Tree Care
Root Stimulator vs Mycorrhizal Fungi for Tree Planting
The Challenge of Transplant Shock
Planting a new tree is one of the most rewarding investments you can make in your landscape. However, the transition from a controlled nursery environment or a dense forest floor to your backyard is incredibly stressful for the tree. This stress, commonly known as transplant shock, occurs when a tree loses a significant portion of its root system during the harvesting and moving process. According to the University of Minnesota Extension, the primary cause of transplant shock is the severe reduction in the root-to-shoot ratio, leaving the tree unable to uptake sufficient water and nutrients to support its existing canopy.
To combat this, gardeners and arborists often turn to soil additives at the time of planting. The two most popular categories of products are hormone-based root stimulators and mycorrhizal fungi inoculants. While both aim to improve transplant survival rates, they work through entirely different biological mechanisms. In this guide, we will compare a leading hormone product (Fertilome Root Stimulator) against a leading biological product (Plant Success MycoGrow) to help you decide which is best for your specific planting scenario.
Product A: Hormone-Based Root Stimulators
Hormone-based root stimulators, such as the widely available Fertilome Root Stimulator & Transplanting Solution, rely on synthetic plant hormones called auxins. The primary active ingredients are typically Indole-3-butyric acid (IBA) and Naphthaleneacetic acid (NAA). These compounds mimic the natural hormones a plant produces to signal root cell division and elongation.
How It Works and Application
When a tree is transplanted, the physical damage to the root tips halts natural growth. Applying an auxin-rich solution directly to the root ball and surrounding backfill soil forces the tree to prioritize the regeneration of fine feeder roots over top-growth (leaves and branches). Fertilome also includes a mild, low-nitrogen fertilizer blend (usually around 4-10-3) to provide immediate phosphorus for root energy without burning the delicate new tissues.
- Cost: Approximately $15 for a 32-ounce concentrate.
- Measurements & Mixing: Mix 1.5 ounces (about 3 tablespoons) per gallon of water. A single 32-ounce bottle can treat up to 48 newly planted trees or shrubs.
- Timing: Apply only once at the exact time of planting as a soil drench. Over-application can actually stunt root growth due to hormone toxicity.
Product B: Mycorrhizal Fungi Inoculants
Mycorrhizal fungi inoculants, such as Plant Success MycoGrow Soluble, take a biological approach rather than a chemical one. Mycorrhizae are naturally occurring fungi that form a symbiotic relationship with plant roots. Research highlighted by Michigan State University Extension indicates that while mycorrhizal fungi are vital for long-term tree health, their presence is often severely depleted in disturbed urban and suburban soils.
The Symbiotic Network
When you apply a product like MycoGrow, you are introducing millions of endomycorrhizal and ectomycorrhizal spores directly to the root zone. Once these spores germinate, they attach to the tree's roots and send out microscopic hyphal threads into the surrounding soil. These threads act as an extension of the root system, increasing the tree's absorptive surface area by up to 1,000%. This network is exceptionally efficient at scavenging for water, phosphorus, and micronutrients that the tree's own roots could never reach.
- Cost: Approximately $25 to $30 for a 1-pound bag of soluble powder.
- Measurements & Mixing: Mix 1 ounce of powder per gallon of water for a root dip, or use 1 pound per 100 gallons of water for large-scale soil drenching.
- Timing: Apply at planting. The spores require direct physical contact with the roots to colonize effectively. Unlike hormones, there is no risk of toxicity if you use too much.
Head-to-Head Comparison Chart
| Feature | Hormone Root Stimulator (Fertilome) | Mycorrhizal Inoculant (MycoGrow) |
|---|---|---|
| Primary Mechanism | Chemical signaling (Auxins) to trigger cell division | Biological symbiosis to expand root surface area |
| Best For | Bare-root trees, cuttings, and severe root loss | Balled-and-burlapped (B&B) trees and disturbed soils |
| Speed of Results | Fast (Initiates root growth within days) | Slow (Takes weeks to establish fungal network) |
| Longevity | Short-term (Degrades in soil within weeks) | Long-term (Fungi live and grow with the tree) |
| Drought Resistance | Indirect (More roots = better water uptake) | Direct (Hyphae extract tightly bound soil moisture) |
| Cost Per Tree | ~$0.30 per tree | ~$0.15 per tree (highly concentrated) |
Scenario Guide: Which Product Should You Choose?
Choosing between a root stimulator and mycorrhizal fungi largely depends on the type of tree you are planting and the condition of your soil.
Scenario 1: Planting Bare-Root Trees or Cuttings
If you are planting bare-root fruit trees, shade trees, or propagating from cuttings, hormone-based root stimulators are the superior choice. Bare-root trees have suffered massive trauma to their fine feeder roots during the nursery digging process. The immediate application of IBA and NAA forces the tree to push out new root tips quickly before the canopy desiccates. The mild fertilizer kickstart also provides the energy required for this rapid cellular division.
Scenario 2: Planting B&B Trees in Urban or Compacted Soil
If you are planting large Balled-and-Burlapped (B&B) specimens or container-grown trees in newly graded, compacted, or urban soils, mycorrhizal inoculants are highly recommended. Urban soils are often stripped of their topsoil and biological life during construction. By introducing mycorrhizae, you are rebuilding the soil food web. The fungi will help the tree access tightly bound phosphorus and water in heavy clay soils, providing long-term drought resistance that a one-time hormone drench cannot offer.
Can You Use Both Products Together?
Yes, you can use both products in tandem, and many commercial landscapers do exactly this. Because they operate through completely different pathways—one chemical and one biological—they do not cancel each other out. However, if you are on a budget, you must prioritize based on the tree's immediate needs. Use the root stimulator for trees with visibly damaged or minimal root systems, and use the mycorrhizal fungi for trees with intact root balls that are moving into poor-quality native soil.
Expert Planting Tips Beyond Additives
While root stimulators and mycorrhizal fungi are excellent tools, they are not magic cures for poor planting techniques. Experts at The Morton Arboretum emphasize that proper watering and mulching are the ultimate determinants of transplant success. To ensure your additives work effectively, follow these critical steps:
- Find the Root Flare: Never plant a tree too deep. The root flare (where the trunk widens at the base) must be slightly above the surrounding soil grade. Planting too deep suffocates roots and renders both hormones and fungi useless.
- Watering Protocol: Additives need moisture to activate. After applying your drench, water the tree deeply to settle the soil and eliminate air pockets around the root ball.
- Proper Mulching: Apply 2 to 3 inches of organic wood chip mulch over the root zone to retain moisture and regulate soil temperature. Keep the mulch at least 3 inches away from the trunk to prevent rot and rodent damage.
- Avoid High-Nitrogen Fertilizers: Do not apply standard lawn fertilizers or high-nitrogen granular feeds to a newly planted tree. Nitrogen pushes top-growth (leaves), which the compromised root system cannot support, worsening transplant shock.
By understanding the distinct biological roles of hormone root stimulators and mycorrhizal fungi, you can tailor your planting strategy to give your new trees the absolute best chance at thriving for decades to come.
