September Gardening

Shorter autumnal days and mild temperatures mean lower stress on new plants, and the inevitable rains help keep those new plants watered-in. That means less work for you (and maybe a few extra days leftover to enjoy the hammock).

Fall is also a great time to shop for hardy plants! We’re always stocking up on conifers, winter-blooming shrubs, and Pacific Northwest native plants this time of year. Fall favorites—like pansies, ornamental cabbages and kales, and overwintering vegetables and herbs—are all available in autumn.

Some plants are borderline hardy here and may be challenged by the extreme cold. Because of that, they should be planted in the spring, allowing their roots to develop before freezing temperatures arrive.

In Portland, it’s generally safe to plant anything that’s hardy to Zone 7 and below in autumn, but popular Zone 8 plants—like New Zealand flax (Phormium), star jasmine (Trachelospermum jasminoides), or hardy Gardenias—should wait until spring.

If you choose to install Zone 8 hardy plants in fall, you’ll need to develop a plan for protecting them during harsh winter weather events.

Some of your summer annuals may be a bit tired looking or overgrown. In some cases, a trim and a bit of water-soluble fertilizer will get you a few more weeks of bloom. Others should probably be discarded in favor of some new fall color (annuals and short-lived perennials that look amazing through autumn and often into winter). Pansies, kale, dusty miller, mums, asters, and black-eyed-Susan are just some of our favorite fall color annuals. There are plenty more flowers to enjoy; the growing season isn’t over yet!

As for perennials, late-season flowers are in full swing and fully stocked on our shelves—including asters, many daisy style plants, yarrow, and Salvia. Early to mid autumn is one of the best times for planting, assuming temperatures have cooled since summer. The majority of cold hardy perennials thrive with fall planting, as their root systems can grow throughout the winter before emerging in spring.

If you have poorly drained soil, you may want to wait until spring to plant perennials requiring good drainage (e.g. penstemon and lavender). Once the weather has cooled down, it is also a good time for dividing established perennials, though October is the more common month for that.

It is finally time for planting spring blooming bulbs! Tulips, daffodils, Hyacinth, Allium, Crocus and many others are available for purchase starting in September. While you’re refreshing flower beds and containers with pansies or other fall color, add a few spring flowering bulbs as an investment in next year’s show.

Some bulbs can also be grown in pots, often indoors, during the late autumn and winter. This process  is known as “forcing”. The most common bulbs used for forcing are paperwhites (Narcissus ‘Zeva’) and Amaryllis. While they can be started as early as September, most people prefer to wait until October for amaryllis and November for paperwhites. Other people start a few more paperwhites every week to extend the season of enjoyment.

September is a good time for starting a fresh round of cool-season and overwintering crops. This includes lettuce, spinach, and other greens—as well as some cole crops such as broccoli and cauliflower. Short season root crops, such as radishes, can be grown now to harvest before winter. Overwintering roots such as garlic and onions can also be planted.

It’s time to harvest those warm season crops! Here are some tips on harvesting different groups of vegetables:

• Melons: Most melons will detach from the vine with pressure from just one finger when ripe. Melons do not continue to ripen off the vine, so be careful not to harvest too early!
• Squash: Summer Squash are best harvested while still on the small side—not only is the flavor better, but if left on the plant a long time, it begins seed formation and reduces further fruit set. A Winter Squash is completely mature when the stem is brown and shriveled. Usually our summers don’t last long enough for that to occur. To optimize harvest, you can remove the very smallest squash and any new ones from the vine after September 1. This will allow the plant to put the remainder of its energy into ripening the larger fruit. Harvest before powdery mildew or a first frost has destroyed the leaves, and wipe the skin with a disinfecting bleach solution. Cure the skins by letting the squash air dry at room temperature for a week or so, then store them in low humidity and  at about 55°F for longest keeping.
• Eggplant: Best if picked when slightly immature, when the fruit has stopped rapidly enlarging, but the skin is still shiny and thin. Fruit set stops a week or two before the autumnal equinox, and this is when all developed fruit should be harvested. Smaller fruits may continue to ripen if the early days of October are sufficiently warm.
• Peppers: Many varieties of both sweet and hot peppers change color from green to red or yellow as they ripen–which should be used as a guide for harvest and to attain the best flavor. For thin-walled varieties of hot chili peppers intended for drying, be sure to harvest before frost or the onset of the rainy season to prevent rotting of the fruit. If the fruit has not entirely ripened by this time, pull up the entire plant and hang upside down in a cool, dimly lit place. Some of the remaining fruit on the plant will both ripen and dry under these conditions.
• Tomatoes: Tomatoes are at their peak when they easily detach from the stem with only the slightest tug. If you find yourself at the end of the season with a number of green tomatoes remaining, you can boost the ripening of larger fruit by removing all flowers and the smaller, immature tomatoes. You should do this around September 1. You can also start withholding water in late August or early September. This stress will cause the plant to ripen its fruit, thinking that it must hurry to ripen its seeds for reproduction. Watch out for late summer rains, however, which can cause fragile vines to fall apart and become diseased.

As noted above, September marks the beginning of the second planting season. While it is possible to plant trees and shrubs in the heat of summer, it is often easier on the plant if you wait until the temperatures cool somewhat in September or October. Additionally, our native clay soil is often easier to dig in after the first significant shower of the autumn.

We always stock up on conifers this time of year. Many of these are quite unusual and this is the only time of year that we get some of them. Be sure to stop by frequently to see what we have in new arrivals.

Caterpillar damage is at its height in autumn. While many of the less damaging leaf eaters can be ignored because leaves will soon be dropping, tent caterpillars can do extensive damage if ignored. A large population can kill major branches of mature trees. Common targets include birch, ash, and maple. Insecticidal sprays can keep the population low.

Most trees and shrubs don’t want to be fertilized this time of year. The only exception might be a little organic, slow-release food for newly planted evergreens, or those plants that have not been fed in a long time.

This is the month for renovating summer-weary lawns. First, you should dethatch if you have not done so in the last year. This is done by thoroughly raking out the dead matter underneath the growing grass blades. Then, assess how full your lawn really is and make appropriate plans to reseed, overseed (applying seed to an existing but patchy lawn), or install sod.

If your lawn is really patchy or almost nonexistent, reseeding is best. Turn the soil and mix in some compost. Level it out and add seed, fertilizer, and lime. Cover the seed with a very thin layer of fine compost (avoid big, woody chunks). IF you keep moist and keep the weeds away, you should have a great lawn before winter.

If you are over-seeding, skip the bit about turning the soil. Still, a thin layer of compost on top is beneficial before laying the seed, fertilizer, and lime. If you’re installing sod, turn and amend the soil beforehand, then fertilize and add lime after installation.