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Test your green thumb IQ with this gardening quiz

What is the low temperature threshold for picking late season apples? Today's quiz has the answer. David Samson / Forum News Service1 / 2
Today's gardening quiz gives the best season to divide autumn blooming perennials like fall aster. David Samson / Forum News Service2 / 2

“Close your books and take out a sheet of paper.”

I haven’t heard the words for decades, but I remember vividly how the teacher’s chilling words struck fear into the hearts of us poor, unsuspecting (and probably unprepared) students when a surprise quiz was announced. It’s easier to laugh about it when you’re no longer a student.

Twice a year, we’ve been featuring a new gardening quiz, not so much to see if we’re paying attention, but because they’re fun. The following can be answered with a few words.

Questions
  1. Does frost help or hinder the autumn color display of trees and shrubs?
  2. Is the low-temperature threshold for safely picking late-season apples 25, 30 or 32 degrees?
  3. Can parsnips be left in the garden all winter? Can potatoes?
  4. Is reusing the same potting mix in next year’s outdoor containers a recommended procedure?
  5. If seed is collected from heirloom flower and vegetable varieties, will it produce the same results if planted next year?
  6. If an old-fashioned lilac is pruned in April, will it bloom during the current growing season? Likewise, if a Potentilla is pruned in April, will it bloom the same summer?
  7. If a tomato plant tag indicates the cultivar produces ripe fruit in 70 days, does that mean 70 days from seeding, or 70 days from transplanting the tomato into the garden?
  8. When adding leaves or straw around tender perennials or roses for winter protection, should it be done before or after the soil freezes?
  9. To grow an oak tree from an acorn, is it better to plant the acorn in the fall, or wait until spring?
  10. Is it better to cut back ornamental grasses like Karl Foerster every year, or are they better left untouched?
  11. Should fall asters and other autumn-blooming perennials be divided in fall or spring?
  12. Is the traditional iris-dividing month May, August or October?
Answers
  1. While cool temperatures and bright, sunny days intensify fall foliage colors, frost hinders development as freezing temperatures interfere with the process and speed leaf drop.
  2. Apples are generally safe left on the tree down to 25 degrees, but may be damaged if temperatures drop lower.
  3. Parsnip flavor and quality are excellent if left in the ground over winter and dug immediately as soil thaws in spring. Not so with potatoes.
  4. Yes. High-quality potting mix can be reused for multiple years. Replace one-fourth with fresh, if desired.
  5. Yes, seed of heirloom flowers and vegetables will “come true” when planted the next year, unlike hybrid seed, which should be bought fresh each year.
  6. No, old-fashioned lilacs generally won’t bloom if pruned in spring, as pruning removes the preformed flower buds. Potentillas, which flower on newly produced growth, will bloom the same summer if spring-pruned.
  7. Days to maturity of tomatoes are counted from the date of garden transplanting, not seeding.
  8. Protective mulch should wait until the top few inches of soil have frozen solid.
  9. Acorns should be planted in the fall to give them the winter chilling needed to trigger growth in spring.
  10. Ornamental grasses should be cut to near ground level every spring before new growth emerges from within the clump.
  11. Autumn-blooming perennials, like fall aster, are best dug and divided in spring.
  12. Iris are traditionally divided and planted in August. September works fine also.

Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at forumgrowingtogether@hotmail.com.

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