Thursday, August 15, 2019

Planning Ahead

By Andie Wommack, Douglas County Extension

While it’s still too early to be planting bulbs in your garden, it’s never too early to be thinking about what you might like to plant. The growing season this year was much different than ones we’ve seen here on the Front Range in the past few years. Some plants thrived with the cooler temperatures and extra moisture at the beginning of the season, and others struggled. Are you noticing some bare spots in your landscape, or are there areas you’d like to renovate? Bulbs can offer a variety of color and interest to your landscape.

Early September is the best time to buy bulbs to be planted from mid-September through late October. Bulbs need time to root before the ground freezes or they may not bloom uniformly in the spring. Did you know that bulb size has a direct correlation with flower size? That’s why it’s best to be able to choose bulbs from open bins rather than prepackaged bulbs, so you have more control over the product quality. This also allows you to inspect each bulb for any damage or mold.

Have you ever thought about, or wondered where these bulbs come from? They’re grown on farms just like other crops. Bulb farms are popular tourist attractions when the flowers are in bloom. Holland is one of the most famous locations for bulb farms, but there are plenty in the states as well.

Western Washington is home to several different bulb farms. I lived near several during my student teaching. Thankfully I did my student teaching during the spring semester so I had the opportunity to attend one of their festivals. Online resources say that planting solid blocks of color are more impressive from a distance than a mixture of colors and varieties. This is true in a home landscape, and it is immensely impressive on a large-scale bulb farm.

Monday, August 12, 2019

Fall pollinator feast by Irene Shonle

Many of our gardens peter out in the dog days of summer. We go great guns in the spring, snapping up anything that is blooming at the garden center, desperate for the color after a long winter.  But we often forget that summer keeps going, long after we have wilted.
And this can be a problem for pollinators - they need to find nectar and pollen for the entire season, not just the spring.

Here are some suggestions for fall blooming plants that will keep your pollinators happy until frost:

First, some native suggestions:
Showy Goldeneye
Showy goldeneye (Viguera multiflora). These plants cover themselves in small yellow blooms that butterflies and bees visit. Bonus points: they also provide seed for small songbirds later in the season.

Tansy aster
Tansy aster (Machaeranthera bigelovii). Short lived perennials that love dry disturbed areas, and keep out noxious weeds.  Super easy.
Gumweed (Grindelia squarrosa).  Just as easy as useful as the tansy aster for pollinators - and if you plant them together, you have a vivid combination!

Goldenrod (Solidago spp.) This maligned plant is not the allergy culprit that many people believe, and it is one of the top host plants for native bees!  Easy to grow.

Rabbitbrush (Chrysothamnus spp.). These plants are known for their brilliant fall blooms as well as being a butterfly magnet.  Good winter interest to boot!

Spotted gayfeather (Liatris punctata). Beautiful feathery wands of purple also lure in butterflies.

Maximilian sunflower (Helianthus maximiliana). Tall and narrow, this plant is covered with showy yellow sunflowers for pollinators (and later for birds). Very drought tolerant.

And then some non-native suggestions

Russian sage (Perovskia atriplicifolia) is a bit overused, but is good for dry spots and for pollinators. Can spread a little more than you may like.

Coneflowers (Echinacea spp.). Most aren’t native to Colorado, but they are sure to draw lots of butterflies and bees.  Many, many cultivars and colors to choose from.

Catmint (Nepeta spp). I would suggest using a sterile variety such as Six Hills Giant. If you cut them back after their first flush of bloom, they usually rebloom. Bumblebees love them, and deer and rabbits leave them alone. Drought tolerant.
Catmint Six Hills Giant with a happy bumblebee

Fall blooming sedums such as Autumn Joy (Sedum spectabile). These are drought tolerant low-growing plants with clusters of pink flowers beloved by butterflies.

Zinnias - very colorful annuals (grow from seed) to attract butterflies and bees.

Mark your calendars and save the date! The 5th annual Landscaping for Colorado Native Plants will be at the Auraria Campus on Feb 29th! Leap into gardening with native plants!

Thursday, August 8, 2019

When to worry about evergreen needle drop

By: Emily Jack-Scott (Garfield County Colorado Master Gardener)

In late summer and early fall evergreen trees often have needles that dry out and shed. This can be alarming for gardeners, and it can be difficult to tell if early needle drop is cause for concern or just part of the evergreen tree’s annual needle shed. In this blog post we’ll review some signs and symptoms of when summer needle drop in evergreens could be indicative of underlying health problems.

It is typical for all evergreen trees to shed out old needles in the fall. Fall needle drop is usually preceded by yellowing of old (often interior) needles. Sometimes needle drop happens in early summer, especially if a tree has been recently transplanted. Trees can lose up to 90% of their roots when transplanted, which seriously hampers the tree’s ability to provide its needles with vital water and nutrients. Therefore it is common in the first few years after transplant for a new tree to have needles that turn yellow or brown weeks or even months before they typically do in fall.

Premature needle drop in newly transplanted evergreen trees is especially common in interior needles. Evergreen needles often turn a pale sickly shade of green during transplant shock. Once needles discolor, they never recover their original dark green or blue hues. Instead, the tree will retain the weakened discolored needles for several years until the tree has put on enough new healthy growth that it no longer requires the old weak needles for photosynthesis. At this point, the old interior needles will turn yellow or brown and soon after drop off. In spruces and pines, interior needle shed is common August – November. In these instances, summer needle shed is not usually cause for concern.

There are, however, some instances when summer needle shed and discoloration may be symptoms of more concerning health threats such as beetle activity, mites, fungal disease, root damage, or winter burn/injury.

Beetle Activity

When bark beetles such as mountain pine beetle or spruce beetle attack their respective host trees, they first chew through the bark and then tunnel around beneath the bark in the thin layer of the tree’s growing tissue known as the cambium. This can result in sudden red discoloration of needles (in pines), or slow and steady browning and dropping of needles (in spruces). To tell if needle discoloration is caused by beetle activity, look for other symptoms of bark beetles such as small entry holes in the tree’s trunk (with or without sap), fine sawdust (or frass) collecting in the bark or base of the trunk, and/or thin sap streamers dripping down the trunk of the tree.

Once trees have been attacked by bark beetles, there is little that can be done to prevent the decline and death of trees. But there are preventative sprays and pheromone packets available for trees that have not yet been attacked. These can be used in areas where bark beetle activity is high.


Another critter that can cause extensive discoloration of needles is the humble spider mite. Spider mites cause extensive damage and stippling to affected needles as they feed on their host’s sap. Colorado blue spruces are especially prone to spider mites. Webbing may even be visible on heavily infested branches. Improving the general health of affected trees is recommended. Miticide sprays are available to treat heavy infestations.

Fungal Diseases

Spruce and pine trees can be prone to several fungal infections that can lead to needle discoloration and early drop. One of these fungal infections is known as cytospora canker, which primarily affects Colorado blue spruces. Needle discoloration from cytospora is typically purple or rust-colored, primarily on lower branches of mature spruce trees. Cytospora canker also causes resin-covered cankers on affected branches.

Another common fungus in Colorado that can cause needle discoloration and shedding is rhizosphaera needle cast. Rhizosphaera needle cast primarily affects Colorado blue spruce but can also affect lodgepole and ponderosa pines. Needle discoloration caused by rhizosphaera will typically start off yellow in mid-summer, turning to reddish-purple in late summer, before turning brown and shedding out. Spruces and pines affected by rhizosphaera needle cast will lose their interior older needles, leaving only the current year’s growth (which has not yet been infected). Infected needles are often covered in tiny black dots running lengthwise, which are the visible fruiting bodies (pycnidia) of the fungus.

There are preventative fungicide sprays available that can prevent spreading of fungal infection to new growth and unaffected trees in the vicinity. Timing of these sprays is critical, so be sure to carefully follow fungicide directions. Cultural treatments such as removing fallen needles and creating better airflow through tree canopies are also recommended.

Root Damage

If the discoloration and shedding of needles occurs in a spiral pattern up the tree, there is a good chance the premature needle drop is the result of root damage. Trees tend to spiral slightly as they grow (twisting slowly over time in response to prevailing winds). So when a root is damaged, it is unable to provide vital nutrients and water to the living tissue it is connected to running up the length of the tree in a slightly spiraled pattern. This results in the spiral pattern of dieback from damaged roots.

Root damage can be difficult to troubleshoot, since they are not visible below ground. But common causes of root damage include root girdling, root severing/damage from digging (e.g. utility repairs or sidewalk installations), or damage from absorption of salt, chemicals, or pesticides. Needle drop from root damage can be isolated, and the tree will recover in time. The exception to this is when roots have been girdled, in which case the tree will continue to lose needles and will likely need to be removed if the girdling root(s) cannot be isolated and removed.

Winter Injury

Winters in Colorado can often be very cold, with heavy snowfall and strong winds. The thin wax coat on needles is all that protects evergreens from succumbing to harsh winter conditions. It’s no wonder that after particularly bitter winters, some evergreens show signs of winter injury by way of discolored needles. This can be especially true when affected trees endured stressful conditions in the summer growing season before (e.g. transplant, drought), limiting its ability to grow thicker waxy needle coatings. Winter injury can often present itself in a pattern, such as all the needles on the windward side of the tree showing discoloration. Discoloration from winter injury is often reddish-purple in hue.

This has been a review of some of the more common biotic or abiotic causes of premature discoloration and dropping of evergreen needles. There are other causes of needle drop, such as nutrient deficiencies and soil conditions that can also cause problems. If in doubt of the cause of your needle discoloration, contact your local Colorado Extension office or a certified arborist for more information or a site visit. 

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