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Sulfur (S) is essential to the growth of higher plants; however, research on S fertilizer requirements for container-grown nursery tree species has not been established. The purpose of this study was to determine the substrate solution S concentration that maximizes the growth of container-grown pin oak (Quercus palustris Münchh) (pin oak–K₂SO₄ experiment) and japanese maple (Acer palmatum Thunb.) (japanese maple–K₂SO₄ experiment) in a pine bark (PB) substrate. Both species were fertilized with solutions supplying a range of S concentrations (0, 1, 2, 5, 10, 20, 40, or 80 mg·L^–1) using K₂SO₄. Regression analysis revealed that dry weights of both species were near maximum at the predicted application concentration of 30 mg·L^–1 S, which corresponded to about 15 and 7 mg·L^–1 S in substrate solution for pin oak and japanese maple, respectively. In a Micromax, FeSO₄, lime experiment, S was supplied to pin oak via a preplant micronutrient sulfate fertilizer or FeSO₄ in limed or unlimed PB. When the PB pH was relatively low (4.5, unlimed), FeSO₄ and the preplant micronutrient fertilizer were effective in supplying ample S. However, when the PB pH was relatively high (6.1, limed), the preplant micronutrient fertilizer with micronutrients in a sulfate form was more effective in supplying S and micronutrients than FeSO₄.

Pine tree substrate (PTS), for container plant production, is a relatively new alternative to the commonly used pine bark and peat substrates. Fertility management requires knowledge of nitrogen transformations in this new substrate. The objective of this study was to document the occurrence of nitrification in PTS and to determine if nitrification and density of nitrifying microorganisms are affected by substrate storage time and lime and peat amendments. Pine tree substrate was manufactured by hammermilling chips of ≈15-year-old loblolly pine trees (Pinus taeda L.) through two screen sizes, 4.76 mm (PTS) and 15.9 mm amended with peat (3PTS:1 peat, v:v, PTSP). Pine tree substrate and PTSP were amended with lime at five rates and a peat–perlite mix (4 peat:1 perlite, v:v, PL) served as a control treatment for a total of 11 treatments. Substrates were prepared, placed in plastic storage bags, and stored on shelves in an open shed in Blacksburg, VA. Subsamples were taken at 1, 42, 84, 168, 270, and 365 days after storage. At each subsampling day, each substrate was placed into 12 1-L containers. Six of the 12 were left fallow and six were planted with 14-day-old marigold (Tagetes erecta L. ‘Inca Gold’) seedlings; all containers were placed on a greenhouse bench. Substrates were also collected for most probable number (MPN) assays for nitrifying microorganism quantification. Substrate solution pH, electrical conductivity (EC), ammonium-N (NH₄-N), and nitrate-N (NO₃-N) were measured on fallow treatments. Marigold substrate solution pH, EC, NH₄-N, and NO₃-N were measured after 3 weeks of marigold growth. Nitrate-N was detected in fallow containers at low concentrations (0.4 to 5.4 mg·L⁻¹) in PTS in all limed treatments at all subsampling days, but in the non-limed treatment, only at Days 270 and 365. Nitrate-N was detected in the fallow containers at low concentrations (0.7 to 13.7 mg·L⁻¹) in PTSP in the 4- and 6-kg·m⁻³ lime rates at all subsampling days. Nitrite-oxidizing microorganisms were present in PTS at all subsampling days with the highest numbers measured at Day 1. Ammonium-to-nitrate ratios for the marigold substrate solution extracts for both PTS and PTSP decreased as pH increased. This study shows that nitrifying microorganisms are present and nitrification occurs in PTS and PTSP and is positively correlated to substrate pH.

A pine tree substrate (PTS), produced by grinding loblolly pine trees (Pinus taeda), offers potential as a viable container substrate for greenhouse crops, but a better understanding of the fertilizer requirements for plant growth in PTS is needed. The purpose of this research was to determine the comparative fertilizer requirements for chrysanthemum (Chrysanthemum ×grandiflora ‘Baton Rouge’) grown in PTS or a commercial peat-lite (PL) substrate. The PTS was prepared by grinding coarse (1-inch × 1-inch × 0.5-inch) pine chips from debarked loblolly pine logs in a hammer mill fitted with 3/16-inch screen. The PL substrate composed of 45% peat, 15% perlite, 15% vermiculite, and 25% bark was used for comparative purposes. Rooted chrysanthemum cuttings were potted in each of the substrates on 15 Oct. 2005 and 12 Apr. 2006 and were glasshouse grown. Plants were fertilized with varying rates of a 20N–4.4P–16.6K-soluble fertilizer ranging from 50 to 400 mg·L⁻¹ nitrogen (N) with each irrigation. Plant dry weights and extractable substrate nutrient levels were determined. In 2005 and 2006, it required about 100 mg·L⁻¹ N more fertilizer for PTS compared to PL to obtain comparable growth. At any particular fertilizer level, substrate electrical conductivity and nutrient levels were higher for PL compared to PTS accounting for the higher fertilizer requirements for PTS. Possible reasons for the lower substrate nutrients levels with PTS are increased nutrient leaching in PTS due to PTS being more porous and having a lower cation exchange capacity than PL, and increased microbial immobilization of N in PTS compared to PL. This research demonstrates that PTS can be used to grow a traditional greenhouse crop if attention is given to fertilizer requirements.

Containerized seedlings of eastern redcedar (Juniperus virginiana L.) were fertilized weekly for 175 days with a solution containing 50 ppm P, 150 ppm K, and either 0, 5, 10, 20, 40, 80, 160, 320, or 640 ppm N. Plant height, stem diameter, and shoot and root dry weights increased asymptotically with applied N; 640 ppm N diminished response. Growth after 175 (height, stem diameter) and 180 (shoot and root dry weights) days was optimal (90% of maximum) at N concentrations of 115, 155, 230, and 105 ppm, respectively, 1.5% foliar N optimized height growth. Foliar concentrations of N, P, and K increased in treated plants over the duration of the experiment, while Ca, Mg, and Mn decreased or remained constant. Starch concentration of fertilized plants decreased sharply after initiation of the experiment, but controls showed little change during the first 120 days. Sucrose concentration remained constant over the summer but increased sharply in late fall. At 180 days, foliar concentrations of starch, sucrose, hexose, N, P, K, and B increased asymptotically with applied N; concentrations of Ca, Mg, and Mn decreased.

Pine tree substrate (PTS) is a relatively new alternative to the commonly used pine bark and peat-based substrates for container crop production. Physical and chemical properties of freshly manufactured PTS have been studied; however, this new substrate will sometimes be manufactured and stored for later use by growers. The objective of this research was to determine how chemical and physical properties of PTS were affected by storage duration with or without amendments of limestone or peatmoss. We also studied how the growth of marigold was influenced by PTS storage time and by lime and peat amendments. Substrate properties studied were pH, cation exchange capacity (CEC), electrical conductivity (EC), carbon-to-nitrogen ratio (C:N), bulk density (BD), and particle size distribution. Pine tree substrate was manufactured by hammermilling chips of ≈15-year-old loblolly pine trees (Pinus taeda L.) through two screen sizes, 4.76 mm (PTS) and 15.9 mm [amended with peat (PTSP)]. Pine tree substrate and PTSP were amended with lime at five rates and a peat–perlite mix (PL) served as a control treatment. Substrates were prepared, placed in plastic storage bags, and stored on shelves in an open shed in Blacksburg, VA. Substrates were subsampled at 1, 42, 84, 168, 270, and 365 days after storage. At each subsampling day, twelve 1-L containers were filled with a subsample of each treatment. Six of the 12 were left fallow and six were planted with 14-day-old marigold (Tagetes erecta L. ‘Inca Gold’) seedlings. Substrate was also collected for analysis of CEC, C:N, BD, and particle size distribution. The pH of non-limed PTS decreased during storage, and at least 1 kg·m⁻³ lime was needed to maintain PTS pH 5.4 or greater over the 365-day storage period (Day 1 pH = 5.8) and 2 to 4 kg·m⁻³ was needed to maintain PTSP pH 5.4 or greater for 365 days (Day 1 pH = 5.2). EC measurements were highest at Day 1 (1.02 to 1.21 dS·m⁻¹) in all treatments and decreased by Day 42. Cation exchange capacity decreased over time in non-limed PTS and PTSP. Carbon-to-nitrogen ratio and BD remained the same over time for all treatments. There were minor changes in particle size distribution for limed PTS. Marigold growth in all limed PTS and PTSP treatments was equal to or greater than in PL, except at Day 1; the lower growth in PTS and PTSP at Day 1 compared with PL suggests that freshly manufactured PTS may contain a phytotoxic substance that was not present in PTS by Day 42. Pine tree substrate and PTSP are relatively stable when stored as described previously, except for a pH decrease that can be prevented with additions of lime before storage.

Three experiments were conducted to determine the feasibility of using Biobarrier, a landscape fabric with trifluralin herbicide-impregnated nodules, of various sizes to prevent root escape of trees from the drainage holes of 56-liter containers in below-ground pot-in-pot (P&P) and above-ground Keeper Upper (KU) nursery production systems. In addition, side holes or slits were cut in some container walls to test the effect of Biobarrier on the prevention of circling roots. In Expt. 1 (P&P), Betula nigra L. `Heritage' (river birch) trees with no Biobarrier had root ratings for roots escaped through drainage holes that indicated a 5-fold increase in numbers of roots than for treatments containing Biobarrier. All Biobarrier treatments reduced root escape and resulted in commercially acceptable control. In Expt. 2 (KU), control and the Biobarrier treatment river birch trees (30 nodules) had commercially unacceptable root escape. In Expt. 3 (P&P), control and 10-nodule treatment Prunus × yedoensis Matsum. (Yoshino cherry) trees had commercially unacceptable root escape, but treatments containing 20 and 40 nodules resulted in commercially acceptable control. Biobarrier did not limit shoot growth in any of the experiments. The results of these experiments indicate that Biobarrier did not prevent circling roots, but sheets containing at least 8 or 20 nodules of trifluralin acceptably prevented root escape from drainage holes in the pot-in-pot production of 56-liter container river birch trees and Yoshino cherry trees, respectively.

Recent interest in the use of wood substrates in horticulture crop production has justified the need for determining fertilizer requirements in these substrates compared with traditional pine bark (PB) and peatmoss substrates. The objective was to determine the response of japanese holly (Ilex crenata Thunb. ‘Compacta’) and azalea (Rhododendron obtusum Planck. ‘Delaware Valley’) grown in a pine tree substrate (PTS) (trade name WoodGro™) or milled PB to fertilizer rate. Pine tree substrate is produced from freshly harvested loblolly pine trees (Pinus taeda L.) that are delimbed, chipped, and ground in a hammer mill to a desired particle size. Japanese holly plants were grown in 2.8-L containers in the fall of 2005 and again in the spring of 2007 with the addition of azalea. Plants grown in PTS or PB were fertilized by incorporating Osmocote Plus fertilizer (15N–3.9P–10K) at rates of 3.5, 5.9, 8.3 or 10.6 kg·m⁻³ for japanese holly and 1.2, 3.5, 5.9, or 8.3 kg·m⁻³ for azalea. After 3 months, shoot dry weights were determined for japanese holly and azalea. Japanese holly root dry weights were determined for both experiments, and substrate CO₂ efflux (μmol CO₂ m⁻²·s⁻¹) was measured on the treatments at the end of the experiment using a LI-6400 soil CO₂ flux chamber. In 2005, japanese holly shoot dry weights of PTS-grown plants were comparable to plants grown in PB at the 8.3 kg·m⁻³ fertility rate, and shoot dry weights of PTS-grown plants were higher than PB at the 10.6 kg·m⁻³ rate. In 2007, japanese holly and azalea shoot dry weights of PTS-grown plants were comparable to PB plants at the 5.9 kg·m⁻³ fertilizer rate. Both japanese holly and azalea achieved shoot growth in PTS comparable to shoot growth in PB with ≈2.4 kg·m⁻³ additional fertilizer for PTS. Substrate CO₂ efflux rates were higher in PTS compared with PB indicating higher microbial activity, thereby increasing the potential for nutrient immobilization in PTS.

The objective of this study was to evaluate the landscape performance of annual bedding plants grown in a ground pine tree substrate (PTS) produced from loblolly pine trees (Pinus taeda) or in ground pine bark (PB) when transplanted into the landscape and grown at three different fertilizer rates. Begonia (Begonia ×semperflorens-cultorum) ‘Cocktail Vodka’, coleus (Solenostemen scutellarioides) ‘Kingswood Torch’, impatiens (Impatiens walleriana) ‘Dazzler White’, marigold (Tagetes erecta) ‘Bonanza Yellow’, petunia (Petunia ×hybrid) ‘Wave Purple’, salvia (Salvia splendens) ‘Red Hot Sally’, and vinca (Catharanthus roseus) ‘Cooler Pink’ were evaluated in 2005, and begonia ‘Cocktail Whiskey’, marigold ‘Inca Gold’, salvia ‘Red Hot Sally’, and vinca ‘Cooler Pink’ were evaluated in 2006 and 2007. Landscape fertilizer rates were 1 lb/1000 ft² nitrogen (N) in 2005 and 0, 1, and 2 lb/1000 ft² N in 2006 and 2007. Visual observations throughout each year indicated that all species, whether grown in PTS or PB, had comparable foliage quality in the landscape trial beds during the growing period. With few exceptions, dry weight and plant size for all species increased with increasing fertilizer additions, regardless of the substrate in which the plants were grown. For the unfertilized treatment, when comparing plant dry weight between PB and PTS for each species and for each year (eight comparisons), PTS-grown plant dry weight was less than PB-grown plants in three out of the eight comparisons. However, there were fewer differences in plant dry weight between PTS- and PB-grown plants when fertilizer was applied (PTS-grown plants were smaller than PB-grown plants in only 2 of the 16 comparisons: four species, two fertilizer rates, and 2 years), indicating that N immobilization may be somewhat of an issue, but not to the extent expected. Therefore, the utilization of PTS as a substrate for the production of landscape annuals may be acceptable in the context of landscape performance.