Dear Sheila,

Thank you for contacting the UNH Extension Infoline regarding your Boxwoods winter damage.

Following up on your emAIL from 4/9/2026, I’ve attached some general information to help get you started.

We are committed to finding the right solution for your lawn and garden and are happy to provide further guidance as needed.

Please feel free to reach out with any further questions.

Best regards

Haim
Master Gardener Volunteer
UNH Extension Infoline Team

General information:

For boxwoods in New Hampshire that have suffered significant winter damage, the "window" pruning technique—officially known as thinning—is the correct step to encourage inner growth. To help your shrubs fully recover, follow these next steps based on professional landscaping practices:

1. Refine Your Thinning (Window) Cuts

Now that you have cut a window, ensure you have used selective thinning rather than just a single hole. [1]

• Encourage Light: Reach into the canopy and remove several small "hand-sized" chunks of outer foliage. This allows sunlight and air to reach the dormant buds on the inner stems, which is the only way to trigger green growth in the hollow center.
• Technique: Use sharp, disinfected hand pruners to cut individual branches back to a healthy lateral branch or bud. This directs new growth to fill the gap rather than just growing outward.

2. Monitor for Dead Wood

Winter damage in NH often includes bark splitting due to extreme temperature swings.

• The Scratch Test: Use your thumbnail to scratch the bark of a branch that looks dead. If the tissue underneath is moist and green, it is alive and can still push out leaves. If it is brown and dry, that branch is dead and should be removed entirely.
• Remove "Straw" Wood: Any stems that are completely straw-colored or have peeling/cracked bark will not recover and should be pruned back to live wood.

3. Support Recovery with Care

• Fertilization: Apply a slow-release, balanced fertilizer (like a 10-10-10) in late March or early April once the ground has thawed. This provides the energy needed for the "rejuvenation" you are seeking.

• Watering: NH boxwoods often die in winter because they dry out (winter burn) while the ground is frozen. Ensure they receive roughly 1 inch of water per week throughout the growing season and keep watering in the fall until the ground freezes.

• Mulching: Maintain a 2–3 inch layer of mulch around the base (but not touching the stems) to protect the shallow root system from further temperature fluctuations.

4. Future Protection

To prevent a repeat of the damage from two years ago:

• Winter Wrapping: In late fall, after the first hard frost, loosely wrap your boxwoods in burlap to protect them from drying winds and harsh winter sun.
• Avoid Late Pruning: Do not do any heavy pruning or fertilizing after July, as this encourages tender new growth that will be killed by the first NH freeze.

Information Sources:
This advice is based on expert horticultural guidelines from :

https://www.canr.msu.edu/news/browning-of-boxwood-is-it-boxwood-blight

https://hort.extension.wisc.edu/articles/boxwood-blight/

https://extension.umd.edu/resource/boxwood-identify-and-manage-common-problems/

Question 2:

To determine your soil's current fertility levels, I suggest having it tested. University extension services, such as the UNH Soil Testing Service or the UConn Soil Lab, strongly recommend a soil test before applying nutrients to identify specific deficiencies.

https://extension.unh.edu/agriculture-gardens/pest-disease-growing-tools/soil-testing-services

https://scholars.unh.edu/cgi/viewcontent.cgi?article=2783&context=extension&preview_mode=1&z=<personal data hidden>

For most crabapple trees, a balanced 10-10-10 fertilizer is the best general-purpose choice. However, the "best" fertilizer depends on the age of your tree and its current growth performance.

Recommended Fertilizer Types

• Young Trees (1–6 years old): Use a balanced 10-10-10 granular fertilizer. If you notice slow growth (less than 12–18 inches annually), you may increase the nitrogen.
• Established Trees: Mature trees often require less nitrogen to avoid excessive leaf growth at the expense of blossoms. A 5-10-10 ratio or a lower nitrogen lawn fertilizer (without weedkillers) is often recommended.
• Organic Options: Well-rotted manure, compost, or organic blends like 5-3-4 are excellent for long-term soil health.
• Newly Planted Trees: Avoid high-nitrogen fertilizers during the first year to prioritize root establishment over canopy growth.

When and How to Apply

• Best Timing: Apply fertilizer in early spring before new growth begins (typically March or April). A second light application can be made in June if needed.
• Avoid Fall Feeding: Late-season fertilization can trigger a flush of new growth that won't harden before winter, leading to "tip dieback" from frost.
• Application Method: Broadcast the fertilizer evenly on the soil surface starting about one foot from the trunk and extending slightly beyond the drip line (the edge of the branches). Water the area thoroughly after applying to help nutrients reach the roots.

Important Precautions

• Fire Blight Risk: Excessive nitrogen can make crabapples highly susceptible to fire blight, a serious bacterial disease. If your tree is already growing vigorously, you may not need any fertilizer at all.
• Lawn Competition: If your tree is growing in a lawn that is already regularly fertilized, it is likely already getting all the nutrients it needs.
• Soil Testing: University extension services, such as the UNH Soil Testing Service and the UConn Soil Lab, strongly recommend a soil test before applying nutrients to identify specific deficiencies.

https://soiltesting.cahnr.uconn.edu/suggested-fertilizer-practices-for-trees-shrubs-vines-and-groundcovers/#:~:text=The%20timing%20of%20fertilizer%20applications,early%20June%20and%20late%20September.

https://www.uaex.uada.edu/yard-garden/in-the-garden/reference-desk/fruits/fertilizing.aspx#:~:text=For%20young%20trees%2C%20in%20early,important%20for%20all%20fruit%20trees.&text=All%20links%20to%20external%20sites,that%20they%20are%20not%20satisfactory.