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.

Varieties

Basil Varieties  
Sweet/Pesto Purple
Genovese Red Rubin - BDM
Italian Large Leaf Magical Michael
Nufar - F Osmin Purple
Aroma 2 - F Purple Ruffles
Dolce Fresca Dark Opal
Eleonora  - BDM tolerant  
  Scented
Thai Sweet Dani (lemon) - BDM
Queenette - BDM Lime Basil - BDM
Thai Magic Holy Basil (medicinal)
Siam Queen Blue Spice - BDM
Sweet Thai Blue Spice Fil - BDM
  Spice - BDM
Bush  
Spicy Globe  
Spicy Bush  

Resistant or tolerant to: F: Fusarium wilt, BDM: Basil downy mildew (SEE BELOW).

Note: Basil downy mildew (Pernospora belbarhii) is a new disease in the United States and was first reported in 2007. Recent work in NY and NJ demonstrated strong susceptibility in the popular O. basilicum cultivars: Aroma 2, Genovese, Martina, Italian Large Leaf, Magical Michael, Nufar, Opal Purple Variegated, Poppy Joes, Queenette, and Superbo. No symptoms were found on leaves of Spice, Blue Spice and Blue Spice Fil. In an evaluation conducted on Long Island in 2009, Cinnamon, Queenette (Thai basil) and Red Rubin were less severely affected than Superbo.  A newly released sweet/pesto variety, Eleonora, has “intermediate” resistance to BDM because of the cupped leaf shape, but it still can get the disease.

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 four to eight days at temperatures of 65° to 80°F, with an optimum of 770F. Transplants should be 4 to 6 weeks old. Topping when plants are 5" to 6" tall encourages branching. Basil is often spaced at 6" to 12" 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 to 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 and create a more humid, tropical environment that is reminiscent of basil's native South Asian habitat. Some growers say that basil is more fragrant when grown in a wind-protected environment. 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. Flavor will be adversely affected if allowed to flower. If grown for essential oil production, it 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. However, harvesting basil by mid-summer can often prevent crop destruction from downy mildew.

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.