The riskiest areas can be seen to include most of the northern portions of the state, especially in the western counties, with improving conditions toward Harford and Cecil Counties; and a ridge extending down through the center of the state, along the Carroll/Frederick, the Montgomery/Howard and the Prince Georges/Anne Arundel boarders. More moderate winter temperatures prevail along the Maryland/Delaware boarder and on either side of the Chesapeake Bay.
Topography plays a significant role in the quality and consistency of quality of wine grapes. In general, an elevation of 400 - 600 feet is best, with winter damage risk increasing with altitude (although by the same token the danger of early/late killing frosts decreases somewhat). Similarly, vineyards located on low pockets are vulnerable to frequent frosts. A gentle slope promotes good cold air drainage as long as there are no significant barriers to the flow. Steep slopes, however, pose problems for machinery and increase potential for erosion. A southern facing slope has the advantage of greater daily maximum temperatures and longer daily heating of fruit and vines. Fields which have been under crop cultivation in previous years offer the best potential for vineyard sites. Otherwise, the area should be cleared of large rocks, tree stumps, heavy brush, etc, then cultivated and planted in grass or grain for one or two years. Soil pH should be between 5.5 - 6.5, but can be adjusted by an application of lime (high pH soils are rare in Maryland).
Proximity to heavy woods can pose problems, as they harbor wildlife which feed on grapes or vine shoots -- deer and birds are the worst offenders. A number of measures are available for crop protection, none of them entirely satisfactory. Also, proximity to fields in which 2-4D is used as an herbicide is risky, as drift from this pesticide can be extremely injurious to grapevines.
Soil types and suitability range widely throughout the state. Fortunately, grapevines are tolerant of what might be considered risky areas for other crops. They are grown in soils ranging from heavy clay to sand to shale and rock. Ideally, the soil will be loamy (approx equal proportions of sand, silt and clay), deep (30 - 40 inches of permeability) and well-drained, with moderate fertility. Too much fertility can result in excessive vegetative growth, whereas mildly deficient soil can encourage the vines to extend their root systems to greater depths, often resulting in higher quality fruit.
Soils which tend to be waterlogged, shallow,
primarily heavy clay, hardpan (impervious subsoils which limit root penetration)
and excessively acidic should be avoided. Sandy soils provide good aeration
but have poor water retention, whereas clay soils have good water retention
and nutrient supplies but poor aeration.
Where feasible, deep tilling with a subsoiler
to a depth of at least 2' prior to planting can be beneficial.
The primary nutrients for grapevines are
nitrogen, phosphorus and potassium, and to a lesser extent boron, calcium
and magnesium. Soils severely deficient in any of these can be adjusted with
applications of appropriate fertilizers.
Adequate precipitation has never been a serious problem in Maryland. Vine roots are capable of growing to considerable depths in search of water and nutrients. The only exception is newly-planted vines which may suffer in drought conditions and may need to be irrigated.
The following chart lists the counties with established vineyards, the numbers of vines planted, and the approximate acreage in each.