Basil

Introduction

Basil (Ocimum spp.) is a member of the mint family. There are several species and numerous interspecific hybrids. The most common culinary type is sweet basil, O. basilicum, which also has purple and lemon-scented cultivars. Specialty types include Thai (O. tenuiflorum), lemon (O. americanum x O. citridorum) and small-leaved bush types of various species and crosses. Basil seed is not always true to type. Try to obtain high-quality seed that is uniform with a high germination percentage.

Types and Varieties

Basil Varieties
Sweet Purple
Amazel - BDM Red Rubin - BDM
Aroma 2 - F Dark Opal
Everleaf - BDM, F (intermediate) Amethyst Improved
Evi - BDM Prospera Red - BDM
Eleonora  - BDM  
Genovese Thai
Italian Large Leaf Sweet Thai
Newton - F  
Nufar - F Bush
Prospera - BDM Spicy Bush
Prospera Active - BDM Spicy Globe
Rutgers Devotion - BDM  
Rutgers Obsession - BDM, F Scented
Rutgers Passion - BDM Sweet Dani (lemon) - BDM
Rutgers Thunderstruck - BDM Lime Basil - BDM
  Holy Basil (medicinal)
  Cinnamon Basil
F: Some resistance to Fusarium wilt, BDM: Some resistance to basil downy mildew.

NOTE:  Basil downy mildew (Peronospora belbarhii) was first reported in the United States in 2007. Eleonora and Everleaf were the first downy mildew resistant sweet basil cultivars available in the US. Varieties with stronger resistance have since been released: Prospera, Amazel, and the Rutgers varieties Obsession, Devotion, Passion, and Thunderstruck. Thai, lemon, and spice basil varieties have intermediate BDM resistance.

Soil Fertility

Basil grows well in a warm, well-drained soil in a wide pH range, although the typical vegetable crop range of pH 6.0-6.8 is ideal. Although adequate fertility is required (see Table below), excess nitrogen applications can cause post-harvest discoloration and reduce flavor. Basil benefits from a sidedress application of nitrogen after the first or second cutting.

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR BASIL

BASIL

NITROGEN (N)* LBS PER ACRE

   PHOSPHORUS (P) LBS P2O5   PER ACRE

   POTASSIUM (K) LBS K2O      PER ACRE

SOIL TEST RESULTS

 

VERY LOW

LOW

OPTIMUM

ABOVE OPTIMUM

VERY LOW

LOW

OPTIMUM

ABOVE OPTIMUM

Broadcast and Incorporate

100

120

60

30

0

100

50

25-50

0

Sidedress after 1st or 2nd cutting

15-30

0

0

0

0

0

0

0

0

TOTAL RECOMMENDED

115-130

120

60

30

0

100

50

25-50

0

*SEE PLANT NUTRIENTS FOR INFORMATION ON NUTRIENT MANAGEMENT AND APPLICATION.

Planting

In New England, basil is most commonly transplanted, but because it is highly sensitive to cold (low 40s), it should not be set out until after danger of frost. Seeds will germinate within 4-8 days at temperatures of 68-74ºF. Transplant at approximately 6 weeks old. Topping when plants are 5-6 in. tall encourages branching. Basil is often spaced at 6-12 in. between plants in double rows. Tighter spacing will promote longer shoots for bunching.

If field soils are warm enough, basil can be direct-seeded in a well-prepared seedbed at a spacing of 8-10 seeds per foot and later thinned. Basil can be direct sown using an onion seeder. Pelleted seeds are also available to facilitate outdoor seeding.

Field Culture

Because of the lack of herbicides for weed control and the need for warm temperatures, basil is well suited to growing in raised beds covered with black plastic mulch. Drip irrigation allows consistent application of water while also reducing foliar diseases. Cultural management of insects, diseases and weeds is necessary because few pesticides are registered for use on basil.  Summer weight row covers can help to exclude insect pests but create a more humid environment that is more conducive to downy mildew development. Row cover is not required for production in mid-summer. However, high humidity is conducive to downy mildew, the most important pest of basil in recent years.

Harvest and Storage

Basil can be lightly harvested by pruning as early as 6 weeks after planting, with regular harvests starting a few weeks after that. Harvests should take place in the morning after the dew has left the plants. Depending on the intended use and market, individual leaves or entire stems may be harvested. Basil grown for culinary use should be harvested before flowering, as flavor will be adversely affected if plants are allowed to flower. If grown for essential oil production, basil should be harvested at full bloom. Plants will set seed if flower spikes are not removed as they appear. Sequential plantings can help ensure continuous production of quality shoots and leaves. Plan to finish harvesting downy mildew-susceptible varieties before mid-summer; resistant varieties can be expected to produce clean growth for a few weeks after downy mildew arrives.

Damage can be caused by rough handling, desiccation, and chilling (<40°F). Cooling can be accomplished by rinsing in 55°F water, but foliage should be dried completely prior to packing. Maintenance of clean growing conditions, free from mud splash, enables some growers to avoid contact with water. Basil should then be stored at temperatures above 54°F.