Time to Irrigate

With the exception of newly planted plants, I did not have to irrigate until the hot weather came at the end of June. Even now there is still moisture in the soil available for deep rooted plants. When hot weather finally comes, sometimes we panic and turn the sprinklers on every day. Again, with the exception of newly transplanted plants, daily watering is not necessary and is even detrimental in some situations. Brief daily watering keeps the top of the soil moist, which encourages weed seed germination. It also encourages moss growth on top of the soil in shady areas.

The best way to irrigate is to apply enough water to wet the entire root system of shallow rooted plants like grass. Then allow enough time for the soil to dry on top. Depending upon your sprinkler system, it usually requires a minimum of 20 minutes to apply enough water to wet the soil several inches deep. Rotating sprinkler heads may require an hour or longer.

If your soil will not accept that much water at one time without runoff, run sprinklers through the cycle twice at half the amount of time.

Run sprinklers through their cycle on a two minute cycle so you can check them at least once a month. This will allow you to catch plugged or mis-aligned sprinkler heads before dry spots develop.

You can determine how long it takes to deliver 1/3 to 1/2 inch of water using your sprinklers by placing shallow cans such as tuna fish cans on the lawn. Water for a specific interval such as 30 minutes and then measure the accumulated water with a ruler.

Run sprinklers through their cycle on a two minute cycle so you can check them at least once a month. This will allow you to catch plugged or mis-aligned sprinkler heads before dry spots develop.

Ground Covers

Ground covers are especially useful in areas where it is difficult to maintain lawn grass. Areas with deep shade, such as under large trees, sloping areas where it is difficult to mow and small or irregularly shaped areas which require a lot of trimming.

Ground covers are those plants which grow naturally close to the ground and spread quickly to fill in thickly so few weeds or other plants grow in them. Most only grow a few inches high, but some can reach a foot or more. Many perennial flowers work well as ground covers when planted thickly over a larger area. Lately I have seen “stepable” plants in nurseries. This is a group which can tolerate some foot traffic, and could be used in areas where you need to walk occasionally. However, very few ground covers will tolerate more than light foot traffic.

Some of the very best ground covers prefer part to heavy shade, so they grow well in areas where there is not enough light to grow thick lawn grass. My favorite shade tolerant ground cover is Lamium or spotted nettle. There are several varieties with variegated silver and green leaves. They all have a very long season of bloom from spring to late fall. Flowers colors range from white to pink to crimson. My favorite variety is Pink Pewter. Lamium will grow in full shade or areas with morning sun.

Ajuga is a good sun or shade ground cover which will tolerate some traffic. The most popular variety has bronze leaves, but you can also find green and a tricolor type with green, bronze and pink leaves. Most Ajugas produce blue flowers in the spring, but a pink flowered variety is also available.

Creeping Jenny will also tolerate some traffic and grows well in shady to part sunny areas. It has yellow flowers in late spring. It requires moist conditions and will not tolerate dry soils.

Sweet Woodruff is the toughest of the shady ground covers. It will crowd out almost anything. It produces tiny white flowers in the spring. It will also grow in sunny areas and will tolerate some foot traffic.

Creeping Potentilla is one of our mountain natives. It is one of the most tolerant of foot traffic and will grow from heavy shade to full sun. It has small yellow flowers in late spring and intermittently through the summer. Potentilla is also somewhat drought tolerant.

Sedum is another ground cover which will tolerate sun to shady areas. A number of drought tolerant varieties have a variety of foliage colors and textures and flowers from white to yellow to dark pink. Most will tolerate some foot traffic.

For sunny areas, the toughest ground cover we have is our native Kinnikinnik. It is drought tolerant and does well in parking strips.

Cerastium or snow-in-summer is the toughest of the sun-loving ground covers. It has silver foliage and prolific white flowers in early summer which make it look like a patch of snow. It will tolerate dry conditions and foot traffic. It will not tolerate wet areas and needs at least a half day of sun to grow well.

Moss phlox is one of the showiest ground covers. It comes in several bright colors including white, pink, lavender blue, and rose red. It blooms for several weeks starting in early spring. It also needs a half day or more of sun.

Rock cress and false rock cress are also early spring bloomers which make good ground covers. Rock cress or Arabis comes in white and pink shades. False rock cress or Aubrieta comes in pink, lavender and purple shades. Both prefer sunny areas.

If you would like help deciding where or what to plant as ground covers, please give me a call.

Last Month for Pruning Spring Flowering Shrubs

If your spring flowering shrubs such as Rhododendrons and Azaleas need pruning, do it (or have it done) by the end of July. Otherwise, some of next spring’s flower buds will be removed in the pruning process. Most spring flowering shrubs set new flower buds during late summer. Some are already developing flower buds. However, you can prune off flower buds and plants will still have time to grow new ones during August and September. If you are only concerned about reducing the size of an overgrown plant, and do not mind sacrificing flowers, spring flowering shrubs can be pruned anytime. Summer flowering shrubs (such as hydrangeas and roses) can be pruned in winter and early spring because they develop flower buds on new growth.

Bark Mulch Reduces Water Loss and Weed Sprouting

Bark dust mulch not only improves the appearance of shrub and tree beds, but reduces water loss and weed sprouting. The most common bark is from Douglas Fir trees. It is reddish brown in color, but ages to a darker brown. Hemlock bark is a darker brown color and ages to almost black. They are of equal effect in reducing water evaporation loss from the soil. They also work equally well in reducing weed seed sprouting by preventing light from reaching weed seeds in the soil. A gradual buildup of mulch over a period of years will allow plant roots to adjust by growing into the mulch. Adding several inches at one time, especially near tree trunks, can damage plants.

Line Trimmers Damage Trees

One of their more popular uses of line trimmers is to trim grass and weeds growing around trees. An occasional use around a well established tree probably does little damage. However, weekly use around trees, especially young ones, is devastating. Every time the line hits the bark of a tree, a little outer bark is removed. As fast as line trimmers rotate, that may be a hundred times in one trimming. After 20 or 30 trimmings, there may be little or no bark left.

The inner bark of a tree contains the tubes which carry food manufactured by the leaves down to the roots. If some of these tubes are damaged, less food reaches the roots. Slowing root growth means the tree can support fewer leaves. This reduces the growth rate and can actually reduce tree size as leaves are shed to balance top growth with root capacity. Once all the conducting tubes are cut, no more food reaches the roots and they begin to die. A slow, painful death of the leaves and branches follows.

The simplest way to avoid tree damage is to create a circle of mulched soil around the base of every tree which is free from grass and weeds. This should be a minimum 3 foot diameter circle for individual trees. The size of the circle should be increased with tree growth. Groups of trees and shrubs can have irregularly shaped beds around them.