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Ask the Master Gardener: Acclimate hardy annuals for cooler temperatures

Cold-tolerant annuals are those that can withstand cooler temperatures, even temperatures slightly below freezing.

Pansies in a flower pot covered in snow.
Pansies can be acclimated to the cold as a hardy annual plant.
Contributed / Jennifer Knutson

Dear Master Gardener: What exactly does “cold-tolerant annual” mean? Pansies are arriving in stores — isn’t it too early to put them out?

Answer: An annual is a plant that survives only one season in our climate, needing to be replaced every year. Cold-tolerant annuals, also known as hardy annuals, are those that can withstand cooler temperatures, even temperatures slightly below freezing. When you purchase pansies in the spring, acclimate them to the outdoors by setting them outside during the day when the temperature is above 40 degrees and bringing them inside at night. After several days, they should be able to handle the cooler temperatures, even a light frost. Pansies can tolerate a few degrees below freezing, so they are typically the first annuals you see in the stores.

Dear Master Gardener: What can you tell me about using microclover instead of grass in shade areas and for pollinators?

Answer: Microclover refers to smaller varieties of white clover. All clovers are legumes and are thus able to transform atmospheric nitrogen gas into a form of nitrogen that can be used by plants. Before the introduction of broadleaf herbicides in the 1950s, clover was a valued component of lawn seed mixtures due to its ability to fix nitrogen, enrich the soil, and improve turfgrass growth. It also provides food for bees. Because of these valuable characteristics, there is a renewed interest in using microclover in lawns. The University of Maryland conducted research on microclover used in combination with turf-type tall fescue and determined these advantages and disadvantages to its use:

Advantages of microclover:

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  • Mixes well with turf-type tall fescue (and Kentucky bluegrass) and provides a uniform appearance;
  • Provides an organic source of nitrogen (in grass clippings and as it decays) to support turfgrass growth; may reduce one nitrogen application per year;
  • Flowers provide a food source for bees.

Disadvantages of microclover:

  • Does not tolerate high heat and drought; starts to die when cool-season turfgrass enters dormancy in the summer; requires reseeding for persistence;
  • Top growth dies back in the winter which can leave bare spots and lead to erosion;
  • Poor shade tolerance;
  • Seeds are expensive and not readily available in retail stores;
  • Most broadleaf herbicides labeled for use on tall-fescue will kill microclover;
  • Bees attracted to the flowers may be undesirable for people with bee sting allergies;

In conclusion, the University of Maryland says that microclover can be included as a component of lawns, but there is no current research that supports its successful use exclusively as a groundcover or lawn alternative.
Dear Master Gardener: Can I reuse my potting soil from last year?

Answer: Yes, as long as whatever you were growing in it was healthy. Add some compost or rotted manure, or some additional potting soil or slow-release fertilizer to get the nutrient levels back up.

Dear Master Gardener: My clivia has a couple large off-shoots. Should I leave them or cut them from the main plant? How do I do that and when?

Answer: Clivia is an elegant plant with long-lasting orange or yellow flowers. It’s a member of the amaryllis family. When your plant is about three or four years old it will produce one or more offsets each year. Leave the offsets on the parent plant for a year or two to make sure it is mature enough to make it on its own. You can separate an offset from the parent plant when it has three or four leaves. The best time to divide a Clivia is after it has finished blooming in the spring. Remove the plant carefully from the pot, gently loosen the roots, and brush off excess soil so you can see the division area better. Hold the two crowns of the plants you want to divide and carefully pull them apart, making sure that each plant has a good root system intact and a portion of the rhizome. Pot the new plant and repot the parent plant.

Dear Master Gardener: This year I would like to grow Ranunculus in my cutting garden. Do I need to do anything special?

Answer: Ranunculus is a gorgeous flower with a vase life often exceeding ten days! In our cold climate it can be started in a hoop house or low tunnel in early spring, then planted outside. Flower farmers and other commercial gardeners usually grow them in a greenhouse. To pre-sprout it before planting it in the ground, soak the corm in room temperature water for three to four hours to plump it up. Then, fill a flat-bottom seed tray half full of moist potting mix. Cover the soaked corms (you can place them close together) with one inch of moist potting mix. Place the tray in a cool place (50-55 degrees) for 10-14 days. When white roots are visible, the corms are ready to plant. A Ranunculus usually starts flowering about 90 days after planting.

You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.

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