Planting depth and spacing - To provide winter protection and to reduce mechanical damage in the site, most flower bulbs must be planted either 5 inches (12.5 cm) or 8 inches (20 cm) deep to the base of the bulb (Table 1). For these bulbs, two systems are available to accomplish this. There are, however, many bulbs that should be covered with only 1 to 2 inches (2.5-5 cm) of soil (Table 1).

• Conventional planting system - This system requires that the planting area be dug out to the required planting depth for the bulbs. Subsequently, the bulbs are spaced properly (Table 1) and then covered with the removed soil. Since a mulch of 2 to 3 inches (5-7 cm) is advised, this amount should be calculated in the planting depth.
• Modified mulching system - In recent years, a planting system using pine bark mulch has been developed for heavy, poorly drained soils. In this system, the site is rototilled 4 inches (10 cm) deep, the bulbs are spaced properly (Table 1) and they are subsequently covered with 5 to 8 inches (12.5-20 cm) of 1/2 inch screened pine bark mulch amended with lime at the rate of 5 pounds/cubic yard. The mulch provides winter protection. This system also takes into consideration that most flower bulbs produce contractile roots. These roots will position the bulbs at the optimal depth for subsequent growth and development.

Planting Dates

Some late spring and early summer flowering bulbs. Generally, these bulbs must be planted in the fall (Table 1) in order to develop a good root system and to satisfy the cold requirement of the specific species. The cold ranges from 6 to 20 weeks depending on the species and/or cultivar. The exact time to plant these bulbs depends on the prevailing soil temperature. In general, it is best to wait until the soil temperature is below 60°F (16°C) at the optimal planting depth. The basic planting periods for planning purposes are as follows:

Climatic Zone	Optimum Planting Period
3	September
4 and 5	September to early October
6	October
7 and 8	November to early December
9	Late November to early December
10	December (primarily precooled bulbs)

Most Summer and fall flowering bulbs. Most summer and fall flowering bulbs are planted in the spring after the period for late spring frosts has passed.

Interplanting bulb types - When the garden design is created using two or more bulbs in the same site, be certain to plant the large bulbs at the 8 inch (20 cm) depth and the small bulbs at the 5 inch (12.5 cm) depth. They should be spaced properly at both depths based on the garden design.

Moisture and mulches - To properly root and grow, most flower bulbs require a soil that is moist, but not wet. Thus, consideration must be given to conserving soil moisture, especially during periods of drought. Therefore, it is advisable to use 2 to 3 inches (5-7 cm) of an organic mulch after planting. Mulch also aids in providing protection against extreme cold and heat and in controlling weeds. In addition, supplemental watering s may be necessary during long periods of drought.

Support System - Many of the tall growing plants, e.g., Dahlias and Lilies, may require a support system to prevent them from being affected by severe winds and rains. These systems should be installed either at planting time or shortly thereafter.

Approximate Planting Density (bulbs per square foot) Chart for Flower Bulbs

Bulb Size (cm, in circumference)	Spacing (inches) between bulbs
	0	0.5	1	2	3	4	5	6	7	8	9	10	11	12
4/5	500	150	60	-	-	-	-	-	-	-	-	-	-	-
5/6	350	100	50	25	-	-	-	-	-	-	-	-	-	-
6/7	225	80	40	25	10	-	-	-	-	-	-	-	-	-
7/8	175	80	35	20	10	-	-	-	-	-	-	-	-	-
8/9	125	60	35	15	-	-	-	-	-	-	-	-	-	-
9/10	100	-	25	15	-	-	-	-	-	-	-	-	-	-
10/11	75	-	20	15	-	-	-	-	-	-	-	-	-	-
11/12	65	-	20	12	-	-	-	-	-	-	-	-	-	-
12/14	50	-	15	10	-	-	-	-	-	-	-	-	-	-
14/16	35	-	-	10	-	-	-	-	-	-	-	-	-	-
16/18	25	-	-	10	-	-	-	-	-	-	-	-	-	-
18/20	25	-	-	10	-	-	-	-	-	-	-	-	-	-
20/24	-	-	-	8	6	-	4	-	-	-	-	-	-	1
24/30	-	-	-	-	-	-	4	-	-	-	-	-	-	1
30/up	-	-	-	-	-	-	3	-	-	-	-	-	-	1