Spring Fever: When Can I Plant?

When to plant flowers and shrubs is not a calendar decision

Many people believe you shouldn’t plant until after Mother’s Day, which is the second Sunday in May. Others believe the marker is Memorial Day. Which is right? Well, both. Or, neither. You should determine when to plant spring flowers and shrubs by the soil’s temperature and dampness and the plant itself.

Workable Soil:

Not surprisingly, soil is the most important factor in your planting decision. It’s a bit of a Goldilocks thing, where the soil must be “workable,” which means the soil temperature and the amount of moisture in it need to be “just right.”

To judge moisture content, dig down about 6” and pick up an egg-sized handful of soil. Roll the soil into a ball and toss it a few inches into the air, so it can land back in your hand, or roll it around in your hand if you prefer. If the soil doesn’t completely crumble, that soil is too wet. Wait to plant, because overly wet soil can rot your plant’s roots.

Soil Temperature:

The warmth of your soil is also critical. Soil is usually about 10° F lower than the air temperature, and you should use three consecutive-day temperatures to make your guess. While the required temperature varies with the plant (or seed) itself, strive for at least 65° F soil temperature. Better than averaging air temperature, however, is to go right to the soil itself.

Taking the soil temperature is easy.  You can purchase a soil thermometer (or earth thermometer) that is used for composting (temperature is critical for composting).  The thermometer costs between $10 and $15. Get a nice long steel base that will easily go into the ground and allows you to measure the temperature at 4” deep, according to the U.S. Department of Agriculture.

Plant Hardiness:

A few flowers, like pansies, have no problem with cold weather and will grow as long as the soil temperature is over 45° F. (Pansies have even been known to survive a frost!) Plants like snapdragons and petunias require that 65° F measure, even though they have probably started acclimating to the spring weather in their starter pots. As expensive as plants can be, it’s important to give them the best start. Read the cards on the plants. Impatiens, zinnias, and sunflowers want very warm temperatures to get their best start.

So, when it comes to planting a calendar mark isn’t your best bet. It all depends upon your soil, and it’s not unheard of in some areas to see a blanket of snow on Mother’s Day.