Monday, April 16, 2018

Soil Temperature


by Sandy Hollingsworth 
In talking with other Master Gardeners, I’ve found some faithfully rely on soil temperature when planting while others take their chances. I know I’ve been guilty of impatience planting root vegetable seeds, then later tomato and pepper seedlings, too early, then watching them sit doing nothing and never catching up to the ones I waited to plant at a happier, warmer time. The warm sun can make the top of the soil feel warm enough, but down several inches it’s another story. This year I decided to invest in a thermometer to poke into my containers, prepped soil and raised beds to check before planting. I found a 5-inch-long metal stem pocket thermometer, with a probe sheath for storage. It happens to be in centigrade but that is okay as it is easy enough to figure out the conversion to Fahrenheit.

When reading up on recommended planting temperatures I found this summary: “Soil temperature is the best indicator of when to plant each type of vegetable, no matter what climate zone you live in”, said Annie Chozinski, Oregon State University vegetable researcher. “Crops that germinate in the coolest soils (down to 40 degrees F) include arugula, fava beans, kale, lettuce, pak choi, parsnips, peas, radicchio, radishes and spinach seed. When the soil temperature reaches above 50 degrees, Chinese cabbage, leeks, onions, Swiss chard, and turnips can join them in the garden.  At 60 degrees you can sow warm-season vegetables such as beans, beets, broccoli, Brussels sprouts, cabbage, carrots and cauliflower.”

If you are not at higher altitudes with a short growing season like 9300’ at the Gilpin County CSU Extension community gardens, or if you have a warm greenhouse, you’ll want to wait until the soil warms to 70 - 80 degrees to plant warm-season vegetables, or start them inside well in advance. These include tomatoes, eggplants, peppers, melons, tomatillos, cucumbers, corn and squash. Some mountain residents with pockets of warmer micro-climates may be able to grow these warmer season vegetables, but most will be better off sticking to cool season vegetables. Even if you do have a warm micro-climate, do be aware that the harvest will be smaller than lower and warmer elevations.

Our beloved mountain grown potatoes need at least 40 degrees to sprout and be productive. In our shorter, higher altitude growing season cool weather vegetables with shorter growing times tend to be most successful.

Although it is rarely an issue in the mountains except in greenhouses, know that some plants have an upper soil temperature that they will tolerate, such as 80 degrees for lettuce and spinach, and 95 degrees for most anything including cucumbers and tomatoes. Of course, you can plant more vegetables when the soil returns to its preferred temperature if your growing season gives you enough time to harvest it, or you use row covers or other season extension techniques to help regulate the soil temperature.

Here is a sampling of Fahrenheit vs Centigrade conversion if needed:
45 degrees F = 7.2 degrees C
50 degrees F = 10 degrees C
60 degrees F = 15.5 degrees C
70 degrees F = 21 degrees C
80 degrees F = 26.6 degrees C
90 degrees F = 32.2 degrees C

Colorado State University Fact Sheets 7.244 Colorado Mountain Gardening, 7.235 Choosing a Soil Amendment, and 7.214 Mulches for Home Grounds provide more information about controlling soil temperature.  They also explain soil amendments and that reducing surface evaporation and conserving soil moisture factor into soil temperature. Raised beds warm faster plus using south facing areas will usually be beneficial to reduce temperature fluctuations if combined with enough protection from wind. 7.248 Vegetable Gardening in the Mountains includes more scientific explanations about plant base temperature “T-base” and GDU Growing Degree Units, plus tips on seed and site selection.

The thermometer will be a welcome addition to your garden tools and fun to poke around with while you wait patiently for the right time to plant.  Happy planting!

Monday, April 9, 2018

Brunnera


by Sharon Faircloth


Brunnera macrophylla w/ Matteuccia struthiopteris and  Gallium odoratum and some pushy mint
Brunnera macrophylla w/ Matteuccia struthiopteris and
 Gallium odoratum and some pushy mint

A lovely little perennial that will brighten up any area with part-sun to shade is Brunnera macrophylla.  It is a member of the Boraginaceae family also known by common names of Siberian Bugloss, Heartleaf Brunnera or False Forget-Me-Not.  My preference is Siberian Forget-Me-Not because its delicate little flowers are such a contrast to the ruggedness of our mountain terrain.  It will easily grow in Zones 3-8. 

Brunnera macrophylla Jack Frost
Brunnera macrophylla Jack Frost

The leaves are heart-shaped and come in different varieties and shades of green ranging from yellowish to very dark green.  The Jack Frost cultivar has variegated, silvery leaves.  The Diane’s Gold variety is yellow-green.  The heart-shaped leaves range from a petite size to very large elephant ear like size.  The delicate periwinkle flowers shoot up on airy little branches providing visual interest in early summer.  It’s attractive to bees and butterflies and not so much to deer, elk and rabbits! 

Brunnera, Osterich Fern and Astilbe
Brunnera, Osterich Fern and Astilbe

Brunnera provides an interesting option for ground cover in shadier areas, especially in conjunction with other groundcovers.  It prefers moist, well-drained soil but tolerates dryness once established.  Mulch will help keep the moisture in and protect from winter harshness.  While planting instructions suggest best results come with rich soil (what doesn’t??), I found the plants to be quite hardy once established.  They will grow in small mounds, up to about 12 inches tall and 12-24 inches across.  Plants will self-seed and you can also save seeds to plant in other areas or divide in the spring. 

There are several complementary spreaders (See Fact Sheet 7.413 for mountain specific ground covers at http://extension.colostate.edu/) including Lamium maculatum (Dead Nettle) which has a variegated leaf that has a stand alone interest, even when not in bloom. For people with slightly warmer microclimates,  Galium odoratum (Sweet woodruff) which is also a good spreader with different texture and fragrant little white flowers or Ajuga reptans  (Bugleweed) which has bronze, mat-forming leaves.  This combination provides contrast in color, bloom, height, while sharing the same requirements of soil and light. 

Other ideas for companion plants include Dicentra spectabilus (Bleeding heart) with bright pink or reddish flowers; Astilbe arendsii or A. japonica which also have bright pink, red, white or more subtle colorations with long lasting plume-like flowers; and Matteuccia struthiopteris (Ostrich fern) which is easy to grow and gives, yet another, texture and height that will complement the Brunnera.

Consider incorporating the subtle little Brunnera in your shady landscape and come late spring or early summer, and I think you will be so happy you did!