FALL PLANTING FOR HERBS
Charles Martin
NMSU Sustainable Agriculture Science Center

Fall is a time when most people think about putting away their tools for the season and enjoying the last days of balmy weather before winter sets in. But fall is also a good time for planting some herbs to get a jump on next season’s growth.

A number of herbs actually do better when planted in the fall. Lavender is a good example. Here at Alcalde we compared the survival and yield of fall-planting to spring-planting for two lavender varieties, English lavender (angustifolia) and Grosso (a lavandin type). We found that the fall planted lavender grew more quickly and produced a marketable yield of blooms the following season, while the spring-planted lavender needed an entire season to catch up before it even flowered. By the second season, spring-planted lavender had caught up in size, but the cumulative yields remained lower.

The reason fall planting works so well for some species is because of the physiology of perennial plants. It is the natural tendency of perennials to start to take energy from its leaves and send it down to the roots for storage in the fall. Shorter days and cooler nights signal the plant to begin this process. By putting more food and energy into their roots rather than top growth, the plants develop a larger and more vigorous root system for the following year. Since days are also shorter and cooler in the fall, transplanting many herbs this time of year is less stressful and uses less water than during the hot windy spring days that we have here in New Mexico.

Lavender can be transplanted while they are still green and growing, but most woody shrubs and trees do best when they are transplanted completely dormant. Even so, many gardeners cannot wait until late fall when woody plants have lost their leaves to begin planting. That’s okay, it is fine to go ahead and plant woody shrubs and trees in the early fall with their leaves still on, as long as the plant has developed leaf buds for next year. After transplanting, the shrub or tree will prematurely drop its leaves, but as long as next year’s leaf buds have formed, the plant should survive transplanting with a minimum of shock or dieback.

Completely dormant woody plants can be transplanted as balled or bare-rooted stock, but partially dormant or living plants must be planted with their root ball intact to minimize root damage and to maintain water uptake. Of course, any plant that is still green and active needs to be watered thoroughly after transplanting. This goes for so-called drought tolerant plants as well. Many people assume drought-tolerant plants do not need as much water, so they do not water their plants after transplanting. Keep in mind, all actively living plants experience some root damage and interruption of water uptake, and this is true for low-water use plants as well.

Fall is an excellent time to propagate many herbaceous species as well. Woody shrubs and trees cannot be propagated by root division or cutting the root ball because doing so would be exposing inner tissue to infection and rot. Most woody plants have not evolved to be propagated in this way. However, many herbaceous species do very well by propagation from root division. If you think about how many of these species evolved in the wild, growing in clumps in disturbed sites, being clawed at or dug up by animals for their nutritious underground parts, it is easy to understand why they tolerate and even thrive on having their roots torn up and spread around.

Have you ever noticed how overcrowded clumps of some herbs do so much better after they have been dug up, thinned out, and replanted into freshly dug, loose, composted soil? Many times you are actually doing the plant a favor by digging it up and removing competing smaller parts of the plant. It gives more room for the remaining plants to grow.

Like woody plants, herbaceous species do best when completely dormant. Ideally, wait until after a hard frost kills off the top growth and the leaves and stems are completely dry. This not only makes the dead top growth easier to remove, it allows an abscision layer to form between the stems and the dormant crown. This abscission layer is the plant’s own way of creating a neat separation layer between dead plant material and the remaining live tissue. But again, not everyone wants to wait until Thanksgiving to begin! If this is the case, cut back as much of the green top growth as possible before digging up the plant, being careful not to cut into the crown tips. Then the root ball can be dug up and split with a sharp flat shovel, a sturdy knife, or simply by breaking apart the crown with your hands. Some plants have evolved breaking points within the crown or along the rhizome specifically for the purpose of allowing dispersal of the plant in this way while minimizing possible infection points. If the plant is still active, try to keep as much soil around the roots as possible. If the plant is dormant, this is less critical, but still keeps the crown from drying out. Transplanted crowns will need only enough water to keep their roots and root ball moist.

Finally, fall is the preferred time for planting seeds that require chilling or a cold stratification period. Echinacea, or purple coneflower, is an excellent example of an herb that grows best when it undergoes a chilling period. It needs a minimum of thirty days of cold moist stratification in order for the seed to break dormancy. Don’t make the mistake of planting too early in the fall, because an exceptionally warm spell late in the season may cause stratified seed to germinate prematurely. I recommend waiting until after a killing frost, usually mid- to late October.

Even if seeds do not have a chilling requirement, I find fall planting of many types of herb seeds do better when planted in the fall. Small seeded species like mints, chamomile, or feverfew can be scattered on the surface of a rough seedbed, and the gradual freezing and thawing of the soil surface over the winter creates small cracks in the soil for the seed to fall into, providing naturally optimum soil conditions and planting depth for the tiny seeds, which no amount of manual seedbed preparation in the spring can seem to achieve. We have had best results with chamomile started this way. All of these fall planting tips teach us the value of learning from nature and ‘going with the flow’ of the seasons. If we do, we can appreciate each season for what it has to offer.

Reprinted with permission from Yerbas del Encanto, the newsletter of the Sangre de Cristo Unit, Herb Society of America, vol. 7, issue 8.