Savvy Moves for Fall Planting

One of the key ingredients to fall-planting success is the temperature of the soil. And that's just for starters.

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Filed under: Fall, Garden Zones, Plants

Fall Planting

Unless you live in an area where winter comes early, fall is the perfect time to plant trees, shrubs and a number of perennials. Foliage production has slowed, and the increasingly cooler temperatures drive the energy below into developing root systems.

It's important to determine the proper planting time. Plants need plenty of time to develop a vigorous root system before winter sets in and threatens their health.

Thanks to research done by researchers at Cornell University, determining the planting date is relatively easy to do. The researchers planted a variety of perennials and woody plants in Long Island, NY, on the 21st of August, September, October and November. For two consecutive years they evaluated the health of those plants and discovered that only the plants planted in late November showed signs of serious winter injury.

One of the keys to fall planting success is soil temperature: at least four weeks above 40 degrees F.

The real key to success was in the soil temperature at a depth of six inches. When the soil temperature falls below 40 degrees F, root growth comes to a screeching halt. The researchers further concluded that the last safe planting date is roughly four weeks before the soil temperature drops to 40 degrees F. In other words, plants need to be installed at least a month before freezing temperatures arrive in order to develop a life-sustaining root system.

Armed with this knowledge, you can determine the last safe planting date in your area by first finding the average first freeze date. (This information can be found in various gardening references as well as local weather forecasters and meteorologists.) Then count back four weeks, and you've got your last safe planting date.

The researchers found that soil moisture was also extremely important in establishing plants before winter. This is especially the case with evergreens. They discovered that a minimum of 4-1/2 inches of rain or supplemental irrigation was essential in keeping plants from drying out, or desiccating. Therefore, it is vital that you take care of fall planting at least four weeks before the first hard freeze, and be sure to keep those newly planted plants sufficiently watered.

Pushing Zones

You can also try growing plants that are rated at least one zone south of your USDA hardiness zone, James suggests. "It's something I encourage all you more experienced gardeners to experiment with because it can open up a whole new range of plant possibilities for your landscape."

There are two basic rules to keep in mind.

First, buy the largest-sized (and healthiest) plants you can find. "Most of the time I suggest gardeners buy small plants because they tend to suffer a lot less from transplant shock. And I, for one, like to watch plants as they grow to maturity," says James. However, in this case, James says it's actually better to buy larger plants because they more easily develop cold and heat hardiness. You can still watch them grow, albeit at a slightly slower pace.

Second, buy your plants from a grower who has grown them no more than one zone south of your own. These plants have been raised in a climate that is only slightly warmer than your own. This means they'll have a decent chance of surviving all but the worst winters in your location.

Carefully consider site locations when planting. Pavement and a protective wall provide added winter protection in these microclimates.

The best planting sites for marginally hardy plants in your garden include northern and eastern exposures with a wall to the south, and areas where plants can benefit from warmth released by paved areas. Areas to avoid include open, eastern exposures. Here, as the sun rises, it can thaw frozen plant cells too quickly and cause considerable tissue damage. You should also avoid low-lying areas where cold air has a tendency to rush in and settle.

Shaking Plants

Manipulating plant growth is something gardeners often do by pruning. "But I'm not talking pruning here," says James. "I'm talking shaking." If you've ever hiked up a tall mountain or even been on an open plain where the winds are fierce, you may have noticed that the plants growing in those areas are somewhat stunted. That's because the wind causes the plants to secrete a hormone that makes them grow shorter and stockier.

By shaking your plants on a regular basis, you may reduce their overall size. In fact, researchers found that by shaking a tomato plant for 30 seconds twice a day, its height was reduced by half in just one month. So if you have a plant that you don't want to grow tall, you can dwarf it just by shaking it.

The strong breeze of a fan creates the wind movement good for dwarfing houseplants.

In the case of houseplants, you can create windy conditions with a fan. Simply direct a fan toward the plants for just a few minutes several times a day, and they'll be stockier. And, by the way, you can also dwarf houseplants by watering them with cold water. Cold water slows down the root growth of plants, which in turn slows down the top growth.