As a general rule, temperatures reach the level for safe planting of cool season crops about March 15 in southernmost States of the Northeast region. The northward progression of safe planting dates is about 5 to 7 days later for each 100 miles. In southern mountainous areas, cool season crop plantings can begin April 1. The Planting season progresses northward 5 to 7 days later per 100 miles.

Warm season crops can safely be Planted April 15 in southernmost States of the region. The season progresses northward with a delay of 5 to 7 days per 100 miles. Mountain areas need to delay an additional 5 to 10 days, starting after April 20 in the South.

Cool-season crops begin biological growth around 40 F and warm season crops begin growth around 50 . Cool season crops include asparagus, broccoli, brussel sprouts, cabbage, chives, collards, kale, kohlrabi, rutabaga, spinach, turnip, beet, carrot, cauliflower, celery, endive, lettuce, parsnips, potato, and salsify. Warm season crops include snapbean, sweet corn, tomato, most vine crops, eggplant, lima bean, pepper, melons, and sweet potato. Tree fruit and small fruit are included in cool season crops.

Average length of the frost-free growing season ranges from 180 to 234 days in the south and from 90 to 120 days in the north and mountainous areas.

The growing season rainfall March through October varies from 20 inches in the west to 40 inches in the south and east. Rainfall is the least in September through October and the greatest in June. Summer rainfall comes mainly from thunderstorm activity and often is poorly distributed during July and August. Dry, hot periods lasting 2 to 3 weeks are common during midsummer through the Northeast. In these periods warm season crops, double crop plantings, and tree fruit often suffer from stress and require supplemental irrigation to survive.

Extensive wet periods often occur in late May and June. Cool wet periods in April delay planting and establishing gardens with a frequency of 2 or 3 years in 10 years. These wet periods produce seed rot and disease problems.

Evaporation and transpiration may exceed precipitation during July through September, and in July may reach a 2 to 1 ratio.

Climate effects must be considered in handling garden soils. Garden crops have a limited root system and require a continuous supply of nutrients and moisture. Excessive rainfall leaches out soluble nutrients and increases acidity. Wetness causes aeration problems and poor root growth.

Climate and soil texture are important for soil warm-up in spring. Sandy soils warm earliest and have the widest daily variation. Heavy soils are cool in spring, warm slowly, and hold heat longer in autumn. Soil temperature at planting depth usually exceeds the air temperature by 5 to 10 F during the afternoon, and cools to several degrees lower than the air temperature at night. Soil temperature variations are largest when the soil is dry and smallest when it is wet.

Plant growth limitation occurs at various temperature thresholds. Temperatures above 86 F stop the growth of warm season plants, while temperatures as low as 77 halt the growth of cool season crops. Such temperatures occur as frequently as 10 days per month during summer in southern areas, and 2 to 3 days per month in the north. Warm season crops have lower growth limits around 50 and leaf tissue is killed at 30 to 31 . Cool season crops have a wider low temperature tolerance and some may withstand temperatures down to 20 before the leaf tissue dies.

Effects of the small scale climate close to the soil surface or near the crop canopy are important in gardening. Temperatures at the soil surface may be 20 to 40 F higher than the air temperature on hot, dry, sunny days and 5 to 10 cooler than air temperatures at night. Leaf temperature variations are 2 to 3 above air temperature on sunny afternoons and 1 to 2 cooler at night.

During low temperature periods, differences between forecast and surface level temperatures are important. Local forecasts predict what the temperature is expected to be at eye-level height of about 5 feet. Surface temperatures can be 2 to 8 F cooler on calm clear nights. Freezing temperatures down at crop level are possible with forecast temperatures of 35 to 40 F.

Direction of slope of the garden area is important. Southeast, south and southwest sloping surfaces are warmer, receive more solar radiation and dry out faster This may permit planting a week or more early. Gardens in low depression areas surrounded by high terrain are subject to cold air drainage and more frequent frost-freeze problems.

Freeze protection for garden plants is a necessity in the Northeast. In winter, perennial garden crops need protection from freeze-thaw action of the soil and protection from extremely cold soil temperatures. Straw mulches are effective.

Soil freeze depths in the Northeast range from 2 inches to over 24 inches, depending on snow cover. Root tissue damage develops at soil temperatures of 15 to 20 F.

During spring, protection by covering or by sprinkling on potential freeze nights pays dividends. Sprinkling is highly beneficial, particularly on dry cool nights when evaporative cooling causes leaves to super-cool. Sprinkling must begin a few degrees above freezing, and continue until all ice has melted and the temperature is several degrees above freezing.

Sprinkling prior to covering is effective during dry cold periods. This reduces radiation losses through plastic Covers.

Many crop management techniques can modify the local climate to reduce weather stress. Some are mulching, minimum tillage, plant population adjustment, shading, increasing organic matter, and adjusting fertility.