Dear Master Gardener: When is it safe to plant annuals?

Answer: Warm May temperatures may tempt you into planting your annuals too early. The last frost date for our area is approximately May 27 (there will only be a 10% chance of frost occurring after that date). Begonia, coleus, impatiens, salvia, zinnia and vinca need warm soil and air temperatures to grow well and will not tolerate any frost. These plants will grow much better when put out at least one or two weeks after the last frost-free date. Ageratum, geranium, dianthus, lobelia, petunia and gazania can tolerate cool air temperatures and soil, but cannot take a light frost without being damaged, so plant them close to the last frost-free date. Annuals that can tolerate cool soils and air temperatures and even light frost are pansies, calendula, dusty miller, snapdragons and sweet alyssum. They can be planted a few weeks before the last frost date.

Dear Master Gardener: This year for Mother's Day instead of buying my wife roses, which don't last very long, I thought I would buy a hardy rose that can be enjoyed for years. Are there roses that grow in our area and can withstand our cold winters without much fuss?

Answer: Yes, there are some excellent roses from which to choose that are hardy to zone 3b (temperatures to 35 degrees below zero). It is important to check the plant label to make sure it is hardy to zone 3. Here are a few excellent choices by color:

• White: Marie Bugnet and Morden Blush

• Pink: Suddenly Summer, Morden Bell, William Baffin, Foxi, and Prairie Joy

• Red: Hope for Humanity, Winnipeg Parks, and Champlain

Canadian Artist roses are hardy to zone 2: Emily Carr (dark red), Felix Leclerc (deep pink), Bill Reid (yellow), Campfire (tri-color) and Oscar Peterson (white). Although Easy Elegance roses are listed as hardy to zone 4, many do fine in 3b and carry a two-year guarantee.

Plant your rose in a sunny location that receives at least five to six hours of sunlight each day; morning sun is preferred. Roses need protection from strong, drying winds but require lots of air circulation to reduce the chance of disease. Hardy roses do not typically need any extra winter protection since they will regrow from the roots if the canes are damaged.

Dear Master Gardener: What do the numbers on the fertilizer package mean?

Answer: The three numbers on a fertilizer package correspond to the percentage of three elements: nitrogen, phosphorus and potassium. For example, a 10-10-10 fertilizer, which is often used in the spring to fertilize many flowering shrubs, has 10% nitrogen, 10% phosphorus and 10% potassium. Fertilizers add nutrients to the soil to help plant growth. In order to accurately fertilize your lawn, garden and landscape plants, it is beneficial to get your soil tested. Soil testing provides information on the availability of nutrients in the soil and whether soil amendments are needed. As of April 15, the cost of a soil test at the University of Minnesota Extension is $17. Instructions can be downloaded from:

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fertilizer is high in nitrogen to encourage green growth, and by law cannot contain the middle number, phosphorus, because the runoff is bad for our lakes. Lawn fertilizer in the garden will cause lots of green leaves but few vegetables or fruits.

Dear Master Gardener: Which shrubs have edible fruits, other than a blueberry?

Answer: Please make sure you have correctly identified a shrub before using the fruit for cooking and eating, especially when collecting fruit from the wild. Following are some shrubs with edible fruits that are found in home landscapes and other areas of Minnesota.

• Currant fruit ripens in late June and July. There are red, white and black varieties. Red Lake was developed by the University of Minnesota and has a mild flavor. White Imperial Currant has the sweetest and richest flavor. Consort, a black currant developed in Canada, has a sweet musky flavor. Currants are used for making jam and jelly.

• Gooseberry fruit ripens in July and August. The berries are round, greenish-white to reddish-purple and used in jam, jelly and sauce.

• Serviceberry, also known as Juneberry or Saskatoon, is a shrub or small tree that grows anywhere from 4-25 feet in height. Some serviceberry species are native to Minnesota. The small, round, purple fruit can be eaten fresh or used for jam, jelly, pie and sauce.

• Elderberry berries are round, purplish-black and ripen in late summer and early fall. The fruit is used for jelly, pie and wine.

• Highbush Cranberry, which is not a cranberry, has edible berries that are round to oblong, yellow to dark red and ripen in September. The berries are sour and bitter eaten fresh, but are used for jelly and sauce.

• Chokecherry is a tall shrub or small tree that can be found throughout Minnesota. The round, dark purple berries ripen in July and August. Eaten fresh, the fruit has a very astringent taste, but they are often used for jelly, preserves, syrup, pie and wine.

• Sandcherry is found in sandy, rocky areas throughout Minnesota. The round, purplish-black berries ripen in July and August. This is another astringent tasting berry that is used for sauce and wine.

• Pin Cherry is a tall shrub or small tree found in burned-over regions and wooded areas. The fruit is round, bright red and ripens in July and August. The berry has a single seed or pit inside and tastes sour when eaten fresh. It is used to make jelly, syrups and wine.

Dear Master Gardener: I planted a Pink Diamond Hydrangea six years ago. Last year it didn't look very good and didn't flower much. Is there something I can do to make it look as good as it did the first few years?

Answer: Hydrangea paniculata "Pink Diamond" is one of many wonderful hydrangeas that is hardy to zone 3 and easy to grow. Like all panicle hydrangeas, it performs best in full sun to part shade. These hydrangeas develop their flower buds on new wood, so they can be cut back severely in the spring to maintain their size. You can cut it back to the ground, or cut it back to one to three feet if you want a taller plant, and your plant will still produce flowers. You may need a pruning saw to prune stems that are 1/2 inch or larger.

Dear Master Gardener: What ground cover do you recommend for a shade garden?

Answer: Canadian wild ginger, hardy to zone 2, is a lovely choice because the velvety, heart-shaped leaves look good from spring to autumn. It does get an insignificant, reddish-brown flower that is hidden below the leaves. It spreads and colonizes shady spots very well and performs best in moist, but well-drained soil in medium to heavy shade. It is a "deer resistant" plant.

Wintergreen, which is native to Minnesota, is a great evergreen groundcover that grows 2 to 6 inches high. It should be planted in part to full shade and can tolerate pretty heavy shade. The bell-shaped, white flowers bloom in July, then give way to edible bright red berries that persist through winter. The leaves and fruit have the smell and taste of wintergreen and were the source of all wintergreen flavoring before modern science produced it synthetically.

May Gardening Tips

• Put plant supports in place for peonies, balloon flower, delphinium and other tall, floppy plants before they get too tall.

• Prune spring-flowering shrubs right after they are done blooming so they have time to set flower buds for next spring.

• Attract butterflies to your yard by planting nectar-producing flowers such as Asclepias (butterfly weed), Monarda (beebalm), Nepeta (catmint), Echinacea (coneflowers), Liatris, Russian sage and zinnias. Protect bees and butterflies by avoiding the use of pesticides in the garden. Don't bother putting up a butterfly house because butterflies will never inhabit them. They sleep high up in trees, nestled in the safety of leaves.

• Time to get your hummingbird feeders out. Ruby-throated hummingbirds arrive around the first week in May.

• Be on the lookout for signs of fourlined plant bugs - they become active in May. Their feeding causes dark, round sunken spots about 1/16 - 1/8-inch-wide on leaves. They are found on many plants, but most commonly on mint, basil, Liatris, azalea, dogwood, forsythia, viburnum and amur maple. They won't kill the plant, but can make it look unsightly. Pick them off and crush them or drop them into a bucket of soapy water.

• Peas, leaf lettuce, spinach and radish seeds can be sown directly into the garden the second or third week in May. Transplant onions and members of the cabbage family (cabbage, cauliflower, broccoli) while soils are still cool. Wait until the beginning of June when both air and soil temperatures are warm before planting tomatoes, peppers and eggplants.

• Harden off plants started indoors or in a greenhouse before planting them outdoors by setting them in a shaded, protected area during the day and bringing them indoors at night. Avoid direct sunlight until plants are outdoors full-time.

• When the soil warms up, you can begin planting gladiola corms, and canna and dahlia rhizomes. Wait until late May or early June to plant caladium corms, begonia tubers and transplants of tender bulbs outdoors.

• May is a good time to plant grass seed. For good results, rough up the soil first. Unfortunately, this will expose crabgrass and other weed seeds that will also sprout up. Right after seeding apply a specially formulated version of pre-emergent herbicide that clearly states it is meant for newly seeded lawns, so it doesn't kill your desired grass seeds, too.

• Children may enjoy planting sunflower seeds and watching the cheery, fast-growing plants grow throughout the summer. At the end of the summer the seeds can be harvested and roasted for a tasty treat. Read the book The Sunflower House by Eve Bunting with your children or grandchildren and they may be inspired to create their own sunflower playhouse.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.