Ciscoe Morris, Seattle Times garden writer, answers readers' questions on when to pick pears, divide iris and how to get rid of moss and dandelions without using chemical pesticides.

Q: My homegrown pears don’t keep very long and rot quickly. How and when should I harvest them?

A: European pears need to be harvested before they ripen on the tree. The fruit ripens from the inside out, and if you wait to pick them until they turn yellow and feel ripe, they’ll quickly rot in storage. Pick pears when they have reached their normal size but are still green.

Test frequently to see if they’re ready for harvest by cupping your hand under a fruit and gently lifting. If the stem separates from the tree without tugging, it’s time to harvest.

Although all pears must be ripened off the tree, varieties that are ready for harvest by mid-September such as Bartlett, Orcas and Rescue don’t need cold storage, and need only to be put on the counter for a few days to be ready to eat. Stored in the refrigerator, they will keep for four to six weeks.

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European pears that ripen in late September and October, such as Bosc, Comice and Highland, must be stored for at least three weeks in temperatures below 40 degrees before being brought out to ripen on the counter. These later-ripening pears generally will keep well into January.

Q: I love my Pacific Coast iris that I planted last spring. When is the best time to divide it?

A: Pacific Coast iris is the collective name for a number of diverse species of iris native to the West Coast from California to Washington. They produce extraordinarily beautiful flowers in spring, yet share the unique ability to thrive in our cold, wet winters and bone-dry summers with little or no supplementary watering.

Unlike most other types of iris, Pacific Coast types do not require regular dividing to keep them blooming. Over the years the oldest parts just die off and disappear, but they’re replaced by new growth that produces a great flower display every spring.

Although it can be done, dividing Pacific Coast iris can be a bit risky, because cutting into the rhizomatous roots can lead to fungus problems. If you want to try to make new plants, dig and cut off a section from the side of the root structure while the plants are in active growth in late September or early October. Make sure to keep the new division well watered until fall rains begin in earnest.

Q: My lawn is looking shabby. The grass has thinned out and moss and dandelions are abundant. How can I improve my lawn without using chemical pesticides?

A: Mid-September to mid-October is one of the best times to renovate lawns. Begin by spraying the dandelions and other broad-leaf weeds with straight white vinegar from the grocery store. Vinegar is an effective weed killer, but it works only when it is used full strength on a hot sunny day. Give each weed a thorough dose of the vinegar. It will kill any grass it hits, but it won’t matter because you’ll overseed as part of the renovation.

After spraying out the dandelions, rent a dethatching machine to remove the moss; then apply a moss-control product. To avoid pesticides, look for brands that contain soap as the main ingredient.

After a week, rent a lawn aerator. Use it to pull about a gazillion plugs out of your lawn. Don’t worry about raking up the plugs because they’ll break up and disintegrate in short order. Next apply about 2 pounds per 1,000 square feet of a 50-50 mix (or as close as you can find) of perennial rye and fine fescue grass seed over the lawn.

Seed that germinates on top of the existing sod rarely survives, so rake as much of the seed into the aeration holes as possible. Now all that is required is to apply an organic lawn food and to keep the soil surface moist until the fall rains begin. Note that rental companies will deliver the dethatching machine and aerator to your home.

Alternatively, hire a lawn company to perform the dethatching and aerating for you.

Ciscoe Morris:; “Gardening with Ciscoe” airs at 10 a.m. Saturdays on KING-TV.