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Tomatoes

Annual outdoors, perennial indoors. Harvest summer onward

Tips for Planting

  • Tomatoes require a long growing season to mature and must be transplanted in the Prairie garden.  Tomato transplants can be grown from seed in your own home or purchased from a local greenhouse.
  • Whether you purchase or grow your own, your tomato transplant should be 20-25cm tall, dark green in colour, possess a strong, thick stem and not be root bound. 

Starting your own tomato transplants from seed:

  • Start transplants indoors at least 6 weeks prior to planting out.
  • Sow seeds 0.5cm deep in a commercial soilless media containing peat moss, perlite and vermiculite (ex. Sunshine Mix #4).  Soilless media provides a disease-free environment as well as excellent drainage to minimize root disease problems.
  • Use flats, pots or containers with bottom drainage holes.  At a soil or media temperature of 24˚C, tomato seeds should germinate within 6 days.
  • The biggest threat to the developing seed and seedling is a disease known as damping off (caused by a combination of several fungi; Phytophthora spp., Pythium spp., Rhizoctonia solani Kühn).  Damping off can be prevented by using soilless media, sowing seeds thinly, avoid overwatering, bottom watering, providing good lighting and setting up a floor fan several meters away to increase air circulation.  Never allow seedlings to sit in standing water.
  • Lighting: Good lighting is crucial for growth of healthy tomato seedlings.  To test if you have sufficient lighting:  the shadow cast on a white piece of paper at midday by an object 10-15cm above the paper should have a definite outline.  If there is no outline, light is inadequate and plants will stretch toward light, becoming pale and leggy.  A set of fluorescent tubes (one cool white and one warm white) placed 30-45 cm above the seedlings for 10-12 hours during the day will provide adequate light. 
  • Controlling Transplant Size: The ideal transplant has a good root system but is not root bound (tight, hard ball of roots that will not break up).  The stem will be strong. And the internodes will be small.  Transplants that are too tall will tend to break and dry out more easily once planted out into the garden.  Research has shown that stem diameter can be increased, and height controlled, by providing seedlings with constant air movement with an oscillating fan – or by lightly brushing seedling tops with tea towel or stick at least 20 times daily. 
  • Fertilize developing transplants two times/week using 20-20-20 water-soluble fertilizer.  Mix according to label directions.

Hardening off your tomato transplants

  • Moving tomato transplants from your home or the local greenhouse directly to the cold and often harsh reality of a prairie garden can result in stunted growth or even death.  “Hardening off” is the term used to gradually acclimatize your seedlings to the real world.
  • At least one week before transplanting out, place transplants outdoors in a sunny, protected location where the temperature is at least 15˚C. Bring transplants indoors over night for the first couple of days.  If temperatures are above freezing, leave transplants outdoors overnight in a protected location (i.e. next to a building or in an unheated building)  Transplants should be left outdoors at least three nights before transplanting into the garden.
  • Reduce watering and plant protection as the week continues.
  • Do not transplant tomato plants out until all danger of frost has passed (the traditional “average day of the last spring frost” in the Saskatoon area is typically May 24st).  Tomato plants are very sensitive to frost damage, so be prepared to protect plants with covers or blankets in the event of late spring/early summer frosts.

 Transplanting

  • Tomatoes prefer sandy loam, loam or clay loam soils for good fruit production.
  • Prepare the garden soil well in advance, adding organic matter and compost if needed.  The soil should be of good tilth: soft, crumbly and easily worked. 
  • When planting, cover the entire transplant “plug” or seed ball with soil to prevent the plant from drying out.  Exposed peat within the plug will act as a wick, drawing water away from the transplant and drying out the root ball.
  • Gently massage the roots within the plug so that the roots will grow into the surrounding soil and not remain restricted within the ball.
  • Ideally, transplanting should be done on a cool, cloudy day; hot, windy days will easily desiccate tender transplants.
  • Plant tomato transplants so that the lower part of the stem, up to the first set of leaves is covered with soil.  Avoid planting into deep, cooler soil.  For longer, larger transplants, plant the root ball and lower stem in a horizontal position; allowing existing roots to remain in the warm upper layer of the soil while encouraging root development along the buried stem.
  • Tomatoes should be planted at 45 cm spacings within the row, allowing at least 1m between rows.  Water-in the transplants will a starter fertilizer higher in phosphorous for good root growth (ex. 10-52-10)  Mix according to label directions.
  • For extra protection for your newly planted tomato transplants, place tin cans or milk cartons with the tops and bottom removed around newly planted tomatoes and insert them several centimetres into the soil.  Not only does this provide some wind protection and increase soil temperature, but it may also discourage cut worms.
  • For those gardeners that want to get an early jump on the growing season, warm up the soil with ‘Wall O’ Water’®: a series of plastic tubes filled with water joined together to form a wall of water around the transplant.  ‘Wall O’ Water’® have been known to protect plants to -11˚C.  Tomato transplants could be planted out at least 2 weeks earlier on the Prairies provided the soil under the ‘Wall O’ Water’® has also been warmed.

 Recommended Growing Conditions and Practices

  • Although tomatoes produce well in fertile soils, too much nitrogen, especially early in the season, will encourage excessive top growth and delay flowering and fruit production.
  • Tomatoes are a ‘warm season crop’.  This means they prefer warm temperatures and very sunny conditions for optimal growth. Tomatoes will benefit from planting in black, clear or dark green plastic mulch.  The mulch increases soil temperature as well as conserving soil moisture and suppressing weed growth.  Crop covers or clear plastic tunnels during the day are not recommended for tomatoes; the covers tend to encourage foliar growth and delay flowering and fruiting.
  • Tomatoes benefit from a steady supply of soil moisture.  Uneven watering, i.e. excessive water followed by drought conditions can disrupt the amount of calcium available in the plant for cell production.  This lack of calcium will result in physiological problems in the plant and tomato fruit.  Irrigate actively growing tomato plants with 2.5 cm water/week.
  • tomatoes should be staked or caged.  Cages and stakes expose the plant to more sunlight while keeping the fruit off the soil.     

Tomato Cultivars – How do I Decide?

  • Factors to consider when deciding what tomato cultivar to grow include; taste, days to maturity, end use, fruit size, plant size and type, disease resistance and availability.
  • Tomatoes that require more than ’70 days to maturity’ will probably not mature during an average Saskatchewan growing season.
  • If tomato diseases have been a big problem in your tomato garden in the past, look for disease-resistant tomato cultivars.  Most seed catalogues will indicate resistant cultivars.  

Determinate vs Indeterminate tomato plants

  • “Determinate” tomatoes bloom and produce fruit at nearly every node but are limited in growth.  Determinate tomatoes eventually terminate in one final flower cluster.  “Indeterminate” tomatoes produce flower clusters at about every third node but will continue to grow and produce fruit indefinitely.  Indeterminate plants must be pruned and staked for successful fruit production.  Determinate tomato plants are rarely pruned except near the end of the season to help existing fruit ripen on the vine.   Determinate tomato cultivars tend to ripen earlier than indeterminate tomato cultivars and therefore are preferred for Prairie gardens.

  • Indeterminate tomatoes must be pruned weekly. At each node, a sucker (or new shoot) will develop between the leaf cluster and the main branch. In order to produce large tomato fruit that ripens in a timely manner, these suckers should be removed by pinching them off near the branch between your thumb and forefinger.  In climates that have a longer growing season, some of these suckers may be allowed to grow into main shoots. 

Tomato fruit types include:

  • Cherry tomatoes: small in size (1-3cm in diameter) but profuse in numbers.  Tend to mature earlier than some of the larger types however the endless harvest of small fruit later in the season can frustrate even the most ardent gardener.
    • Recommended cultivars include: Sweet 100 – sweet and tasty, approximately 2.5cm diameter, prolific producer, must be staked; Sweet Million – good flavor, more disease resistant than Sweet 100, 2.5 cm diameter, better tolerance to cracking than Sweet 100;  Vilma – early maturing, dwarf-sized plant with 2cm round fruit, recommended for pots or winter production indoors;  Tumbler – high yielding, good flavor, recommended for hanging baskets or pots; Yellow Pear – small (0.75cm), pear shaped, yellow fruit with mild flavor and attractive color.
  • Beefsteak types vary in size and maturity.  Fruit is round to flattened globe shape and 3-10cm+ in diameter.  Earlier beefsteak types tend to be smaller in size.
    • Recommended cultivars include: Duchess – early, round and small (5cm), productive, average flavor; Cabot – early, good yields, small, sweet and mild; Scotia – early, nice interior color, good yields of small fruit, juicy; Bella rosa – nice flavor, juicy, attractive medium sized fruit, average yields; Early Girl – good flavor, juicy, good yields of medium sized fruit; Tasti-lee – very good flavor, firm fruit, medium size with average yields; Fantastic – good flavor, large size with average yields, matures mid-late season; Celebrity – good flavor (more acidic than others), attractive with average yields, fruit shoulders tend to crack; Champion – medium to large size, juicy, tasty good yields and vigorous plants;  Defiant – medium size and mid-season maturity, average flavor, resistant to late blight;  Lemon Boy – medium-sized round yellow fruit, early to mid-season maturity, low acidity (recommended for people unable to tolerate the acid in tomatoes)
  • Paste or Roma tomatoes are plum-shaped and more “meaty” in texture than the beefsteak types.  The meatiness and thick flesh make paste tomatoes most suitable for cooking, freezing, canning and drying.
    • Recommended cultivars include: Monix – small plant with good yields of fast-maturing fruit; Roma – standard type with good yields and average flavour; Plum Regal – superior flavour, recommended for sauces, has good disease resistance including late blight resistance.

Harvesting

  • For the best tomato flavour, tomatoes should be harvested when they are vine ripened.
  • Tomatoes will ripen off the vine if picked at the ‘mature green’ or later stage.  Mature green refers to tomatoes that remain green in colour but are physiologically mature and will ripen to red (or yellow) off the vine with good flavor and quality.  Because it is difficult to determine when tomatoes are mature green, these tomatoes are often picked only immediately prior to the final killing fall frost.  At this point, most gardeners will try to salvage as much produce from their garden as possible.  A green mature tomato will ripen indoors under proper storage conditions.  The tomato breaker stage is indicated by a slight pink or red coloration to the fruit, at which time it will fully ripen off the vine.

Storage

  • Mature green tomatoes will store for 2-6 weeks at 15˚C.  Tomatoes at the breaker stage will fully ripen off the vine at temperatures above 15˚C.  Ripe red tomatoes will store at 15 - 22˚C for 5-10 days. 
  • Temperatures much below 10˚C will cause tomato chilling injury, resulting in rot and poor ripening colour and quality.

Disorders and Diseases

-        Tomato problems are more often caused by poor growing conditions that lead to what are called “physiological disorders” than by diseases. 

-        Common tomato disorders include:

  • Catface – characterized by misshapen fruit, especially on the blossom end, with corky scar tissue forming on the fruit surface.  Catface results from improper pollination due to adverse growing conditions (cold weather, too wet).  Some cultivars are more prone to catface than others.
  • Blossom end rot (BER) – appears as light brown patches on the blossom end of the fruit.  These brown patches eventually turn black and become sunken.  Blossom end rot is caused by calcium deficiency.  Usually calcium is not deficient in the soil but unfavorable growing conditions – usually drought followed by heavy irrigation, rapid plant growth and high humidity will result in a lack of calcium being absorbed by the plant from the soil.  To prevent BER, provide adequate fertility with even moisture throughout the growing season.
  • Sunscald – occurs when tomato fruit is exposed to excessive sun by over-pruning or defoliation caused by a disease.  Sunscald is characterized by a yellowish patch forming on the tomato surface on the side facing the sun.  Eventually, this yellowish patch becomes grey and blister-like. 
  • Growth cracks – are most likely to develop on tomatoes that have been exposed to heavy rain after a period of drought.  To prevent growth cracks, provide even moisture throughout the season.
  • Blotchy ripening – can be a physiological disorder or a disease.  Conditions favoring excessive growth or extremely high air temperatures can result in blotchy fruit ripening.  If leaves have a light and dark green mottled appearance, blotchy ripening is more likely cause by tomato mosaic virus (TMV).  Because TMV has a wide range of host plants, it is important to keep gardens weed free.
  • Physiological leaf roll – is a temporary condition caused by irregular watering.  Symptoms include upward and inward rolling leaves that are tough and leathery.  With normal, regular watering, plants should return to normal within a few days.

 

-        Common tomato diseases on the Prairies include:

  • Bacterial spot (Xanthomonas campestris) – is characterized by dark spotting on leaves, stems and fruit.  Spots on the leaves appear greasy, while those on the fruit are rough, black and slightly raised.  To prevent bacterial spot, purchase seed that is hot water treated to kill disease organisms (noted in catalogues as HWT), avoid water splashes between plants, place crops in the garden on a minimum 3 year rotation (do not include other solanaceous plants, i.e. peppers, tomatoes, eggplant, in this rotation), use drip irrigation if possible to reduce water splash on leaves.
  • Early blight (Alternaria solani) – is characterized by small, dark brown to black irregular shaped lesions that will eventually be surrounded by concentric rings on the tomato foliage.  These lesions increase in size but are confined within the leaf veins.  Lesions kill plant tissues and the leaf will eventually die and fall off the plant.  As more leaves shrivel or fall off, fruit yields decrease and the remaining fruit suffers from sunscald damage or aborts.  Early blight is common in the environment: some cultivars are more susceptible than others. 
  • Late blight – is a fungal disease caused by Phytophthora infestans.  Late blight is a devastating disease that can kill an entire tomato, pepper, eggplant or potato patch in a couple of days.  The first sign of late blight is a water-soaked area usually at the margin of the leaves.  The lesions run across the veins, as opposed to early blight where the lesions are typically confined by the leaf veins.  In dry weather, late blight lesions stop growing and turn dark brown and brittle.  In wet weather, the lesions grow quickly, with the older, darker areas of the lesion surrounded by a pale yellowish halo.  A white fungal growth can sometimes be detected on the underside of infected leaves, especially on dewy mornings.  Infected stems and petioles will turn dark brown or black.  If late blight infection is suspected in a tomato or potato plant, remove the infected plant immediately and bury the plant in the soil or burn it.  Do not place the infected plant in your compost.  Ripe, good quality tomato fruit harvested from plants infected with late blight can be eaten but will not store.  To prevent late blight, plant only healthy transplants, avoid watering in the evening (late blight spores require high humidity or water to germinate), protect foliage prior to infection with copper-based fungal sprays such as Bordeaux mix and plant late blight resistant cultivars such as ‘Defiant’, ‘Mountain Magic’, ‘Plum Regal’ and ‘Legend’.
  • The best method of controlling diseases in tomatoes is to prevent them from occurring in the first place.  Plant disease-free and disease resistant cultivars.  Place tomatoes on a minimum three year rotation in the garden (do not include other solanaceous crops (i.e. peppers, potatoes, eggplant) in this rotation.  Control weeds in the garden.  Avoid watering in the evening or at night and if possible, use drip irrigation.  Provided even moisture and adequate nutrients to growing plants and developing fruit.

Pests

-        Cutworms – are fleshy worms 1-2cm in length and can be brown or grey to green in colour.  When disturbed, the cutworm curls up into a tight ‘C’ position.  As the name suggests, cutworms ‘cut’ or eat stems and foliage of many types of flowers, perennials and vegetables.  Cutworms often prefer the fresh, succulent tissue of newly emerged plants and transplants as well as fruit and foliage later in the season.  Prevent cutworm damage to transplants by placing tin cans or milk cartons with the tops and bottom removed around newly planted tomatoes.  Insert the containers several centimeters into the soil to provide a significant barrier.  Stake and cage tomato plants to ensure developing fruit and foliage are kept off the soil away from cutworms. 

-        Whitefly – can be found on field-grown tomatoes if greenhouse grown transplants are infected.  Whiteflies are tiny (2-6mm), soft-bodied, white flying insects that suck sap from the tomato plant and deposit honeydew onto the developing fruit and foliage.  Whiteflies usually will not kill a tomato plant however; they can be annoying and reduce yields.  Whitefly excrement or honeydew can result in stickiness on plant foliage and fruit.

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