Research reported by Virginia Tech's Drs. Holly Scoggins and Robert Wright in the March/April 2001 issue of the VNLA Newsletter underscores our need to have a greater understanding of just what certain plants either need or tolerate in the way of fertilizer programs. If you look carefully at their numbers and compare them to what we have been seeking for most of the shrubs and trees we are growing in containers in North Carolina, it will also help us to understand why the same fertilizer program may be good for one plant and kill or damage another.

They were fertilizing with Scott's Excel 15-16-17 applied as a constant liquid feed (every watering) with a 20-30% leaching fraction to prevent build-up of salts. Their treatments were four rates of 50, 150, 250 and 350 mg/L (ppm) Nitrogen. Root zone pH and EC were measured weekly using the VTEM system we all seem to be using these days.

Guidelines for the perennials in their test are as follows:

• Low Fertility (150 ppm N) - EC (mS/cm) 0.75-2.00: Heuchera x 'Mt. St. Helen,' Physostegia virginica
• Moderate Fertility (250 ppm) - EC (mS/cm) 2.00-3.5: Astilbe chinensis, Campanula carpatica, Coreopsis verticillata, Perovskia atriplicifolia, Veronica x 'Goodness Grows'
• High Fertility (350 ppm) - EC (mS/cm) 3.5-5.0: Gaura lindheimera, Lamium maculatum, Penstemon x 'Sour Grapes,' Salvia nemerosa

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