As the snow melts deliciously into the parched soil, an early spring stroll through the yard is an opportunity to evaluate conditions and microclimates that exist on your property. In gardening, microclimates are the climates of small areas. For example, one area is shaded, but a spot just a few feet away is in full sun. As a result, the temperature at midday between the two spots might vary by as much as 10 or 15 degrees.

Microclimates are often defined by the orientation of your property to the sun. A northern exposure has shade year-around and is conducive to plants that can withstand northeastern winds, frozen soil that is late to warm up, moisture retention and lack of sunshine. "Winter hardy" and "shade loving" best describe plants for these areas.

Southern exposures receive more sun and are much hotter. This increases soil evaporation, causes earlier snow melt, and usually results in drier soils and increased plant transpiration. As a result, early spring bulbs and new growth can be vulnerable to a killing frost. But because the soils stay warmer longer, we can also enjoy a longer growing season in this microclimate. Generally plants that do well in a warmer climate, may do well with a southern exposure. For example, plants that are hardy to Zone 5 or 6 may be very happy here if provided protection in the winter.

The southern and western exposures are the sunniest and warmest areas in the yard. A western exposure is usually hot in the afternoons with very dry soil. This is the area for hardy plants that like dry soil and warm temperatures. Protection may be needed for young trees because the warmth of the afternoon sun in the winter followed by cold nights can damage plant tissue. This can be observed as a wound in the bark of young trees. Colorado winds are generally out of the west and this area may be ideal to plant wind breaks.

Eastern exposures receive sun in the morning all year. In summers, the shade is a welcome relief in the afternoon. Soils will stay moist longer and there is more protection from the winter winds and freezing temperatures. Plants that like moist soil and part sun do well with an eastern exposure.
Take advantage of buildings, fences, walls, shrubs, and trees. Place plants where they will benefit from these protective structures. Fences, walls, and rocks affect the sun and shade. Buildings and sidewalks will wrap plants in a blanket of warmth. Dark colors can collect and hold heat releasing it after the sun goes down while light colors reflect daytime heat and light back onto plants. The color of paved surfaces and mulch will also have an effect. Dark mulch will warm the soils earlier in the spring.

High walls will shelter plants from the wind and can change the wind pattern by blocking wind from some areas and funneling it into others. A windbreak of trees and shrubs that acts as a filter rather than a barrier might be a better choice.

Consider topography when planning berms, slopes and entire hillsides. Warm air rises and cool air sinks creating frost pockets. Allow for air drainage just as you would for water drainage. The soil is usually rockier and more course along the top of a slope. Therefore, it drains well and holds less moisture. Generally, the steeper the slope, the drier the soil. The opposite exists at the bottom of a slope. The soil will be more moist, and because of runoff and erosion from the top, finer and higher in nutrients. Use of retaining walls helps to level slopes and reduce runoff.

By identifying and understanding just how all the variables of microclimates combine, it will open possibilities for plants that might not have been considered. In Colorado's semi-arid climate, gardeners can accommodate gorgeous plants and flowers that make the yard water efficient, less of a struggle to maintain and sensitive to the landscape.

Q: Horseradish is one of my favorite herbs. I use the hot, biting taste to spice up meals. As I do not see horseradish in many of my neighbor's gardens, how does this pungent plant grow?

A: Horseradish (Armoracia rusticana) is a deep taproot herb related to cabbage. It grows as a perennial in Zones 5-9 and as an annual in other zones. Do not put it in a vegetable garden that gets tilled every year. A corner of the herb garden in full sun is ideal or planted by itself, as it tends to send up shoots all over the place. Horseradish should be planted in early spring, as soon as the soil can be worked. Also it can be planted in late fall similar to garlic. Soil pH should be 5.5 to 7. The plant will grow approx. 24" tall and 18" wide. Dig a hole twice as deep as the roots of the plant. Hold the plant over the hole as you refill the dirt, keeping the base of the leaves at the soil line. Water the plant well. The compost in your back -fill soil should give the horseradish most of it's food for the season, but if needed apply a balanced or low-nitrogen fertilizer 2 or 3 times during the season. For the most pungent flavor do not harvest until the leaves have seen frost. Leave a few roots three-fourths inch wide by ten inches long for next year.

Q: What is the difference between pre-emergent herbicides and postemergent herbicides when it comes to controlling weeds?

A: A dense and healthy grass is the best way to reduce weeds, but a totally weed-free lawn is rarely attainable. Pre-emergent means the weed seeds have not yet germinated. To be most effective, a pre-emergent herbicide must be applied before seed germination, usually late March and early April along the Front Range. Warm, moist springs cause earlier germination and cool, dry springs delay germination. Pre-emergent herbicide application will not control the weed once it begins to form leaves and should not be used when planting grass seed as the grass seed will also be affected. Postemergent herbicides are used after germination and the weeds begin to mature. These herbicides are most effective against young seedling weeds. Once the herbicide is applied according to directions, use good cultural practices (proper fertilization, mowing and irrigation) to encourage rapid fill-in of the grass. Herbicides are only one tool in a total weed control program. Also, see Fact sheets #3.100, Broadleaf Weed Control in Lawns; #3.101Grassy Weed Control in Lawns; #7.202, Lawn Care.

Q: Where did all these weeds come from?

A: Weed seeds spend the winter blowing from place to place and they wash in with surface water. Weeds come from newly added soil and organic matter such as compost and manure. Birds and other wildlife are great distributors of weed seed. Some weed seeds have longevity of twenty-five years. Gardeners often allow weeds to go to seed. Each time the garden is tilled new weeds are brought to the surface and old weeds are cut up and multiplied. Gardeners who do not allow weeds to go to seed will have fewer weeds next year. An application of mulch also helps suppress weed seed germination.

Starting seeds indoors is fun and can give you a head start on plants going into the garden. Check the seed packages for special directions such as refrigerating the seeds for 24 – 48 hours before planting or soaking or "nick"ing hard coated seeds to make germination easier. Also check to see if the seeds need light to germinate or complete darkness - cover those flats with newspaper or keep in a dark space like a closet until the seeds germinate.

Horticultural oils are highly refined petroleum or vegetable oils diluted with water and applied as a spray on fruit or shade trees and woody ornamental plants. Applications made before trees leaf out will control over-wintering aphids, eggs of leafroller and tent caterpillars, mites and scale insects. Apply when the temperature is above freezing. The oil blocks the insects' air holes and they suffocate.

Although it has been unseasonably warm, it is hard to believe our average last frost date is May 10 – 15 in Fort Collins, Loveland and Berthoud. Don't be too anxious to put out those frost sensitive plants like tomatoes, peppers and squash without keeping some protection handy. You know in Colorado it can be 70 degrees in the morning and 30 degrees by noon!

April is the month that bare root plants are available at the nurseries. You'll find dormant trees, shrubs, roses and small fruits like raspberries, grapes and strawberries and dormant asparagus crowns. This is a great time to find less expensive plant material for a hedge. Keep the packing material moist and the plants away from direct sunlight until you are ready to plant.

Jonquil, narcissus, daffodils – the differences between them are almost impossible to distinguish. We all agree though that their arrival means spring has arrived. "Jonquil" comes from the Spanish jonquillo (rush), describing the rush-like leaves. "Narcissus" was a youth in Greek mythology who drowned after admiring his own beauty in his reflection in a pond and turned into the flower and "daffodil" may have come from the British mis-pronunciation of the flower "asphodel" that they preferred to their own native "daffodil".

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

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This page updated:  April 27, 2004