Container production has increased rapidly in many parts of the U.S. over the past 15 years. Container production has been the fastest growing sector in the nursery industry and the growth is expected to continue. Weed growth in container-grown nursery stock is a particularly serious problem, because the nutrients, air, and water available are limited to the volume of the container. The extent of damage caused by weeds is often underestimated and effective control is essential. Various researchers have found that as little as one weed in a small (1 gal) pot affects the growth of a crop. However, even if weeds did not reduce growth, a container plant with weeds is a less marketable product than a weed-free product. Managing weeds in a container nursery involves eliminating weeds and preventing their spread in the nursery, and this usually requires chemical controls. However, chemical controls should never be the only management tools implemented. Maximizing cultural and mechanical controls through proper sanitation and hand weeding are two important means to prevent the spread and regeneration of troublesome weeds. Cultural controls include mulching, irrigation methods (subirrigation), and mix type. Nursery growers estimate that they spend $500 to $4000/acre of containers for manual removal of weeds, depending on weed species being removed. Economic losses due to weed infestations have been estimated at approximately $7000/acre. Reduction of this expense with improved weed control methodologies and understanding weed control would have a significant impact on the industry. Problems associated with herbicide use in container production include proper calibration, herbicide runoff concerns from plastic or gravel (especially when chemicals fall between containers) and the need for multiple applications. As with other crops, off-site movement of pesticides through herbicide leaching, runoff, spray drift, and non-uniformity of application are concerns facing nursery growers. This article reviews some current weed control methods, problems associated with these methods, and possible strategies that could be useful for container nursery growers.

Container production has many advantages over traditional in-ground (field) production, including less damage occurring to the root system when transplanted, better establishment after transplanting, decreased labor and land acquisition costs for production, and increased product availability and longevity in the retail market. Growing plants in containers, however, alters root growth and function and can change root morphology. Numerous factors influence root growth in containers. Roots of container-grown plants are subjected to temperature and moisture extremes not normally found in field production. The effects of substrate aeration (Ea) as well as water holding capacity (Pv) interact with different pot characteristics, resulting in changes to root morphology. Successful plant establishment after transplanting is often linked to root health. This review focuses on the roles of substrate physical and chemical properties, container characteristics, and temperature in altering root growth in container-grown woody nursery crops. Root circling, planting too deeply or “too-deep syndrome” (TDS), and the use of composts as container substrates will also be examined.

As limitations on water used by container nurseries become commonplace, nurseries will have to improve irrigation management. Several ways to conserve water and improve on the management of irrigation water applied to container plants are discussed in this review. They include 1) uniform application, 2) proper scheduling of irrigation water, 3) substrate amendments that retain water, 4) reducing heat load or evaporative loss from containers, and 5) recycling runoff water.

An integrated approach to weed control in nursery containers is crucial if herbicide applications during the growing season are to be reduced. This experiment, conducted in 2002 and 2003 in Urbana, Ill., evaluated rice hulls, leaf-waste pellets, and pine bark as herbicide carriers for the preemergence herbicides oryzalin at 2 lb/acre a.i. and diuron at 1 lb/acre a.i. The efficacy of the treatments in controlling annual weeds and the phytotoxic effects of the treatments on the woody plant species were evaluated in separate completely randomized designs. For the efficacy experiment, no ornamental plants were present and containers were each seeded with a mixture of 1:1:1 (by volume) of annual bluegrass (Poa annua), common groundsel (Senecio vulgaris), and shepherd's purse (Capsella bursa-pastoris) immediately after treatment applications. For the phytotoxicity experiment, ‘Goldflame’ spirea (Spiraea japonica), ‘Hetz Midget’ american arborvitae (Thuja occidentalis), and ‘Snowmound’ nippon spirea (Spiraea nipponica) were evaluated. No weed seeds were sown in the phytotoxicity containers. Treatments for both experiments included spray applications of herbicides with water or with one of the organic mulches as a carrier or one of the mulches alone. Evaluations were done 45 and 120 days after treatment (DAT) in both years. The organic carriers with herbicide sprays gave efficacy visual ratings equivalent to water as a carrier for both herbicides. Phytotoxicity was not observed in the spirea species in either year. For ‘Hetz Midget’ american arborvitae in 2002, diuron with water had the highest visual phytotoxicity rating. Diuron phytotoxicity on the ‘Hetz Midget’ american arborvitae was alleviated when diuron was applied with any of the three mulches as a carrier. Pine bark treatments increased plant biomass for ‘Goldflame’ spirea in 2003, 45 DAT. At 120 DAT in 2002, pine bark gave increased plant biomass as compared with no organic mulch treatments for ‘Goldflame’ spirea. The study was conducted to ascertain whether the use of organic mulches as carriers could reduce phytotoxic effects of a herbicide on container-grown woody ornamentals, improve crop plant biomass, and act as a herbicide carrier for container-grown woody ornamentals.

Weed control is the largest expense faced in the nursery and landscape industries. Nursery growers spend $967 to $2,228/A, depending on species, for supplemental hand weeding in addition to three to four yearly herbicide applications. Herbicide-treated mulches have utility in addressing many current nursery/landscape weed control issues such as non-target herbicide losses, leaching and off-site herbicide movement, and reduction of weed control costs. The objectives of this study were to compare seven types of mulches, including Douglas fir nuggets, pine nuggets, shredded hardwood, shredded Cypress, PennMulch™, rice hulls, and cocoa shells sprayed with Surflan [aqueous solution (AS) (oryzalin) at 1.12 (0.5×) and 2.24 (1×) kg ai/ha (1.0 and 2.0 lb ai/A)] and SureGuard [(water dispersible granular (WDG) (flumioxazin) at 0.19 (0.5×) and 0.38 (1×) kg ai/ha (0.17 and 0.34 lb ai/A)] to determine efficacy on common chickweed (Stellaria media), annual bluegrass (Poa annua) and spotted spurge (Chamaesyce humistrata) and phytotoxicity to Golden vicary privet (Ligustrum × vicaryi), creeping juniper (Juniperus horizontalis ‘P.C. Youngstown’), and wintergreen boxwood (Buxusmicrophylla ‘Wintergreen’) at 45 and 115 days after treatment (DAT). The herbicide-treated mulches were compared to untreated mulches, over-the-top sprays of the herbicides and a combination spray of Surflan + SureGuard each applied at the 1× rate, described above, an industry-standard granular formulation Rout (oxyfluorfen + oryzalin) at 3.41 kg ai/ha (3.0 lb ai/A), an industry standard nonchemical alternative Geodisc™, and an untreated control. The experiment was conducted in 2001 and repeated in 2002. In 2001, 17 of 43 treatments provided commercially acceptable visual ratings at 45 DAT; 14 were herbicide treated mulches. Four of five treatments in 2001 providing acceptable control at 115 DAT were herbicide treated mulches. In 2002, three treatments providing commercially acceptable control at 45 DAT were: PennMulch™ + 0.5 × Surflan, PennMulch™ + SureGuard, and Rout. Rout was the only treatment providing commercially acceptable control at 115 DAT in 2002. Golden vicary privet exhibited the greatest phytotoxicity in both years. In 2001-2002, the over-the-top sprays of Surflan + SureGuard were the most phytotoxic treatments to Golden vicary privet when averaged across 45 and 115 DAT. The data indicated a significant herbicide × mulch interaction and that some combinations, such as hardwood + SureGuard or pine nuggets + SureGuard, increased and extended efficacy and reduced phytotoxicity versus mulches or herbicides applied alone.