Samples of seven controlled-release fertilizers, Nutricote Total 13 -13 -13, Nutricote Total 18 -6 -8, Osmocote Plus 15 -9 -12, Osmocote 13 -13 -13, Polyon 18 -6-12, Polyon 14 -14 -14, and Plantacote 14 -8 -15, were placed in leaching columns containing acid-washed sand. Samples of all leachates were analyzed weekly to determine release rates of ammonium-nitrogen (N), nitrate-N, phosphorus (P), potassium (K), magnesium (Mg), manganese (Mn), and iron (Fe). Release rates for P from all products were slower than those for NH 4 -N, NO 3 -N, and K. Release of Mg, Mn, and Fe was very poor, with less than 50% of the total amount of each of these elements ever being released from the prills for some products. Nutricote products released Fe and Mn more effectively than did Osmocote or Plantacote.

The ornamental horticulture industry uses a variety of materials as ingredients in growing substrates for many ornamental plants. There are many attributes that make growing substrates effective, including good aeration and drainage, availability at an acceptable price, and chemical attributes conducive for plant growth. In recent years there has been a trend in which more traditional organic components, such as Canadian sphagnum peat, have been partially replaced by an increasing array of waste-product compost. Plant response to increasing quantities of compost in the potting mix, and to different types of compost are variable. This paper reviews some important issues in the utilization of urban waste compost products.

In two experiments, chinese hibiscus (Hibiscus rosa-sinensis), bamboo palm (Chamaedorea seifrizii), areca palm (Dypsis lutescens), fishtail palm (Caryota mitis), macarthur palm (Ptychosperma macarthurii), shooting star (Pseuderanthemum laxiflorum), downy jasmine (Jasminum multiflorum), plumbago (Plumbago auriculata), alexandra palm (Archontophoenix alexandrae), and foxtail palm (Wodyetia bifurcata) were transplanted into 6.2-L (2-gal) containers. They were fertilized with Osmocote Plus 15N-3.9P-10K (12-to14-month formulation) (Expt. 1) or Nutricote Total 18N-2.6P-6.7K (type 360) (Expt. 2) applied by either top dressing, substrate incorporation, or layering the fertilizer just below the transplanted root ball. Shoot dry weight, plant color, root dry weights in the upper and lower halves of the root ball, and weed shoot dry weight were determined when each species reached marketable size. Optimal fertilizer placement method varied among the species tested. With the exception of areca palm, none of the species tested grew best with incorporated fertilizer. Root dry weights in the lower half of the root ball for chinese hibiscus, bamboo palm, and downy jasmine were greatest when the fertilizer was layered and root dry weights in the upper half of the root ball were greatest for top-dressed chinese hibiscus. Weed growth was lower in pots receiving layered fertilizer for four of the six palm species tested.

Zonal geraniums (Pelargonium ×hortorum) from seed and african marigolds (Tagetes erecta), which are known to be highly susceptible to Fe toxicity problems, were grown with I, 2, 4, or 6 mm Fe from ferrous sulfate, ferric citrate, FeEDTA, FeDTPA, FeEDDHA, ferric glucoheptonate, or ferrous ammonium sulfate in the subirrigation solution. FeEDTA and FeDTPA were highly toxic to both species, even at the 1 mm rate. Ferrous sulfate and ferrous ammonium sulfate caused no visible toxicity symptoms on marigolds, but did reduce dry weights with increasing Fe concentrations. Both materials were slightly to moderately toxic on zonal geraniums. FeEDDHA was only mildly toxic at the 1 mm concentration on both species, but was moderately toxic at the 2 and 4 mm concentrations. Substrate pH was generally negatively correlated with geranium dry weight and visible phytotoxicity ratings, with the least toxic materials, ferrous sulfate and ferrous ammonium sulfate, resulting in the lowest substrate pHs and the chelates FeEDTA, FeDTPA, and FeEDDHA the highest pH. The ionic Fe sources, ferrous sulfate and ferrous ammonium sulfate, suppressed P uptake in both species, whereas the Fe chelates did not. Fe EDDHA should be considered as an effective and less toxic alternative for the widely used FeEDTA and FeDTPA in the production of these crops.