Great Gardening by Sally Cunningham: Decorate outdoors now with cold-tolerant container plants - The Buffalo News

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Great Gardening by Sally Cunningham: Decorate outdoors now with cold-tolerant container plants

A few warm days, and out we came: Buffalonians in shorts and sleeveless tees, ready to run, play, grill outdoors and get the house and garden ready for summer. Spring-hungry people went to garden centers looking for plants. We want it all – now!

Realistically, as disappointed plant hunters learned this week, it is too soon to buy or even find most annuals and perennials, and if you do find them it is too soon for them to survive outside. Tender plants will do much better for you all season if you let them grow and be tended in warm area greenhouses for a while longer. Our last average frost date is around May 20, and we often have frosts on the first days of June.

There are exceptions: You can put a hanging basket near the front door in April, and you can fill the urn by the driveway to welcome your holiday guests. Some plants flourish in cold weather. You just need to know which they are.

Cold-tolerant plants

Several annuals and many perennials grow and flower superbly through cold weather and even occasional freezing nights. If you have well-prepared soil or raised beds, you can sow some seeds right along with cold-season vegetables such as peas, spinach, lettuce and kale. Try seeding sweet alyssum, snapdragons, sweet peas and calendula as soon as the soil has thawed enough to scratch up the top couple of inches. Seed packets of these and many others have planting instructions such as “Plant in the ground (X number of) weeks before last frost date.”

Today most people find it easier and more efficient to buy plants that have been started in a professional greenhouse, and they will get results sooner. In most cases the plants have been growing in hanging baskets, 3-inch pots or possibly six-packs in greenhouses or retail stores. Hardy plant types or not, they are not ready for the cold. They must be “hardened off,” meaning that they must be introduced gradually to cold temperatures. For a few days, put them outside when the temperature stays higher than 40 degrees, and move them indoors or under a porch close to the house when the temperature dips lower. Once acclimated, most cold-tolerant plants handle several frosts quite well. Pansies and violas – hardiest of them all – survive freezing.

Plant choices

• Pansies and violas: You may remember the names ‘Icicle Pansies’ or ‘Winter Pansies,’ but they are basically all perennials these days. They are bigger, hardier and have more variety than Grandma’s pansies. Enjoy them in baskets, window boxes or in the ground. Just don’t place them where they will bake in the hot summer sun.

• Primula (Primrose): A ubiquitous harbinger of spring – even in grocery stores – these can go outside very early, once they are acclimated. They will perennialize in the garden, although some multicolored cultivars will revert to yellow flowers next season. Do seek out less known, hardy Primula species and cultivars.

• Matthiola incana (Stock): They fill the air with a clove scent in many a flower show. Choose plants that have already formed flower buds, because exposure to cold soil temperatures sometimes deters bud-set.

• Lobularia ‘Snow Princess’ and kin: The greatly improved cultivars of Sweet Alyssum make great hanging baskets for a long season of satisfaction, and it has been seen flowering even in November in snow.

• Osteospermum (Cape Daisies): With crisp patterns and bright colors, these medium-sized, upright and perky annuals are great in full sun in mixed containers.

• Callibrachoa (Million Bells): Developed from petunias, these make floriferous spillers in baskets or window boxes. Remember to water and fertilize but no deadheading is needed.

• Heucheras (Coral Bells): These popular perennials are seen in annuals departments for a reason: They tolerate the cold well and mix beautifully in spring baskets. Remember to plant these (as well as primroses, pansies and snapdragons) in the ground in late summer since most cultivars – not all – over-winter well in this region.

You will find more cold-tolerant plants as well, once you start looking for them: Argyranthemum, Diascia, Nemesia, Bacopa and verbenas, now larger, more flowing and better spreading than their predecessors.

Mix baskets

In a good garden center it is really fun to choose plants that you like, and design your own combination container plants. Be sure to read labels and get help from staff, so that you put plants with similar light and water needs together. If you must have gorgeous planters by a certain date – for the house party or event – then proceed carefully.

The DIY method requires some guesswork if you don’t know the plants intimately; some may grow taller or slower or flower less than you expect. Professionals have been growing mixed baskets for many weeks already, judging the timing and growth rates carefully to give you exactly the results you want in April, May, June, July and beyond.

Enjoy the cool (or most likely quickly changing) spring season. There will be gray skies and wind, frosty nights and – almost always – snow on the daffodils. Lucky for us, through it all there will be spring flowers, undaunted.

Sally Cunningham is a garden writer, lecturer and consultant.

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