assortment of all types of heirloom tomatoes in many shapes and shades of red, orange, yellow, green, and purple

Tomatoes 101

Updated on Jan 02, 2025
By John Lenz

Tomatoes are a beloved – and often vexing – garden crop, and our horticulture experts frequently field questions about the best way to germinate, plant, and tend them. We put together this brief guide to tomato basics, which we’re calling “Tomatoes 101.” 

Queesn of the Night tomatoes have dark red interiors under a blue-black skinQueen of the Night tomatoes are delicious and high in antioxidants!

What is Germination? 

Seed germination is the process of a plant emerging from the dormant seed. Its success depends on many factors, such as light, temperature, moisture, and nutrients in the soil. Tomatoes germinate best  at soil temperatures between 70 F and 80 F. You can check the temperature by sticking an ordinary meat thermometer into the soil. If you are starting the seeds indoors, you may need a heat mat in addition to the grow lights to maintain the soil temperature.

What are "Seed Leaves" and "True Leaves"?

When a seed germinates, the first leaves to emerge are seed leaves or cotyledons for dicot type (two seed leaves) plants. (Monocots are the grasses in general.) These seed leaves are not the true leaves of the plant; they are just the starters. They photosynthesize and provide energy to the young plant. After the plant gets established and has a root system, the true leaves will begin to emerge, and the plant starts growing. 

tiny tomato seedling in peat pot showing true leaves and seed leaves

Tiny "true leaves" can be seen in the center; the larger two at top and bottom are the "seed leaves."

What is "Hardening Off"?  

Hardening off is a process where you prepare your indoor grown seedlings to be planted outside. Indoor-grown seedlings are accustomed to constant temperatures and low light levels. Placing them immediately outside can result in transplant shock from the intensity of the sunlight and the temperature swings. To counter this, bring your plants onto a covered porch or a protected area and let them get a couple of hours of sun each day. Gradually increase the amount of sun over the course of a couple of weeks. Then, when you plant, the seedlings will have hardened off. The hardening-off process is an important way of acclimating your seedlings to outdoor conditions! 

tomato seedlings in a seed tray in the sunlightAllow your seedlings to experience the outdoors from the safety of their trays before transplanting

Should I Side Dress My Tomato Plants? 

Side dressing is the process of applying a mid-season fertilizer. For longer season crops, you can fertilize before planting to get the plant started, but it's dangerous to try to apply a whole season's worth in the spring. Rather, apply fertilizer to the side of your rows in mid-season to provide a boost to your crops. This can encourage a higher yield in the late season.  

What is the Best Tomato Fertilizer? 

There is no one best tomato fertilizer. We recommend using an organic fertilizer pre-plant and side dressing throughout the season to maintain vigorous growth. Small frequent applications result in an even growth rate, while a large application can result in flush of unwanted growth.  

Tomato vine with unripe green tomatoes and yellow blossomsA healthy tomato vine in the garden

What’s the Best Way to Water My Tomatoes? 

The best way to water tomatoes is with drip and a timer. This way provides a nice consistent amount of water to the plant and eliminates the wet/dry cycle and provides better results. Hand watering is OK, just try not to wet the foliage. Wet foliage can lead to disease. Try not to splash water and soil upon the leaves. With well-draining soil you should be able to water every other day except in the middle of the summer when it may be daily. Plants grown in containers will require more frequent watering due to the restricted root space. 

What’s the Best Way to Prune My Tomatoes? 

Pruning tomatoes is an exercise in imagination. While tomatoes can grow as a rambling vine, they don't climb. We trellis them to keep the fruit off the ground. It is not absolutely necessary to prune tomatoes, but we do, to keep the plant under control.  

Pruning a tomato is easy. Leaves and flowers grow along one main stem. At the junction of the leaf and the stem a side shoot (or sucker) can form, growing laterally from the stem. This sucker will put out its own leaves and flowers and eventually have fruit develop. Suckers will develop all along the stem, and if you don't remove some of them, you end up with an impenetrable mass. Use your imagination and choose which suckers you wish to keep. Train one to the left and one to the right on your trellis. As more suckers grow, choose another pair and train them. Letting all the suckers grow will result in a stressed-out plant and smaller fruit. Keeping the main stem and about four suckers will provide lots of leaf surface and the best fruit. 

What’s the Difference Between a Determinate and Indeterminate Tomato Variety? 

Determinate tomatoes are a type of tomato that grows, flowers, sets fruit, and then stops growing and fruiting. The vines tend to be shorter, easier to maintain and control, and a little more bushy. Dwarf tomato plants generally fall into this category. Martino's Roma, Micro Tom, Orange Hat, Principe Borghese, and Purple Reign are the only determinate varieties we currently offer.

Indeterminate tomatoes grow, flower, set fruit and continue growing and fruiting for the rest of the season--usually until first frost. Indeterminate tomatoes are by far the more common type, and most of the varieties we offer are indeterminate.

Semi-determinate tomatoes aren't so easily categorized.  In general, while they tend to have shorter, bushier vines, they often need some kind of support (trellising or caging) but do not tend to grow out of control. Some semi-determinate varieties will produce fruit in spurts (rather than constantly) throughout the season. Peron, Phil's Two, Raspberry Lyanna, and Thorburn's Terra Cotta are the only semi-determinate tomatoes we currently offer.

Can I Grow Tomatoes in a Container? 

Tomatoes can be successfully grown in containers. A 5-gallon bucket is probably the smallest suitable container size, and even that will restrict the root zone. Container growing requires paying close attention to the soil moisture and applying regular small doses of fertilizer to maintain growth. 

2 terra cotta pots with tiny yellow tomatoes on small, bushy plantsTiny Gourmandise Yellow tomato plants thrive in pots!

How Do I Know if My Tomatoes Are Ripe? 

The squeeze test is the best way to check a tomato’s ripeness. Gently squeeze the fruit, and if the flesh gives a little, it’s ready. If it feels soft, it's overripe, and if it doesn't give at all, it's not yet ripe. Judging ripeness by the change in skin color also works, but it’s not as reliable a method. 

hand holding a ripe tomatoGently squeeze your tomato to determine ripeness.

What’s the Best Way to Support Tomato Vines?  

Trellising is the best method for raising tomatoes. This method keeps the fruit off the ground, increases sun exposure, increases potential airflow, and allows for easier pruning. Staking and caging will also work, but if your tomatoes are growing well, they will soon overwhelm a caging or staking system. At Baker Creek, we use wire cattle panels in the greenhouses and tomato fields. 

green tomatoes and fines on a wire mesh cattle panel trellisWire mesh cattle panels work well to trellis your tomato vines!

What Should I Know About Tomato Pollination? 

Tomatoes are self pollinating. This means they have complete flowers with both the female and male parts. As such they don't need pollinators to transfer pollen from one flower to another in order to set fruit. 

How Do I Save Tomato Seeds? 

When saving tomato seeds from one season to the next, it is necessary to ferment them. This process allows microorganisms to break down the gelatinous material that protects the seeds.  

Tomato seeds are ready to harvest when the fruit is ready to eat. For easy seed extraction, cut the tomatoes in half. Squeeze or scoop the seeds and pulp into a clean container (a Mason jar works well). Cover the seeds and pulp with an equal amount of clean water. Stir vigorously. Covering the jar is optional but note that it might be necessary to burp the jars as gases will build up from the fermentation process. Stir the seeds daily, and after three days pour off the water and floating goop and collect the seeds from the bottom of the vessel. Dry the seeds for several days, then place the seeds in a clearly labeled bag. 

tomato seeds being rinsed off on a mesh screenTomato seeds being rinsed on a mesh screen to save for next year's garden!

Key Takeaways: 

  • When transplanting tomato seedlings, get them used to outdoor conditions by exposing them to short periods of outdoor temperatures and sunlight each day for a couple of weeks. This process is called “hardening off.”
  • Be careful not to overfertilize the soil before transplanting tomato seedlings. A better strategy is to side dress your plants mid-season by applying fertilizer alongside the rows or plants.
  • Using drip irrigation and a timer is the best way to water tomatoes. If hand watering, be careful not to splash water and soil onto the leaves as that can lead to disease. Water the soil, not the plants!
  • Tomatoes can be grown in containers but choose one large enough for the plant’s root system to expand. Tomatoes shouldn’t be grown in anything smaller than a 5-gallon bucket.
  • For the best results, trellis your tomato plants rather than using stakes or cages. This gives the plants more sunlight and airflow, allows for easier pruning, and keeps the fruit off the ground.

Multicolored small tomatoes, with two cut in half to show multicolored interiors
Brad's Atomic Grape tomatoes are prolific, beautiful, and delicious

About the Author:

Bearded man in brown cap carries an armload of large cabbagesHorticulturist John Lenz in the garden

Visitors to Baker Creek’s Mansfield, MO, seed store may know John Lenz as an affable and loquacious storekeeper, but he is also a horticulture expert who oversaw our greenhouse program during a time of rapid expansion. He has a degree in horticulture from New Mexico State University and an MBA from St. Leo University in Florida.  Stop in and say hello if you are visiting our Mansfield, MO, location! 

You can always email your gardening questions to seeds@rareseeds.com. Put "hort question" in the subject line, and John or someone else on the horticulture team will get back to you.