Cold Tolerant Annuals
• Semi-hardy – Annuals that are perennials in warmer zones and can actually over winter in this area during mild winters or if located in a warm, sunny or protected area. Very frost and freeze tolerant.
• Freeze tolerant – Annuals that can withstand freezing temperatures and hard frosts for short periods with little to no injury.
• Frost tolerant – Annuals can withstand light frosts and can normally be planted before the average frost-free date. Some damage to flowers and foliage can occur if temperatures fall much below freezing or if exposed to hard frosts.
• Tender – Annuals that are injured or killed by frost. Tender annuals will lack vigor in cold soil and should not be planted until after the average frost-free date has passed and the soil warms.
How to use Cold Tolerant Annuals
• Hanging Baskets
• In the landscape (Must be “hardened off” before planting)
What does “Hardening Off” mean?
• Whether you’ve brought home a batch of greenhouse produced annuals or you have homegrown them yourself, the process of “hardening off” is important. Hardening off means that you give those tender plants a chance to get acclimated to the conditions they will be exposed to when you put them in the ground. They have been relatively pampered in the greenhouse or indoor environment, so it is critical that you give them a chance to adapt to the harsh outdoor conditions before you put them in the ground. Some plants that you purchase from a commercial grower or garden center may already be hardened off.
• To harden plants, place them outdoors in a shaded, protected area where they can become accustomed gradually to bright light, warm temperatures and wind. The growing medium in the containers will dry out much more rapidly outdoors than indoors, so check it frequently and water as needed to keep it from drying out. Allowing the plants to dry down to the wilting point can help the hardening process but be sure to keep the roots from drying out or the plant may be damaged or killed. A week or two should be sufficient for the plants to harden off.
• Hardened off plants have a “hard” look and feel to the foliage. The foliage will be a darker green and may even exhibit some “purpling” or slight “yellowing”. Some leaves may have physical damage if exposed to high winds early in the hardening process. These symptoms are normal and healthy plants will quickly grow out of these conditions.
What to do if it gets really cold?
• If you have plants in hanging baskets or other containers, bring them inside.
• The following methods can be used to limit frost injury. However, protection for temperatures below 25 degrees Fahrenheit may not be possible.
• Covers. You may have noticed that plants placed under the leaf canopy of a large tree or a building overhang escape serious freeze damage, while those out in the open are killed. These covers contain the earth’s heat. On a cold night with air temperatures in the twenties, the earth’s surface at 52 degrees is like a giant heater. Wet soil transfers heat better than dry soil. Old sheets, blankets and light rugs placed over the plants may limit cold injury to annual flowers. Leaving air spaces between plants and covers increases insulation. Heavy materials that might damage the plants should be avoided. Also, avoid plastic. Plastic will transfer the cold to the plant and provides little insulating value.
• Fans. Still air cools faster than moving air. Cold air settles; circulate air near the ground.
• Sprinkling with water. Water releases heat when changed from a liquid to ice.
• Another way to exploit the heat held by water is to surround plants with five-gallon plastic pails filled with water. This simulates the protection given plants near a body of water, such as a swimming pool, river or pond.
FROST TOLERANT – Annuals that can withstand light frosts and can normally be planted before average frost-free date. Some damage to flowers and foliage can occur if temperatures fall much below freezing or if exposed to hard frosts.
FREEZE TOLERANT – Annuals that can withstand freezing temperatures and hard frosts for short periods with little or no injury.
SEMI-HARDY – Annuals that are perennials in warmer zones and can actually over winter in this area during mild winters or if located in a warm, sunny or protected area. Very frost and freeze tolerant.