and Plant Grades
Bare root perennials display four different types of rootsystems. Fibrous roots are composed of profusely branched roots with many siderootlets. Taproot is the main descending root of a plant. Taproot perennialsprefer cool temperatures and dry soil conditions once planted in containers. Iftemperatures are too warm, they put their energy into top growth and don’testablish a satisfactory root system. A Fibrous root system often has no mainor taproot development and, as a result, can be divided for a greater return oninvestment. A rhizome root system is a specialized slender or swollen stem withbranching close to the soil surface. This type of root system produces roots, stems,leaves and flowers along its length and apex. The fourth type of root system isthe Crom, an underground, bulb-like portion of the stem of a plant thatconsists of fleshy tissues.
Bare root perennials are available in different grades. Eachgrade is representative of the number of branches/blooms per plant and thefinish size of the plant. Plants such as astilbe are graded by the number of”eyes” per plant. Plants with 1-2 eye divisions are suitable for2-quart to 1-gal. containers. A 2-3 eye division is suitable for a 1-gal.container. Plants such as hemerocallis are graded by the number of”fans” per division. A 1-2 fan division is a “heavy” plantgrade with high blooming potential.
Ordering and Receiving
When ordering bare root plants it is important to keep inmind that they require prompt planting upon arrival. For spring greenhouseproduction, schedule your order to allow 6-8 weeks of growing time in a coolgreenhouse 48-55º F. If grown outdoors, arrival should be scheduled whenweather conditions are suitable for transplanting. Outside plants should bekept above freezing and protected from excess rain. Most bare roots plants,with few exceptions, should be kept on the dry side until they break dormancy.
Once your plants arrive, you should transplant all rootswithin 1-2 days of arrival and make sure you label them for correctidentification. Because some varieties are stored in freezers, if you find thatsome roots are still frozen, thaw them slowly in a cool room before handling.If you find that your plants are dry, soak the roots in water for one hourbefore planting. Soaking will help establish plants faster. However, if youcannot transplant immediately, store plants in loosely closed plastic bags in acool area 35-40º F for no longer than 2-3 days.
Upon arrival, you can check the condition of your bare rootperennials by inspecting their appearance. Roots should be firm, relatively dryand light brown in color. Since most plants have been packed in advance forcold storage, appearance of light surface mold is not unusual. This is causedby the high humidity necessary in cold storage and is not harmful to theplants. It is not necessary to do any preventative fungicide treatment; surfacemold will disappear quickly if you provide good air circulation.
Some perennials require priority treatment after arrival.Evergreen plants can desiccate more quickly if left exposed, therefore begintransplanting your evergreen plants first. Once these are potted, proceed tocontainerize other bare root plants, and finish with the items in pots.
Planting and Growing
When planting, most perennials should be potted with theircrown approximately 1-inch below the soil surface. Sometimes, plants benefitfrom fanning or spreading their roots when transplanting. This will encouragenew root growth. If the roots are too long, they can be trimmed. (Contact yoursupplier for correct techniques on trimming.)
Walters Gardens suggests using a commercial, bark-based,soil-less mix. For perennials, look for a media with total porosity of 50-60percent, which maintains 20- to 25-percent porosity after irrigation. It isimportant to establish a balance between water-holding capacity and aerationfor optimum plant growth. The media pH should be between 5.5 and 6.2, and the pHof the irrigation water should be 5.4-7.0.
Once roots are planted, water thoroughly as this helps toeliminate air pockets. Low soil temperatures that keep the plants too cool andwet for a prolonged period of time should be avoided. Morning watering is bestfor perennials because it gives the foliage a chance to dry out before theevening hours; this will help reduce diseases. The growing surface you selectshould have good drainage.
Temperature is a key factor when growing bare rootperennials. For spring planting, keep all plants above freezing. Cold and wetconditions may cause plants to decline or rot. For best results, keep plants at48-55º F for 10-14 days after potting to promote root growth, and thengrow at 55-60º F until finished. Another important factor is light. Mostperennial varieties should be in full sun, although there are some shade-lovingplants.
When fertilizing, to prevent salt build-ups, avoid using anyslow-release fertilizers in the soil mix until it starts getting warmer (aroundApril 1st in the North), because very little fertilizer is released when it iscool and cloudy. (Follow the manufacturer’s recommendations.) This could resultin severe dieback or death if the plants are exposed to freezing conditions. Inaddition, newly planted perennials are not able to absorb fertilizers as theyare establishing their feeder roots. Wait to fertilize until there is 4-6inches of growth. For actively growing perennials, liquid fertilization is oneoption; however, growers have to ensure that appropriate levels of nutrientsare maintained in the growing medium. A solution containing 100 ppm nitrogenfrom an NPK fertilizer, such as a 20-10-20, at every watering will besufficient in most cases for 1-gal. containers.
As perennials mature, you might want to consider spacingplants to provide good air circulation. Some growers refer to this as”checker-boarding.” Pruning is also very important, as it will keepyour crop compact, encourage crown and root growth and allow water to penetratemore easily. Pinching and pruning perennials in their containers will not onlykeep plants attractive looking, but it will also encourage rebloom.