Growing Greenhouse Tomato Transplants

Although transplants may be purchased, most growers produce their own to insure that healthy plants are available when needed.  Fall crops are generally seeded in late July through early August, while winter crops are sown toward the end of November.  When plants are approximately 4 weeks old (at least 1 week before the first flower opens) they are transplanted into beds, troughs, bags, etc.

One ounce of tomato seed contains approximately 9,000-12,000 seed and, with standard germination, this should be sufficient to produce 6,000-9,000 healthy plants.  It is also a good idea to grow about 20% more plants than needed to insure quality.  The cost of  žgoodÓ seed is insignificant compared to other costs of growing a crop and recommended varieties should be used.  Prior to planting, seed may be treated with a fungicide to prevent losses from damping off.

The germination media used is extremely important in producing transplants.  In general, this media should be fine in texture (to provide good seed to media contact) with adequate water holding capacity.  It is also important that the media be free from pathogens that may cause seed deterioration.  In general, 2:1 combinations of peat and vermiculite or peat and sand make an excellent germination media.

Seed should be sown in a flat or tray 1/4 inch deep.  The seed is then lightly watered in and moisture level is kept high during the germination period.  Flats can be covered with grass or plastic to prevent water loss.  The growing media should be kept at 75 degrees to 85 degrees F.

When plants have sprouted and developed their first set of true leaves, they should be transplanted into packs or small pots  (i.e. 2 1/4" - 4").  Daytime temperatures should be maintained at 70 degrees to 80 degrees F and 60 degrees to 65 degrees F for nights.  Fertilize plants each week with a complete, soluble fertilizer at ½ strength.

Transplanting Into Beds, Troughs, etc.

Transplants should be set in the media 1" deeper than they were previously grown.  If transplants are tall and spindly, set them on their sides in a shallow trench allowing 6" to 8" of the shoot to extend above the soil.

The number of plants needed will depend on row and plant spacing.  A recommended plant spacing in soil is 18 inches between plants and about 36 inches between rows.  This spacing allows approximately 4.5 square feet per plant.  One may grow as close as 3 ½ feet per plant.  In an average 30'x100' greenhouse using the recommended plant spacing and beginning the first row three feet away from the side, approximately 540 plants will be required (9,680 plants/acre).  The plant spacing in the row for various row widths to provide about 10,000 plants per acre is given in the following table:

Plant Spacing in Row
Row Width
21 30
19.5 32
18.5 34
17.5 36
16.5 38
15.5 40
16 39
18 35
20 31
22 28.5

To use the table for variable row spacings, average the row widths and use this average for determining the plant spacing in the row.  For example; many growers prefer an average row spacing of 36 inches by alternating 40 inch rows with 32 inch rows.  The plant spacing from the table for 36 inch rows is 17.5 inches for about 10,000 plants per acre (actually 9,956 plants per acre).  In soil, a fall crop population should run 9,500 to 10,000 plants per acre.  The spring crop population could be boosted by about 10%.  Remember that higher populations mean greater risk from plant pests and greater attention to the plants.

Another scheme (Figure 1) allows an extra row of plants by utilizing five double-row beds for this same sized house.  Each bed is 42 inches wide with 18" service aisles.  Planting 18 inches within the row and staggering or offsetting rows within a bed would require about 590 plants (11,422 plants per acre).  Rows should be about 20 inches apart in bed.

The scheme in Figure 1 is a high density population and should only be considered by an experienced grower.  Fertilizer should be increased accordingly.

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