Almost everyone wants tomatoes! The range of colors, shapes and flavors is enormous. The taste of a fresh-from-the-vine, unsprayed tomato is infinitely better than that of a tired, much-traveled industrial tomato. Although this crop practically sells itself, it might not be easy money: tomato production can be labor-intensive — 350 hours per acre — and then there is a range of pests and diseases to avoid.
Tomatoes have a range of uses: there are slicing and cherry varieties, paste (processing) tomatoes for sauces, and even special varieties for drying. Varieties can be divided into two growth types.
Determinates are varieties which can only reach a certain size. The number of stems, leaves and flowers is part of the genetic makeup of that variety. The number of leaf nodes between one truss (cluster) and the next decreases by one each time a truss is produced. A point is reached when no more leaves or flowers form. Then the fruit ripens and the plant starts to die back. Harvest can be 3 months from start to finish. Because they tend to be shorter than indeterminates, and faster to mature, they are often chosen for earlier crops. Some determinates, such as Roma, are in fact quite tall, and produce for quite a long season.
Indeterminate varieties can continue to grow taller and produce more trusses of fruit as long as the weather is warm enough, and as long as they don’t get struck down by a plague. The number of leaf nodes between one truss and the next remains the same all the way up the vine. If you don’t have space to plant a succession of tomatoes and want to plant once only and get a long harvest season, choose indeterminates and cage them. This only works if your area is not prone to many diseases.
Factors to consider when selecting varieties include the preferences of your market, suitability for your climate, resistance to or tolerance of, prevailing diseases and suitability for your preferred growing system. Andrew Mefferd wrote about tomato varieties in last month’s Growing For Market. We choose fast-maturing determinates such as Glacier and quick-maturing indeterminates like Stupice for one row in the hoophouse, and our favorite workhorses along with unusual varieties like Green Zebra and Cherokee Purple for the second row. Our maincrop outdoor varieties include lots of Tropic, a tasty disease-resistant round red type, and a mix of a few cherries such as Sun Gold and Black Cherry, oddities like the lovely Garden Peach, orange Jubilee, and the exuberant Striped German. We also grow 250-300 paste tomatoes, Roma, a selection I have been making for the past several years. For our late crop we choose disease-resistant varieties that don’t take too many days to mature.
Tomatoes do best on well-drained, slightly acid soils (pH 6.0-6.8). They need moderate amounts of nitrogen (N) – too much can produce excess foliage and over-soft fruit. 75-100# N/acre is needed. This can be provided by one shovelful of compost per plant, or 5 tons compost per acre. Fairly high levels of calcium (Ca), phosphorus (P), and potassium (K) are needed. Insufficient K reduces the quality and quantity of fruit. Boron (B), iron (Fe), zinc (Zn) and molybdenum (Mb) are also important.
Biologically active soils (“soils in good heart”), if given regular inputs of compost and cover crops can provide most or all of a tomato crop’s nutrient needs, and unless one of the micronutrients is insufficient, there is no need to add concentrated organic fertilizers.
Temperature and water
Tomatoes like temperatures between 62° and 90°F and nights at 55-70°F. Frost will kill them, low temperatures will reduce fruit set, and high temperatures will reduce fruit set, as well as quality.
Tomatoes use a lot of water, although they can survive dry spells because of their large root systems. If soil moisture levels vary widely, fruits can split or suffer from blossom end rot. If too much water is given, flavor deteriorates. Drip irrigation is a good way to ensure regular watering without risking fungal diseases on the leaves. My first venture into drip irrigation was for our long rows of paste tomatoes as a step towards reducing losses from Septoria Leaf Spot. I admit to being a reluctant adopter, but after that first year I was convinced. The costs are quickly recovered by the reduced cull rate as compared to sprinkler systems.
Mulch, either plastic or organic, will help conserve soil moisture as well as reduce weeds. Organic mulches should be applied after the soil has warmed to 70-75°F in order not to slow down production by keeping the soil cool. Plastic mulches require the use of drip tape, as they exclude rainfall.
Tomatoes provide high yields from a small area, and are labor-intensive, so don’t plant too many. Labor estimates are in the order of 350 hours for each staked acre. Yields average 180-250 lbs/100’ of row. With good conditions, organic growers can get yields as high as 750 lbs/100’, or 15 lbs per plant.
Per capita consumption of fresh tomatoes is 20 lbs per year. We grow 250 paste tomatoes and 90 maincrop slicers for 100 people. We can about 500 gallons of sauce.
Cherry tomatoes are fun, and a few plants go a long way. They take a long time to harvest, and some, though delicious, split easily. Sungold is especially notorious for splitting.
How early you start your first tomatoes will depend not only on your climate, but also what facilities you have for keeping seedlings and young plants warm enough, and whether you will be planting them under cover or outdoors. Tomatoes struggle with cold winds. Tomatoes are usually grown as transplants, to take advantage of warmer protected conditions for seedlings, and also because many growers like to grow many different varieties, rather than long rows of the same kind. If you do want to direct sow, the usual method for small plantings is to “station sow” up to 5 seeds at each point where you want a plant, and thin to one plant when the seedlings are a few weeks old. Direct-sown plants can catch up with transplants started a month earlier. Another lower-labor method is to sow in the soil in a cold frame and do bare-root transplanting. Yield is just as high.
Sow seeds about 0.5” deep, 2-3 seeds per cell, or in open flats, aiming for 5 seeds per inch. Plan on six weeks to transplanting (8 weeks in late winter), and work back to figure out your seeding date. For early sowings, use a seedling heat mat or other heating to keep the plants at 75-85°F. When the seed leaves spread open and true leaves start to appear, either single the seedlings (in cells), pot them up individually in 3” pots or spot them out into bigger flats, about 2-3” apart.
The plants are ready to plant out when they are about 6-8” tall, sturdy and dark green. If the plants need to be held in the greenhouse or cold frame longer than expected, you could pot them up into 4.5” pots, or space the small pots out so that each plant gets plenty of light and doesn’t grow leggy. If you do need to delay planting, consider a foliar feed if your potting compost could be running out of nutrients. After a transplanting shift, we often pot up leftover plants from 3” pots into 4.5” pots and keep them for a couple of weeks more until we see whether we need to replace any casualties.
While starts are in the greenhouse, they may be troubled by aphids. Be sure to deal with these in a timely way – a foliar spray of insecticidal soap every five days works well. Sometimes two sprayings will do the job, sometimes three are needed.
Tomato plants are usually hardened off for transplanting by reducing the watering and exposing the plants to more direct sunlight and breezier air, rather than by exposing them to lower temperatures.
We start our first tomatoes (to be grown in the hoophouse) on 1/17, for planting out 3/15, a month or more before our last frost date. These plants need a fair amount of cosseting during their eight weeks in the greenhouse. We use a heating mat, and a small clear plastic mini-tunnel inside the greenhouse, which has no additional heating. It may well be sensible to have a small amount of heating in the greenhouse on very cold nights. These plants will provide crops from the end of May till the end of July or longer, if we need them and disease is not too bad.
For early outdoor crops, grown under row cover, we sow in late February, transplant at eight weeks, and harvest eight weeks after that.
Our main crop tomatoes are sown 3/15, transplanted at 6 or 7 weeks old, and harvested from mid July until frost. Yields do go down after two to three months of harvesting, even if frosts don’t bring the plants to an abrupt end.
We sow 5/14 for a late outdoor crop, to produce fruit from mid-August until frost. In our area, people who want more successions coming in pull diseased plants and sow 2/25, 3/15, 4/3, 4/17 and 5/1.
In the past we have also sown for a late hoophouse crop, to take us beyond the first frosts. Sow 6/18 and transplant at a relatively young age (tomatoes grow quickly by that point of the year).
Determinate varieties usually bear lightly the first month of harvest, heavily the second month, then lightly for the third month, so it is not very productive to plant crops so late that they don’t reach their second (main) month of production before frosts.
Transplanting and spacing
We space our plants 2’ apart in the row, whether in the hoophouse or outside. Our rows are 5’ apart in the hoophouse, and 5.5’ outside (because we often roll bales of hay out in between the rows as mulch, and this is the best spacing — tight, but do-able. Small determinate varieties can be planted closer. Widely spaced plants can give higher per-plant yields. Some growers advocate 3’ in-row spacing, if trellising or using cages.
Tomatoes have a great capacity to grow new roots from the stem, and this trait can be used to advantage if you are planting out over-large or leggy plants. Dig a short diagonal trench and lay a plant with the root ball at the deeper end and its top above ground. (The diagonal planting method is better than simply digging a deep vertical hole — except perhaps late in the season in hot climates — because the soil would be too cold lower down.) I recommend orienting the diagonal holes all the same way, so that when you install stakes, you know which side of the plants the root balls are, and don’t damage them. Cover the roots and stem back to normal ground level. In a few days, the plants will be growing upright again, and will be stronger for the extra roots they grow along the buried stem, and you do not have fragile spindly stems out in the air at the mercy of stiff breezes, bouncing puppies, gamboling groundhogs, etc. In addition, if a late frost wipes out the above-ground growth, new shoots will grow from the below-ground stem.
Cultivation and management
Care of tomatoes involves setting out drip tape or other irrigation; staking, trellising or caging; mulching sooner or later; weeding; and likely some training or tucking of wayward branches. Monitoring and managing pests and diseases also needs time.
Tomato plants usually start to flower and grow side branches after they have grown 10-13 leaves, when the plant is manufacturing more sugar than a single stem can use. It is often recommended to pinch out all but one of the suckers (sideshoots) below the first fruit truss (cluster) especially if using the stake-and-weave system. This helps improve airflow around the plants, reducing the chance of fungal diseases at the price of increasing the risk of sunscald. Over-zealous pruning can result in earlier and larger fruit, but lower total yields. Frankly, we never prune ours. Sometimes when they get too tall we chop them off with hedge clippers. But we live in a climate where tomatoes grow like weeds all summer. When I lived in the north of England, we grew our tomatoes up vertical strings in a glass greenhouse. I pinched out all the side shoots, making a regular weekly job of it. The amount of pruning you do will reflect your climate and your goals. In general, more stems means more but smaller fruit, and a longer fruiting season.
Many growers use black plastic mulch, as it warms the soil, stops fungal diseases caused by “splash-back” from the soil, and prevents weeds growing. We use biodegradable plastic for some of ours. (If you are certified Organic, check with your certifier before using biodegradable plastic as it may not qualify.) Later in the season, we top the disintegrating plastic with hay mulch. We also use hay or straw mulch for our main crop, adding it in the middle of June when the soil has warmed.
For our paste tomatoes we use a no-till method, sowing winter rye, Austrian winter peas and hairy vetch in the fall, mowing it at flowering in early May, and immediately transplanting into the stubble. Austrian winter peas are said to reduce the incidence of Septoria leaf spot. Winter rye is allelopathic, releasing compounds that inhibit seed germination for several weeks after the cover crop is killed. Yields are good with this system. No-till cover crops do prevent the soil from warming as fast in spring, so they are not good choices for crops you want to harvest early. But for our processing tomatoes, earliness is not important, so we can benefit from the advantages of no-till: reduced tractor passes on the field, reduced soil inversion, grown-in-place nutrients, including enough nitrogen to see the crop through till frost, and increased soil organic matter for the next year.
Another approach to mulch is to use landscape fabric with holes burned at the appropriate spacing. This can be rolled up at the end of the year and re-used for many years, although good sanitation will be needed to prevent spread of disease. It also has the advantage of being permeable to rainfall. White on black plastic is sometimes used late in the season, and red plastic mulch is reputed to ripen tomatoes faster.
During the first month after transplanting, it is important to control weeds to ensure the crop gets enough light and water. Tomatoes grow vigorously, and later in life small weeds do not directly threaten the tomato yield. It is, of course, still important to hoe, pull or cut weeds to prevent seeding, and to maximize the airflow around the tomato plants. Repairs can be made to broken tomato stems with electrician’s tape or duct tape, using a splint if necessary.
Because tomatoes are not frost tolerant, possibilities for season extension into the colder parts of the year are limited. In spring, row cover can be used, or a bucket can be put over each plant on cold nights. In fall, it is possible to keep tomatoes alive through a frosty night by running overhead sprinklers all night until the sun comes up and temperatures rise above freezing. We often do this once or twice, as we can get an extended warm spell after the first couple of frosts. Obviously it’s not a good system if you have four frosty nights in a row, as your soil will be waterlogged, and the days are likely to be chilly in between.
Hoophouses offer the best way of extending the season. Under conditions of fast growth and high yields, such as in a hoophouse, plants can run out of potassium. In particular this can happen with the Luminance THB diffusion plastic used on Haygrove tunnels. Because it diffuses light more evenly than Tufflite IV and Solarig 172 plastics, the lower leaves get much more light, and plants grow taller, requiring more nutrients. Single-skinned temporary “field houses” are the next best way to extend the season. Hooped structures can also be made to cover several beds, and a layer of hoophouse plastic or row cover will protect plants.
Another approach to extending the season is to harvest the part-ripe fruit the day a frost is expected and to finish the ripening process indoors. Contrary to rural myth, tomatoes do not need light to ripen. In fact they need warmth, 70°F, so putting them on a drafty windowsill is not so good. We stack ours in pulpboard egg trays, which each hold 30 eggs or tomatoes. (Bigger fruits we put in pulpboard apple trays.) The egg trays have handle cutouts on two opposite sides. Empty, the trays nest with the handles aligned. When filled, they stack best if rotated 90° for each layer. Once a week, check through, and remove the ripe ones and the composting ones. The presence of one or two ripe or nearly ripe tomatoes in each tray will help the others ripen (due to the ethylene off-gassed by the ripe one). Garden Peach is an extraordinarily good storage tomato, much better than Longkeepers.
The Heirloom Tomato: from Garden to Table by Amy Goldman. This beautiful book has detailed information on flavor and disease-resistance as well as mouthwatering photos.
ATTRA Organic Tomato Production: https://attra.ncat.org/attra-pub/summaries/summary.php?pub=33 https://attra.ncat.org/attra-pub/summaries/summary.php?pub=33
Pam Dawling is garden manager at Twin Oaks Community in Virginia. The gardens provide nearly all the fresh and preserved produce for the community’s 100 residents. Her book, Sustainable Market Farming: Intensive Vegetable Production on a Few Acres, is scheduled for publication this fall. She can be reached at [email protected].