Mt Cuba Center
Mt Cuba Center
Back to News Learnings – March 25, 2022


Mountain-mint Seed Cleaning

By Ellen Lake, James Rockwell, Amy Highland, and Sam Hoadley

Mt. Cuba Center collects plant material from wild populations for a variety of horticultural and conservation purposes, including evaluations in the Trial Garden. Collections from wild populations are conducted following ethical and sustainable practices. For example, Mt. Cuba’s team almost always collects seeds, not whole plants. This lessens any disturbance to the site and ensures that the plants can persist at that location, providing ecosystem services such as food for herbivores and pollinators.

Seed blower machine

The collected seeds are cleaned in preparation for storage or planting. Yes, sometimes seeds need to be cleaned. When seeds are collected, they include “chaff” – the dry, protective coating on the seed, as well as other natural debris. Chaff and debris may rot and spread pathogens when these seeds are sown or stored, particularly if conditions are too wet.

A variety of techniques can be used to clean the collected seeds. Here, we use a seed blower machine to separate viable seeds from chaff and debris. The viable seeds can be seen spinning in the bottom of the tube while the air current carries the lighter chaff and debris into collection points higher up the tube. This process can also help to sort out unviable seeds, which do not contain embryos, and thus weigh less than viable seeds. You can see in the photo how much chaff and debris (left) were separated from the viable seed (right).

Chaff and debris (left) and viable seeds (right)

Cleaning seeds also makes it easier for us to count and sow the seed, and to calculate germination percentages. Knowing what percentage of seed germinates helps horticulturists to plan how much to sow to ensure enough plants are produced for the gardens and research projects. Studying germination rates in the greenhouse also provides insight into what is happening in the field and the health of wild populations.

A purple-white flower of Pycnanthemum plant.

The seeds featured here are from Pycnanthemum virginianum, Virginia mountain-mint, which will be included in upcoming evaluation of the genus in the Trial Garden. Amy Highland, Mt. Cuba’s director of collections and conservation lead, sourced these seeds from plants in Pennsylvania. While some mountain-mint species are commercially available, Mt. Cuba aims to include wild genetics of locally occurring species in our trials as well as species that are currently not represented in horticulture.

Pycnanthemum can be found in mountainous regions, but the name “mountain-mint” is a misnomer. This plant grows in many conditions in the Eastern United States. Our native mountain-mints are similar in scent and a distant cousin of European mint but are distinguished by their blue green leaves and white flowers that have a hint of lavender. Mountain-mints are pollinator magnets in a league of their own! Frequent visitors include small butterflies and many species of bees and wasps.

For more information on mountain-mints and seed collection check out our upcoming class Ecological Explorations: Pycnanthemum on July 14th taught by Amy Highland.