Fall Garden Q&A
Posted: October 21, 2011
Q: I noticed that my forsythias have some flowers. Why are they blooming now?
A: The occasional blooms seen in autumn on normally spring-flowering plants such as crabapple, quince, viburnum, lilac, and forsythia are generally the result of summer stress. Considering the growing season just winding down, it’s not surprising that plants were stressed.
A period of very hot and dry weather in midsummer was sandwiched between a very wet spring and a very wet fall. Because of summer heat and drought, plants may enter a period of slight dormancy; the return of rain and better growing conditions in fall then tricks plants into thinking it’s spring again and time to bloom. Fall flowering is generally sparse and not harmful to the plant, and there are usually still plenty of buds for next spring’s blooming.
Early spring-flowering shrubs and trees in temperate climates generally produce their flower buds in response to the long days of summer; but those buds remain tightly closed until after a period of dormancy induced by the cold temperatures of winter. Once the plant senses that temperatures are warming into spring, the buds then swell and burst into flower. This is the normal cycle; but this year’s anything but normal weather has fooled some plants into flowering out of season.
Q: Is it too late to sow grass seed now?
A: According to Penn State, sowing later than mid-October is not recommended. Late summer into early fall is generally the best time to establish a lawn from seed. The problem with seeding after October 15 is not that it’s too cold for the seed to germinate or that the seedlings are cold-sensitive; after all, most of our turf grasses are varieties that prefer cooler temperatures. The problem is that the young plants don’t have enough time to establish a good root system before the ground freezes; so they get heaved out of the ground during freeze and thaw cycles during winter, then dry out and die.
If you have bare patches, you can try seeding now, but results may be sparse and you may need to seed again in spring; or you can cover the areas with mulch now to prevent erosion and then wait until spring to sow your turf grass seed.
I mow grass longer or shorter in the fall?
A: According to the turf specialist at Penn State, the most important factor in fall lawn mowing is to continue to mow regularly until the grass enters dormancy, and then to make a final cut before winter, once the top growth has slowed to a crawl, generally in mid to late November. Turf that is left too high going into winter can become matted down, which can lead to early spring disease problems such as snow mold.
Maintain your mowing height within the recommended range for most turfgrasses; between 2.0 and 3.0 inches is recommended for fall. Do not cut the grass too short (less than 1.25 inches) or too high (more than 3.0 inches). So a final mowing of the season at 2.0 to 2.5 inches is fine for the lawn.
When spring comes and you start mowing again, our turf expert recommends mowing frequently enough to not leave a lot of clippings on the lawn; that may mean twice-weekly mowing. But do not remove too much leaf blade each time you mow. The rule of thumb is to cut off no more than one-third of the total leaf surface at any mowing.
Q: The needles of my pine tree are turning yellow this fall. What’s wrong with my tree?
A: The needles of “evergreen” conifers don’t last forever, and older needles are shed in the fall after they turn yellow. This is a natural process. As long as the needles turning yellow are on the interior of the tree, and the younger needles on the outer part of the tree are still green and healthy, nothing is wrong with your tree.
This natural needle drop is most noticeable on Eastern white pine, which holds its needles for only two years. Other pine species may hold their needles longer, up to 5 years; and spruce trees generally keep their needles for 5 to 7 years before shedding the oldest ones.
If entire branches or needles at the tips of branches are yellow, brown, or dead, then something else is happening to your tree. This might be environmental or cultural stress, or insect or disease problems.