Knowing when to fertilize arborvitae is one of the most important things you can do for their long-term health. Fertilizing arborvitae at the optimal time ensures the nutrients support robust growth before the harsh weather arrives. Getting the timing right helps these popular evergreens develop strong roots and dense, vibrant foliage.
This guide will walk you through the best times to feed your arborvitae, how to choose the right fertilizer, and the simple steps for application. You’ll also learn when *not* to fertilize, which is just as crucial.
When To Fertilize Arborvitae
The ideal time to fertilize arborvitae is in the early spring, just as new growth begins to emerge. This period is typically late March through early May, depending on your local climate. A second, optional application can be made in the early fall to support root development.
Spring feeding aligns with the plant’s natural growth cycle. The nutrients are immediately available to fuel the flush of new green growth. This gives the fresh foliage time to harden off before winter.
Fall fertilization, if done, should be very light and completed by mid-fall. The goal is to nourish the roots without stimulating top growth that could be damaged by frost.
Why Timing Matters For Arborvitae Health
Applying fertilizer at the wrong time can do more harm than good. Late summer or late fall fertilization can push out tender new growth that won’t survive the first freeze. This wastes the plant’s energy and can lead to dieback.
Proper timing ensures the plant uses the nutrients efficiently. It builds resilience against environmental stress, pests, and diseases. A well-timed feeding schedule is a key part of preventative care.
The Best Months For Fertilizing By Region
Your specific location dictates the exact calendar dates for fertilizing. Here’s a general regional breakdown:
- Northern Climates (Zones 3-5): Aim for late April to late May. Avoid fertilizing after early August.
- Transitional Climates (Zones 6-7): Target early to mid-April for spring feeding. A light fall application can be done in early October.
- Southern Climates (Zones 8-9): You can fertilize as early as March. A second application in early fall is often beneficial due to the longer growing season.
Signs Your Arborvitae Needs Fertilizer
Not every arborvitae needs annual fertilizer. Look for these indicators that your plant could use a nutrient boost:
- Pale green or yellowish foliage (chlorosis), especially on new growth.
- Stunted growth or significantly shorter annual growth than expected.
- Needles that appear thin or sparse.
- Overall lack of vigor, even with adequate water and sunlight.
If your arborvitae is planted in poor, sandy, or heavily compacted soil, it is more likely to need regular feeding. Healthy plants in rich soil may thrive for years without added fertilizer.
Differentiating Nutrient Deficiency From Other Problems
Yellowing needles can also be caused by overwatering, poor drainage, spider mites, or root rot. Before you fertilize, check the soil moisture and inspect the plant for pests. Fertilizing a stressed plant from other causes can worsen the problem.
Choosing The Right Fertilizer For Arborvitae
Selecting an appropriate fertilizer is just as important as the timing. Arborvitae are not heavy feeders, but they do benefit from a balanced, slow-release formula.
Understanding NPK Ratios
The three numbers on a fertilizer bag represent the ratio of Nitrogen (N), Phosphorus (P), and Potassium (K). For arborvitae, look for a balanced or slightly nitrogen-heavy ratio.
- Nitrogen (N): Promotes healthy green foliage and stem growth. This is the most important nutrient for arborvitae.
- Phosphorus (P): Supports strong root development and energy transfer within the plant.
- Potassium (K): Aids in overall plant vigor, disease resistance, and cold hardiness.
A good general-purpose ratio for arborvitae is 10-8-6 or 14-7-7. A slow-release fertilizer with a ratio like 18-6-12 is also an excellent choice, as it feeds the plant gradually.
Granular Vs. Liquid Fertilizers
Both forms have their place in arborvitae care.
- Slow-Release Granular Fertilizer: This is often the best choice for most homeowners. It is applied once or twice a year and releases nutrients slowly with watering. It provides a steady supply of food and reduces the risk of burning the roots.
- Water-Soluble Liquid Fertilizer: This acts quickly and is useful for giving a struggling plant a rapid boost. However, it requires more frequent applications throughout the growing season. It’s easy to over-apply and cause fertilizer burn.
Specialty Fertilizers: Evergreen Spikes And Organic Options
You may also consider specialized products.
- Fertilizer Spikes: These are convenient and provide localized, slow-release nutrition. You simply hammer them into the ground around the drip line. Ensure you use enough spikes to encircle the plant for even feeding.
- Organic Fertilizers: Options like compost, manure, or bone meal improve soil structure as they feed. They release nutrients very slowly. An application of compost around the base in spring is a wonderful, gentle way to feed your arborvitae.
Step-By-Step Guide To Fertilizing Arborvitae
Follow these steps for a successful and safe fertilizer application.
Step 1: Test Your Soil
A simple soil test from your local extension service is invaluable. It tells you your soil’s pH and existing nutrient levels. Arborvitae prefer slightly acidic to neutral soil (pH 6.0-8.0). The test results will guide you on exactly what type and how much fertilizer to use, preventing over-application.
Step 2: Calculate The Correct Amount
More fertilizer is not better. Always follow the label instructions on your chosen product. The amount is typically based on the size or age of the plant or the area of ground to be covered. Over-fertilizing can lead to salt buildup in the soil, root burn, excessive growth that’s prone to breakage, and pollution of waterways.
Formula For Granular Fertilizer
A common recommendation is to use 1 pound of nitrogen per 1,000 square feet of root zone per year. To find the root zone area, calculate the area under the canopy (drip line). For a single tree, you can often use the plant’s height as a guide for pounds of a balanced fertilizer.
Step 3: Prepare The Application Area
Water your arborvitae thoroughly a day or two before applying fertilizer. Moist soil helps prevent root shock and allows for better nutrient uptake. Clear any heavy mulch away from the base so you can apply fertilizer to the soil surface.
Step 4: Apply The Fertilizer
- For granular fertilizer, use a broadcast or drop spreader for large hedges, or apply by hand for individual plants.
- Spread the fertilizer evenly starting a few inches from the trunk and extending out to the drip line (the outer edge of the foliage). The majority of the feeder roots are in this zone.
- Avoid piling fertilizer against the trunk, as this can cause damage.
- If using spikes, insert them at the drip line, spacing them evenly around the plant.
Step 5: Water Deeply And Mulch
Immediately after applying granular fertilizer, water the area deeply. This washes the granules off the foliage (preventing burn) and activates the release of nutrients into the soil. After watering, replace the mulch layer to conserve moisture and suppress weeds.
Seasonal Fertilization Schedule And Considerations
A yearly schedule keeps your fertilization simple and effective.
Early Spring: The Primary Feeding
This is the non-negotiable feeding time. Apply fertilizer as the ground thaws and before the main growth spurt. The plant will use these nutrients throughout the entire growing season to produce strong, healthy foliage.
Late Spring / Early Summer: Supplemental Care
If you used a slow-release formula in early spring, no further action is needed. If your plant showed signs of deficiency mid-season, a light application of a balanced, water-soluble fertilizer can help. Cease all fertilization by mid-summer in most regions.
Early Fall: The Secondary Root Boost
If you choose to do a fall feeding, use a fertilizer lower in nitrogen and higher in phosphorus and potassium to promote root growth and cold hardiness. Apply it about 4-6 weeks before your first expected hard frost. This gives the roots time to absorb nutrients without triggering new top growth.
Late Fall And Winter: The Rest Period
Do not fertilize in late fall or winter. The plant is dormant and cannot use the nutrients. Fertilizer applied now will likely leach away with rain and snowmelt, wasting your money and potentially harming the environment.
Common Fertilization Mistakes To Avoid
Steer clear of these common errors to keep your arborvitae thriving.
Fertilizing At The Wrong Time
As discussed, late-season fertilization is a top mistake. It forces new growth that is suceptible to winter kill, weakening the plant.
Over-Fertilizing (Burn)
Excessive fertilizer salts draw moisture out of roots, causing “burn.” Symptoms include browning or yellowing of needle tips, starting on the lower branches and moving upward. If you suspect burn, leach the soil by applying several inches of water over a few days to dilute the salts.
Fertilizing Newly Planted Arborvitae
Do not fertilize at planting time. The roots are stressed and need to establish themselves. Adding fertilizer can burn tender new roots. Wait until the second growing season to begin a fertilization routine.
Ignoring Soil PH
If your soil pH is too high (alkaline), arborvitae cannot access iron and manganese, leading to yellowing (chlorosis). Fertilizer won’t fix this. You may need to apply soil sulfur or a chelated iron product to correct the pH or deficiency.
FAQ About Fertilizing Arborvitae
Can I Fertilize Arborvitae In The Summer?
It is generally not recommended. Fertilizing in summer, especially late summer, can stimulate a late growth flush that will not harden off in time for winter. The exception would be a very light application if a soil test confirms a specific deficiency and the plant is actively growing.
What Is The Best Fertilizer For Arborvitae Turning Yellow?
First, identify the cause. If it’s a nitrogen deficiency, a balanced, slow-release fertilizer can help. If the yellowing is between the veins on new growth, it may be an iron deficiency due to high soil pH, requiring a different treatment. A soil test is the best first step.
How Often Should You Fertilize Emerald Green Arborvitae?
Emerald Green arborvitae have the same needs as other varieties. Fertilize once in early spring. If they are growing well in decent soil, they may only need feeding every other year. Observe their growth and color to judge.
Is Miracle-Gro Good For Arborvitae?
Miracle-Gro offers several products suitable for arborvitae, such as their Shake ‘n Feed Continuous Release Plant Food for Trees & Shrubs. The key is to choose a product labeled for trees and shrubs or evergreens and to apply it according to the instructions and at the correct time of year.
Should You Fertilize Arborvitae In The Fall?
You can fertilize arborvitae in early fall, but it is optional and should be a light application. Use a formula promote root growth (higher in phosphorus and potassium) and apply it at least a month before the ground freezes. The primary feeding should always be in spring.
By understanding when to fertilize arborvitae and following these best practices, you provide a solid foundation for their health. Consistent, properly-timed care will result in dense, green, and resilient plants that beautify your landscape for years to come. Remember, the goal is to support the plant’s natural cycles, not to force excessive growth. With the right timing and materials, your arborvitae will thrive.