The silvery-blue needles of a Colorado blue spruce (Picea pungens) are one of its most recognizable and desirable traits.
This striking hue makes the tree a standout in the landscape and sets it apart from the sea of green found in most conifers.
Blue pigmentation is rare in the plant world, and when a blue spruce starts to turn green, it’s understandably disappointing.
The change in color doesn’t always indicate a serious problem, but it typically points to specific environmental or cultural factors affecting the tree.
In our guide to growing blue spruce, we cover how to cultivate these striking specimens in your landscape.
This article breaks down the main reasons why a blue spruce may turn green, ranging from natural aging to pollution and nutrient deficiencies, so you can pinpoint what’s affecting your tree.
7 Reasons Why Blue Spruce Turns Green
We aren’t going to cover reasons for yellowing, browning, or other discoloration of the foliage. This guide addresses the issue of the needles turning green.
First let’s talk about where the coloration comes from.
The distinctive blue hue on P. pungens needles comes from a layer of waxy coating called cutin that covers the green chlorophyll-rich tissue underneath.
This coating, often referred to as the cuticle, acts as a barrier that protects the needles from UV rays, moisture loss, and pests.
The intensity of the color depends on the thickness of the cuticle, which can vary among cultivars. It can range from nearly silver to very bright blue.
Anything that damages the cuticle or stops it from developing will cause the needles to look green.
1. Age
As needles age, the cuticle naturally wears off, exposing the green beneath. It’s completely normal for older interior needles – those closer to the trunk or lower on the branch – to appear greener than newer growth at the tips.
This color shift doesn’t indicate a health issue, it’s part of the tree’s natural aging process.
New needles will typically emerge with the characteristic blue coloration, assuming environmental conditions are favorable and the tree is otherwise healthy.
Different cultivars show variation in how long they retain their color, which is directly related to how thick and persistent the cuticle is.
Cultivars with a thicker wax layer such as ‘Hoopsii’ or ‘Fat Albert’ tend to maintain their color longer than others.
2. Air Pollution
Airborne pollutants such as ozone, sulfur dioxide, and nitrogen oxides can strip or prevent proper development of the cuticle on spruce needles.
When this happens, the exposed foliage appears green rather than blue.
This is most common in urban or industrial areas. Affected needles won’t regain their color, but new growth may still emerge blue if the tree is otherwise healthy.
Unfortunately, you can’t really fix this problem except to reach out to your local government and fight for better environmental protections in your area.
While that’s always a great idea, it might not be feasible for everyone. In that case, enjoy the green foliage or plant a different species.
3. Excess Moisture
Excess moisture on the foliage, from frequent overhead irrigation or prolonged rainy weather can gradually wear away the waxy coating.
Occasional rain won’t cause noticeable damage, but chronic moisture exposure may lead to the erosion of the cuticle and the needles turning green.
Whenever possible, use drip irrigation or water at the soil level to keep foliage dry.
4. Low Light
Blue spruce trees need full sun to maintain the waxy, colorful coating on the foliage.
When they’re shaded – by buildings, other trees, or dense planting – new growth may not develop the waxy cuticle so it will appear more green.
If your tree has become shaded over time, consider thinning nearby vegetation to restore optimal light exposure.
5. Natural Weathering
Beyond the natural aging process and excess rain, environmental factors such as wind and sun exposure can gradually erode the waxy cuticle on blue spruce needles.
The speed of this change can vary depending on the cultivar and local climate, but it’s a normal part of growing this species outdoors.
As long as the tree is otherwise healthy and producing blue new growth each year, weathering alone is not a cause for concern.
6. Nutrient Deficiency
If none of the other causes on this list seem to fit, it’s possible your tree is experiencing a nutrient deficiency, and you’ll want to test your soil.
Potassium and magnesium deficiencies can cause leaves to lose their color and turn pale green or even yellow.
When this happens, the older growth is typically affected first, while the newer growth remains blue. That’s because the tree prioritizes available mobile nutrients to the new growth and lets the older growth die off.
Calcium and nitrogen deficiencies, on the other hand, usually affect new growth. These nutrients are immobile, meaning the plant can’t redirect them from older tissue to support developing shoots.
As a result, the newest needles may appear pale or yellow and drop from the tree.
Discolored foliage is always a good reason to conduct a soil test, but routine testing every year or two is wise even if your plants appear healthy.
You can reach out to your local university extension office and they can help you obtain a test from a regional lab that understands your native soil conditions.
Alternatively, you can purchase test kits online.
Keep in mind that nutrient availability isn’t just about what’s present in the soil.
If the soil is compacted or overly wet, or if the roots are suffering from rot or damage, the tree may not be able to absorb the nutrients it needs.
In such cases, deficiencies can still occur even in nutrient-rich soil.
7. Pesticides
Certain pesticides and dormant oils can strip the waxy coating from blue spruce needles, causing them to lose their coloration and turn green.
It’s an unfortunate tradeoff – treating pests can unintentionally remove the tree’s natural protection.
If you need to apply these treatments, expect some color loss, but don’t panic. The hue will return with new growth as long as the tree remains healthy.
Sometimes Being Blue is Best
Blue spruces stand out because of their unusual coloring, so it’s obviously a big disappointment when they lose that distinctive hue.
Are you having trouble figuring out what’s causing the color change in your plant? Fill us in on the situation in the comments section below and include a few pictures if you can. We love to help!
And for more information about growing conifers in your landscape, check out these guides next:
