Precision seeding. Hybrid seed is expensive. Precision seeding can significantly reduce costs by reducing the amount of seed needed because individual seeds are placed at a precise depth and spacing. In addition, precision seeding improves plant uniformity, which leads to better plant stands, uniform harvest (note, this is particularly important for once-over harvest), and increased yields. Also, the requirement for plant thinning is eliminated.

High-quality seed must be used along with proper land preparation to maximize the benefits of precision seeding. Sufficient moisture must also be provided for the planted seed. Good establishment practices must be carefully followed to assure a complete, uniform plant stand.

Belt, plate, and vacuum precision seeders are suitable for planting cucumbers. With belt seeders (e.g., Stanhay), circular holes are punched at intervals along a belt to achieve desired spacing. Pelleted seed (seeds encased in an inert material and made round for easy planting) should be used with belt planters to obtain better singulation (one seed as opposed to two or more seeds sown at a specific depth and distance apart). Although singulation is improved with pelleted seeds, they are bulky and cost more than seeds that have not received this treatment. Seeding is much slower with a belt seeder than with a plate or vacuum seeder; however, it is more accurate than a gravity feed seeder (e.g., Planet Jr.).

With plate-type seeders (e.g., John Deere 33), seed catch on a notch in the plate, then drop from the seed hopper to the ground. Spacing can be adjusted by gearing the rate at which the plate turns. Some precision is lost due to the long drop of the seed from the hopper to the ground.

A vacuum seeder (e.g., Stanhay, Monosem, Gaspardo, John Deere) provides very accurate precision seeding. The vacuum column holds a seed against a vertical plate with holes. When the vacuum is broken, the seed is dropped. The seeder employs various mechanisms to remove excess seed and drop one seed per vacuum hole (singulation). The number of holes per plate, as well as gearing, can be varied to achieve desired spacing. Spacing (plant population density) is most easily adjusted with this type of planter.

Plant Spacing/Population for
Hand-harvested Pickling and Slicing Cucumbers

Best plant spacing will vary considerably depending on harvest method and cultural practices (Table 5). Under conventional hand-harvest culture, row widths may vary from 30 to 48 inches (Table 6). Most prevalent are 36- to 42-inch rows with plants 6 to 8 inches apart in the row. With irrigation, regardless of row width, growers should strive for 30,000 plants per acre for pickling cucumbers and 25,000 plants per acre with slicing cucumbers. This will require approximately two pounds of seed per acre. Higher plant populations can sometimes result in plant stress due to inadequate nutrition and moisture. High plant populations can also result in short fruit with light color, and dense vine growth can make harvest difficult. Thinning, however, should only be done in extreme cases of overpopulation.

Table 5. Recommended Plant Population, Spacing, and Quantity of Seed for Multiple-hand Harvest on Bare Soil and Plastic-mulched Soil, and Once-over Machine Harvest on Bare Soil

Harvest/Culture	Plant Population 1,000/acre	Spacing (inches)		Seed lb/acre
		In-row	Between-row
Hand/Soil	25-30	5-10	30-48	2
Hand/Plastic	20-30            double row (18 inches            between rows on bed)	10-14	60	2
Machine/Soil	50-70	3-4	24-28	4-5

Table 6. Number of Plants per acre (in thousands) by between-row and in-row spacing

Between rows (inches)	------- In-row (inches) -------
	3	4	5	6	7	8	9	10
24	87.1	65.3	52.3	43.6	37.3	32.7	29.0	26.1
30	69.7	52.3	41.8	34.8	29.9	26.1	23.2	20.9
36	58.0	43.6	34.8	29.0	24.9	21.8	19.4	17.4
42	49.8	37.3	29.9	24.9	21.3	18.7	16.6	14.9
48	43.6	32.7	26.1	21.7	18.7	16.3	14.5	13.1

	= approximate recommended plant populations per acre for once-over machine harvest.
	= approximate recommended plant populations per acre on unmulched soil for hand harvest.

Plant Spacing/Population for Machine-harvested Pickling Cucumbers

For once-over (machine) harvest, recommended plant populations are much higher (50,000 to 70,000 plants per acre) than for multiple-hand harvest (Table 5). Rows are usually planted 24 to 28 inches apart (three rows per bed) with plants spaced 3 to 4 inches apart in-row.

General Considerations for Earliness

In most cases, little is gained by planting early in the spring, particularly for pickling cucumbers for which growers have a contract set price. The first harvest for pickling cucumbers in eastern North Carolina is usually June 1 to 5, while slicers are usually ready by June 10 to 15 if they are planted by mid-April. An early crop harvest might have a price advantage with fresh-market cucumbers for a short period of time. Special growing practices should be employed to achieve an early harvest.

Earliness for Fresh-market Pickling and Slicing Cucumbers

Early harvests can by achieved by use of containerized transplants, rye/wheat windbreaks, row covers, and plasticulture.

Transplants should only be considered if market considerations warrant (when profits exceed added transplant costs). Choose only containerized transplants with at least a 1.5-inch diameter cell size. Cucumbers are very sensitive to root disturbance so transplants should be handled very gently. Rough handling can result in severe stunting, thus losing the advantage of earliness. The use of transplants is not common due to the extreme sensitivity of cucumber transplants to rough handling.

Windbreaks, provided by seeding rye or wheat between every four to six rows in the fall, offer protection from cold prevailing winds and minimize sandblast injury to plants. Windbreaks also can improve earliness by reducing heat loss and plant injury and usually are not cut until about three to four weeks after seeding. Windbreaks can harbor aphids and thrips; growers should scout for these pests early in the season.

Row covers provide a warm microclimate and protection from light frost. However, they must be removed to allow bee flight and pollination. Black plastic, or infrared transmissible plastic, can be used for soil warming and weed control. When cucumbers are planted on plastic in early spring, generally 7 to 10 days earliness is gained.

Scheduling Harvest for Pickling and Slicing Cucumbers

Fig. 5. Average last frost dates. Adjust last frost dates according to distance from date lines.

Favorable planting conditions usually occur between April 10 and 20 in the coastal plain of North Carolina, between April 21 to 30 in the central Piedmont, and between May 1 to 15 in the mountains and foothills (Figure 5). For optimum yield before frost, seeding for the fall crop should be completed by August 5 in eastern North Carolina, July 25 in the central Piedmont, and mid-July in western North Carolina. For more specific weather and climate information for your location, refer to bulletin AG-375, Weather and Climate in North Carolina (Epperson et al. 1988).

Plantings should be carefully scheduled so that labor and machinery are used efficiently and harvests from each planting will not overlap. Scheduling harvests can also result in more timely production for higher price market windows.

A heat unit (HU) model (Perry and Wehner 1996) has been developed which better predicts cucumber harvest dates than the standard model. A ceiling of 90°F is used in the new model because cucumber plant growth stops or is inhibited above this temperature. To compute HUs for each day, get the maximum air temperature for each day, then use one of the following equations:

1. If maximum air temperature is 90°F or lower
   HUs = maximum temperature - 60°F
               or
   
2. If maximum air temperature is equal to or higher than 90°F
   HUs = [90-(maximum temperature - 90)] - 60

To use this model in North Carolina, growers must use tables of daily normal HU accumulation and the associated harvest dates. See Table 7 for a sample prepared for Clinton. To acquire the climatological data for your location, contact your county Extension center. Table 7 is designed for use with mid-season, pickling-type cultivars which have an HU target of 1,125. However, certain slicing and even some pickling-type cultivars may have different maturities. Thus, scheduling will need to be adjusted to HUs for a particular cultivar (Table 8).

Table 7. Predicted Heat Unit (HU) Accumulation, Harvest Date, and Total Days from Planting
to Harvest (DTH) for Pickling Cucumbers Planted in Clinton, N.C., from March 1 to September 2

Planting date HU Harvest date DTH Mar 1 149 May 2 81 2 155 2 80 3 161 2 79 4 168 22 79 5 175 22 78 6 182 22 77 7 186 22 76 8 192 23 76 9 198 23 75 10 202 23 74 11 209 23 73 12 216 24 73 13 225 24 72 14 237 25 72 15 247 25 71 16 256 25 70 17 262 26 70 18 266 26 69 19 273 26 68 20 281 27 68 21 290 27 67 22 297 27 66 23 301 28 66 24 308 28 65 25 315 28 64 26 322 29 64 27 328 29 63 28 337 29 62 29 346 30 62 30 358 30 61 31 370 3 61 Apr 1 384 3 60 2 397 Jun 1 60 3 412 1 59 4 428 2 59 5 443 3 59 6 454 3 58 7 465 3 57 8 476 4 57 9 486 4 56 10 495 5 56 11 506 5 55 12 521 6 55 13 537 6 54 14 552 7 54 15 567 8 54 16 583 8 53 17 596 9 53 18 609 9 52 19 624 10 52 20 641 10 51 21 657 11 51 22 673 12 51 23 690 12 50 24 707 13 50 25 723 14 50 26 739 14 49 27 755 15 49 28 774 16 49 29 791 16 48 30 807 17 48 May 1 825 18 48

Planting date HU Harvest date DTH 2 843 19 48 3 861 19 47 4 878 20 47 5 896 21 47 6 914 21 46 7 935 22 46 8 954 23 46 9 972 24 46 10 988 24 45 11 1,006 25 45 12 1,028 26 45 13 1,050 27 45 14 1,072 27 44 15 1,093 28 44 16 1,113 29 44 17 1,135 30 44 18 1,155 Jul 1 44 19 1,176 1 43 20 1,199 2 43 21 1,220 3 43 22 1,242 4 43 23 1,265 5 43 24 1,290 6 43 25 1,311 7 43 26 1,331 7 42 27 1,352 8 42 28 1,373 9 42 29 1,396 10 42 30 1,420 11 42 31 1,445 12 42 Jun 1 1,471 13 42 2 1,496 14 42 3 1,522 15 42 4 1,544 16 42 5 1,568 16 41 6 1,593 17 41 7 1,619 18 41 8 1,645 19 41 9 1,670 20 41 10 1,696 21 41 11 1,719 22 41 12 1,743 23 41 13 1,768 24 41 14 1,793 25 41 15 1,818 26 41 16 1,844 27 41 17 1,869 28 41 18 1,894 29 41 19 1,919 30 41 20 1,946 31 41 21 1,972 Aug 1 41 22 1,997 2 41 23 2,021 3 41 24 2,048 4 41 25 2,074 5 41 26 2,099 6 41 27 2,125 7 41 28 2,150 8 41 29 2,176 9 41 30 2,204 10 41 Jul 1 2,230 11 41 2 2,256 12 41

Planting date HU Harvest date DTH 3 2,282 13 41 4 2,308 14 41 5 2,335 15 41 6 2,360 16 41 7 2,386 17 41 8 2,412 18 41 9 2,438 19 41 10 2,464 20 41 11 2,490 21 41 12 2,516 22 41 13 2,542 23 41 14 2,569 24 41 15 2,595 25 41 16 2,621 26 41 17 2,647 27 41 18 2,674 28 41 19 2,701 29 41 20 2,727 30 41 21 2,752 31 41 22 2,777 Sep 1 41 23 2,802 2 41 24 2,829 3 41 25 2,855 4 41 26 2,883 5 41 27 2,909 6 41 28 2,936 7 41 29 2,962 9 42 30 2,988 10 42 31 3,015 11 42 Aug 1 3,041 12 42 2 3,068 13 42 3 3,095 14 42 4 3,121 15 42 5 3,147 16 42 6 3,173 17 42 7 3,200 19 43 8 3,227 20 43 9 3,253 21 43 10 3,280 22 43 11 3,305 23 43 12 3,331 24 43 13 3,357 26 44 14 3,384 27 44 15 3,409 28 44 16 3,436 29 44 17 3,462 Oct 1 45 18 3,487 2 45 19 3,512 4 46 20 3,536 5 46 21 3,561 6 46 22 3,587 8 47 23 3,610 10 48 24 3,637 11 48 25 3,662 13 49 26 3,688 15 50 27 3,716 17 51 28 3,742 19 52 29 3,768 21 53 30 3,794 23 54 31 3,818 25 55 Sep 1 3,842 27 56 2 3,868 29 57

Table 8. Target Heat Unit (HU) Accumulation from Planting to First
Harvest for Pickling and Slicing Cucumber Cultivars

Pickling Cucumber Cultivars Early Season Maturing HU = 1,053 Midseason Maturing HU = 1,125 Blitz Panorama Clinton Calico Pikmaster Pennant Calypso Pinnacle Saladin Carolina Regal SMR 58 Cascade Reliance Sumter Castlepik Salvo Triple Pak Chemset Sampson Wisconsin SMR 18 Commander Score   Earlipik 14 Southern Belle   Explorer Tamor   Fremont Target   Greenpak Tempo   Gynomite Totem   Lucky Strike Triple Crown   Medusa Triplemech   Multipik

Slicing Cucumber Cultivars Early Season Maturing HU = 1,154 Midseason Maturing HU= 1,246 Late Season Maturing HU = 1,337 Lama Dasher II Ashley Raider Castlemaster Comanche 7 Revenue Centurion Early Triumph Slice King Cherokee 7 Marketmore 76 Slice Nice Coolgreen Marketsett Slicemaster Guardian Pacer Sprint 440 Jet Set Poinmarket   Medalist Poinsett 76   Slice Mor Slice   Verino Super Slice


Note: Some cultivars may no longer be available, but can be used to determine heat units to harvest for similar or related cultivars.

The following procedure enables the user to update harvest prediction based on daily observed air temperatures:

1. Calculate HUs for each day using equations 1 and 2 above.
2. Keep a running total of these HUs beginning on the planting date.
3. Update the harvest prediction date by subtracting the current total from 1,125. Add the result to the accumulated HUs from the table for the current day. Find the number closest to this result in the HU column of Table 7 to determine the associated harvest date.

Example of harvest scheduling
Planting date is April 10 at the Clinton location. At planting, the initial predicted harvest date is June 5, which assumes the average weather conditions on which the table is based.

When summing HUs accumulated by April 25 using steps 1 and 2 above, it is determined that 400 HUs have accumulated. This is substantially more than an average year, thus the predicted harvest date would change. Normally, the total HUs accumulated would be 723 - 495 = 228. (Note, the amount accumulated from March 1 to April 10 must be subtracted to determine the units accumulated for April 11- 25.)

1. 1,125 - 400 = 725
2. 723 + 725 = 1,448
3. Closest number to 1,448 is 1,445
4. Updated harvest date prediction is May 31 (Note: When using the table to update your prediction, use the planting date column.)

Scheduling is especially critical if once-over machine harvest is used because the harvest window is usually only one to two days for highest yield and profit. (See the Machine Harvest section for more detailed information.) Mechanical harvesters can ony harvest about 10 acres a day, so if large acreages are being grown, they must be scheduled carefully to allow time for each separate acreage to be harvested. For example, for mechanical harvest, about 25 HUs accumulated between spring plantings leaves one day between harvests provided that best cultural practices are followed. Approximately 300 HUs are needed to accumulate between spring plantings to space beginning harvests about 14 days apart, whereas about 500 HUs are required for beginning harvests for each planting to be about 21 days apart. Planting such that harvest intervals are two to three weeks apart will help to maintain a continuous supply of good-yielding hand-harvested cucumbers. Use Table 7 and the example above to predict harvest for mid- to late-summer plantings as daily HUs become more variable late in the growing season.

Cultural Management, continued

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Crops      Commercial Horticulture