Kathleen Hennessy has been writing about gardening for more than 15 years. Over the years, she’s been lucky enough to tour several wonderful nurseries, witnessing the care and skill each step of the growing process requires. Follow her on Twitter @29mingardener

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Plants to Market
by Kathleen Hennessy       #Propagation

Japanese maple (Acer palmatum) tree seeds are sorted for size and other factors before being selected for the sowing process.


As you walk through your local garden center, have you ever wondered where the plants come from? Why are there so many of one plant and only a few of another? The process of creating enough plants for us to purchase takes a scientific approach, technical skill, and a lot of artistry.

Every home gardener wants to have the latest and greatest new plant. That’s why nurseries work with breeders around the world to find interesting new varieties. Once they find those plants, they’re tested for several years to make sure they perform well and can handle temperature extremes. After testing, the work of creating enough inventory to sell to gardeners begins.

The process of creating plant inventory is called plant propagation. Top nurseries here in the U.S. use several types of propagation methods to multiply plants creating large enough inventories of each particular plant variety.


Plants grown in seed beds are evaluated for size, uniformity, and other characteristics.


Seed Propagation
Seed propagation may be the most familiar to home gardeners. Nurseries start plants from seed, just like we would at home, only on a much larger scale. This is the most common way nurseries grow annuals and some perennials.

At Monrovia Nursery, growers start all of their Japanese maple rootstock (Acer palmatum) from seed. Total production time for these beautiful trees can take six years or more. First, seedlings are planted and transferred into bigger pots as they grow. This process takes a little longer than a year.

The next step is to graft the seedlings. “For Japanese maples, you can’t produce a cultivar from a cutting,” said Ron Kinney, conifer and tree grower manager at Monrovia. So, cuttings of preferred Japanese maple varieties are grafted on to seedling rootstock. At Monrovia’s facility, the grafting process takes about eight months. The grafted trees spend time in a greenhouse, eventually being moved outside to a container field.

Each tree spends a few years in the field, where it is maintained and shaped. The trees are transferred to bigger pots as they grow. When they reach the desired size, they are shipped out to a garden center.


Cuttings grown in a sandy mix have developed roots and are beginning to grow, ready to be transplanted to the next growing media.

 

Cuttings or tissue cultures of shrubs, trees, or perennials are placed in cells with growing media to develop roots.

Rooted Cuttings
Creating new plants from vegetative cuttings involves taking parts of an existing mature plant called the mother plant. Propagation managers’ work with inventory managers to determine the number of plants needed. Often times, they’re estimating the number of plants garden centers will need three to five years down the line.

Propagation teams cut the stems or branches from the mother plant, then the cuttings are placed in rooting hormones to boost root growth. Stems can be placed in sand or another growing medium that makes it easy for the roots to grow quickly. Once the cutting reaches a certain growth stage, it can be transferred into a pot.

Spring Meadow Nursery, based in Grand Haven, Michigan, provides starter plants, called liners, to nurseries around the country for them to grow on to retail size. “The length of the vegetative propagation process depends on the variety and the time of year,” said Stacey Hirvela, horticulture marketing specialist at Spring Meadow. “Some plants will root very quickly while others take a long time. And some plants will root quickly at one time of the year and more slowly during others.

”At Spring Meadow, the cuttings go right into soil. “The cuttings are brought into our sticking room where a crew will place them into cells or pots,” said Hirvela. “As they pot them up, the trays slide down the line and get watered, which settles the soil around the stem and starts signaling to the plant that conditions are right for root formation.”

At Bailey Nurseries’ facilities, cuttings also go into liners, but some cuttings spend time in sterilized sand. The cuttings are placed in the sandy growing medium in a greenhouse. The sand is a very porous, allowing for good drainage, yet still holds up well under the consistently misting conditions the new cuttings require.

Once optimal root growth is attained, the plants can go into a garden bed, larger liner or a container. They’ll spend time in a greenhouse, out in a container field or split both locations. Here they are watered, fertilized and trimmed to reach their best growth potential. They can also be repotted in larger containers as they grow. It can take two years or longer for the rooted cuttings to reach the size and quality needed for the plant to be sold at a garden center.


Tissue culture involves taking tiny pieces of plants for propagation. The pieces develop into the exact same plant as the one from which the cuttings were taken.


Tissue Culture
A third propagation method is called tissue culture. Stepping into the tissue culture lab at Monrovia Nurseries facility is a very futuristic experience. Every part of the lab is sterile and each technician has a very specific and intricate job. With tissue culture, new plants are created from an original plant using very small cuttings. Technicians separate tiny parts of the plant, then transfer those parts into a growing medium in a sterile container, such as a test tube or glass jar. This method allows nurseries to create several offspring from one parent plant. Each of the new plants is an exact replica of the parent plant, almost like a clone.

Nurseries use tissue culture for a number of different reasons. If enough root stock is not available, tissue culture provides an alternative for propagation. For some varieties, it can be a faster way to create more plants. Creating new plants from tissue culture also protects the availability of varieties. “If we were to have an issue in the nursery, say a particular pest or disease, that wiped out all of the root stock of one type of plant, having a stock of that plant in tissue culture means that plant would not be lost,” said Sam Huang, a craftsman at Monrovia.


‘Great Expectations’ hosta (H. ‘Great Expectations’) is propagated by tissue culture and grown in glass jars until ready to transplant into cells, or other potting media.
 

As the new plants created from tissue culture grow, they can be transferred to larger containers within the lab and eventually may become plugs – small plants placed into soil. These plugs are brought into the greenhouse to continue the growing process, and eventually are planted into containers and grown in the field.

All three nurseries ship plants to garden centers across the country, providing much of the inventory gardeners purchase. Growing plants to sell to home gardeners is not at all like producing other products. Plants are living things that are affected by weather, water, disease, and many other influences that typically wouldn’t have an impact on other types of consumer products.

Next time you’re browsing through a garden center, take a moment to appreciate the time, talent and artistry these craftsman provide to bring us each wonderful new plant.


Cuttings or tissue cultures are placed in plugs, held in trays until they reach a size where they can be planted into a pot or larger tray. Then, they are shipped to nurseries, greenhouses, or garden centers to finish off, sometimes called growing on, until they are retail ready.

 

A version of this article appeared in a May/June 2017 print edition of State-by-State Gardening.
Photography courtesy of Kathleen Hennessy, Proven Winners/Colorchoice Flowering Shrubs, and Bailey Nurseries.

 

 

Posted: 05/09/17   RSS | Print

 

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