It’s tomato time for many of us living in the Coeur d’Alene region—a time when hope and optimism run high as we head to the garden, dreaming of picking big, juicy tomatoes, snacking on sweet cherry varieties bursting with flavor, or making jars of salsa!
But first, we need to get them in the ground.
Whether this is your first time planting tomatoes or your hundredth, here’s a little refresher on how to get your tomato plants off to a great start.
Know When to Plant
Tomatoes are warm-season crops that thrive in warm growing conditions, including soil temperatures of at least 50°F. They are highly susceptible to frost, so knowing the last average frost date is essential for success.
For the Coeur d’Alene area, that date was May 15th; however, the last frost date can extend into June for gardens in northern regions or higher elevations (find your frost dates here). The date is an average, so it’s a good idea to have frost protection, like row covers, on hand for chilly evenings or unsettled weather.
Ensure seedlings have been hardened off and acclimated to outdoor growing conditions before planting. Hardening off enables plants to adapt gradually to sunlight and weather conditions.
Seedlings planted directly from an indoor growing environment to outdoors will quickly perish from full sun or harsh weather conditions.
When transplanting, choose a calm, overcast day, or schedule your planting for later in the afternoon when the sun is less intense. Excessive sun, heat, or wind can quickly wither young plants.
Where to Plant
Location, location, location—it matters for ‘maters! Plant tomatoes in the sunniest location possible. They are sun-loving plants and need at least 6 hours to be productive.
They also need well-draining soil, so avoid planting in wet or soggy locations. If your garden soil retains water, amend it with compost to improve drainage and soil structure.
Tomatoes don’t like “wet feet,” meaning their roots sit in water. Poor drainage can lead to diseases and root rot in container-grown tomatoes, so ensure that your growing medium is well-draining and that containers have proper drainage holes.
To keep your plants and soil healthy, avoid planting tomatoes in the same location year after year or in areas where other nightshade plants, such as peppers, potatoes, and eggplant, have recently grown.
Nightshades share common diseases, including blight, wilt, bacterial spot, and anthracnose, which can persist in the soil for many seasons.
How to Plant
Tomatoes must be planted deeply, whether in the ground or a container. Approximately two-thirds of the stem should go below the soil, with one-third remaining above. This applies to any size transplant, including micro-dwarf varieties.
Why so deep? The reason lies in the specialized cells found along the tomato stem, called parenchyma, commonly known as adventitious roots. You may have noticed bumpy nodules around the base of your mature tomato plant; these are the parenchyma cells.
Above ground, the cells assist with photosynthesis, but underground, they grow into roots. More roots provide greater nutrient absorption, resulting in stronger and healthier plants.
If deep planting isn’t possible, tomatoes can be planted by trenching: placed on their side in a 6-inch trench, covering the roots and lower two-thirds of the plant stem with soil. The top of the plant is gently bent upward.
Space tomatoes approximately 18 to 24 inches apart to allow good air circulation between plants. Remember to place cages or supports around your tomatoes at planting time, not after they’ve grown two feet tall!
For container growing, indeterminate tomato varieties should be planted in 10-gallon containers at least 16 inches deep to provide adequate root space. Determinate or dwarf varieties can be grown in 5-gallon containers, also 16 inches deep. Only one plant should be planted per container.
Watering & Plant Maintenance
Tomatoes need one to two inches of water each week, applied slowly and deeply at the base of the plant. Watering early in the day enables plants to absorb more moisture before the day’s heat.
Avoid shallow watering, which leads to shallow roots and unstable plants, as well as overhead watering, which encourages diseases while providing minimal water to the roots.
Additionally, a layer of mulch, such as herbicide-free grass clippings, leaves, or straw, placed around the base of the plant, helps retain moisture and prevent weeds.
Tomatoes are highly susceptible to various soil-borne fungal diseases, like early blight. Fungal spores can easily be transferred from the soil to the plant’s leaves by splashing water or a breeze.
To minimize disease risk, prune the lower leaf stems and pinch back any upper leaves that contact the soil surface.
As the plant grows, continue to prune the lower stems until there is approximately 8 to 10 inches of space between the lowest set of leaves and the soil. This reduces leaf-to-soil contact and allows access to the plant’s base for watering and applying mulch.
Indeterminate tomato varieties should also be pruned for good air circulation through the plant. Bushy and dense plants can become a haven for foliar diseases like powdery mildew. Avoid pruning suckers from determinate varieties as this will reduce the plant’s productivity.
Tomatoes are self-pollinating; however, they are particularly finicky, fair-weather plants that need a temperature range of 70°F to 85°F for pollination and fruit set to occur.
Pollination ceases when temperatures are below or above that range, and the flower blossom dies. Yet another reason not to plant tomatoes too early in the spring!
The key to tomato success is planting at the right time, planting in the right place, and giving your plants the support they need to thrive. With that, you’ll be on your way to harvesting a bounty of juicy, homegrown tomatoes this summer, and maybe even a few jars of homemade salsa!
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