Lenore Linton, Master Gardener
Part 2 of 2
Each fall before the garden is dug, an inch of our home compost is spread over the garden. The garden is dug by hand and left in lumps that are broken down by winter frosts. By spring the clods of soil have broken down and the garden needs only a light raking to smooth the surface before planting, and our heavy Red River soil is made soft and friable. When choosing where in the garden to place 13 tomato plants I am mindful of their need for a minimum of 6 hours of sunlight each day, as well as the need to avoid planting where tomatoes were planted last season. As sunlight is most important I often plant where tomatoes were grown the year before.
Before planting my tomato transplants my husband hammers in strong metal stakes (old iron water pipes that have been painted). These stakes are placed 2½ feet apart in rows about 3 feet apart and are hammered about 1 foot into the ground. Each stake is 4 to 5 feet tall, but some varieties such as the indeterminate (vining) Sungold need stakes that are 6 feet or more. Determinate (bush) varieties need only 3½ foot stakes that help support the tomato cages. My spacing is a little closer than the recommended 3 feet apart and 4 feet between rows.
The soil beside each stake is amended further with 2 or 3 shovelsful of compost or Sea Soil as well as 1½ cups of fertilizer with calcium for tomatoes 4-6-8. These amendments are thoroughly mixed into the soil ready for the transplants.
If the soil has warmed and the transplants have developed a robust root system it is time to plant them in the garden. Depending on the weather this is usually between May 15 and 25. By this time my transplants are accustomed to the outdoor environment as they have been growing in the open cold frame for 2 or 3 weeks with the lid closed only on frosty nights. I pick a calm cloudy day or evening for planting. This allows transplants to settle in without the stress of wind and heat.
I dig a large hole beside each stake allowing each transplant to be planted deeply covering the stem to the first set of leaves. This will encourage more roots to grow from the stem. If a transplant is on the tall and spindly side I plant it on its side; this allows more stem to be covered with warmer soil near the surface. At this time I also protect the plants from cutworms by wrapping the stem loosely with aluminum foil making sure about ½ inch of the foil is below the soil and another inch or more is above. I attach a tag with the name of each variety at the top of the stake. Each plant is watered in well with a solution of liquid fish fertilizer 2-5-1. Larger taller plants are tied loosely to the stake at this time while smaller plants are tied on as they grow.
Tomatoes require a lot of water to grow and develop fruit. I water tomatoes early in the day, thoroughly soaking the soil and I avoid wetting the leaves. Frequent light watering results in a weak root system. About a week after planting I give the plants a thorough watering before mulching with straw. A mulch of straw will reduce water evaporation from the soil and prevent soil-borne pathogens from splashing up on the plants when watering or during rain.
Another important reason for ensuring that tomato plants are never allowed to dry out is to avoid a condition called blossom end rot, identified by a black or brown rotten spot on the blossom end of the fruit. This is caused by a lack of calcium in the plant tissue as calcium is absorbed by the roots along with water. If water is inadequate so is calcium, even if there is ample calcium in the soil.
If we do not receive significant rain my tomato plants receive a thorough watering at least once a week and more often if the weather is hot and windy. Once they are blooming and fruit is starting to set I fertilize every other week alternating between fertilizer spikes for vegetables 2-7-4 and tomato fertilizer 4-6 8.
How and when to prune tomatoes is a topic where there is much discussion and disagreement among tomato growers and one for which I have received criticism. All agree that determinate tomatoes do not need pruning. However, there are conflicting opinions on when and how to prune indeterminate tomatoes. Most commercial growers recommend allowing only one stem to grow while pinching out shoots that grow in the joint between the stem and a leaf stalk. The main stem is tied to the stake every 10 or 12 inches as it grows. I usually allow the first two side shoots to grow, training three stems up the stake to flower and bear fruit. This increases the amount of fruit and leaves per plant. More than three stems can lead to an overwhelming pruning task.
Anxious for those first ripe tomatoes, some gardeners remove foliage to expose the fruit to sunlight. My experience and observations caused me to question this advice as the first tomato to ripen is usually the first fruit to form near the bottom of the plant shaded by leaves. This caused me do some research. I found the following information in several sources, “Tomatoes do not require light to ripen and in fact, fruit exposed to direct sunlight will heat to levels that inhibit pigment synthesis. Direct sun can also lead to sun scald of fruit. Do not remove leaves in an attempt to ripen fruit”(1). The only foliage that needs to be removed is yellowing or brown leaves at the base of the plant.
Last summer I noticed that some of my tomatoes were ripening slowly and that their tops around the stem were remaining green or turning yellow and hard. These fruits were all on the south side of the plants in bright sun, not protected by leaves. One plant, a Roma type Romana’s Ukrainian, which lacks lush foliage had a heavy set of fruit. This sent me back to Google. The several sources I consulted all gave me the same answers: excessive heat. When ripening fruit is exposed to direct sunlight for prolonged periods lycopene, the plant pigment that gives tomatoes their red colour, is compromised. When the temperatures in the fruit rise above 24C (75F) lycopene production is inhibited.
What caused the yellow shoulders on my tomatoes? Carotene, another pigment in tomatoes responsible for the yellow and orange colours, is not as affected by heat as lycopene and it shines through where the hot rays of the sun have heated the top of the tomato, causing yellow shoulders. Tomatoes with yellow or green shoulders can still be eaten, just remove the affected shoulders.
Excessive heat presents another problem. It prevents chlorophyll from breaking down. Chlorophyll’s persistence and the lack of lycopene can lead to tomatoes with green shoulders.
All sources recommended preventing green and yellow shoulders by maintaining a good leaf cover, planting more densely and by providing shade in the afternoons when fruit is ripening. Craig LeHoullier in his book Epic Tomatoes warns against excessive pruning of foliage. “Tomato flavors develop because of photosynthesis going on in the leaves. One of the reasons that indeterminate tomato varieties are generally more intensely flavored than determinate varieties is the vastly increased leaf area which allows far more chemistry to go on in the plants and results in increased flavor”(2).
In my research I learned that excessive heat and humidity when tomatoes are blooming also results in a reduced fruit set.
Scientists tells us that one of the results of climate change will be hotter summers and more torrential rain storms on the prairies. If this comes to pass prairie gardeners will have to cope with heat and humidity problems faced by gardeners further south.
1: Cornell University Vegetable Program https://cvp.cce.cornell.edu/submission.php?id=91
2: LeHoullier, Craig. Epic Tomatoes. North Adams, MA: Storey Publishing, 2015. This book is available at local book stores as well as the Winnipeg Public Library and is an excellent resource with pictures to identify tomato problems of fruit or foliage.