Growing Tomatoes: Tips from a Horticulturist

Nothing beats home-grown tomatoes! Tangy-sweet fruits bursting with summer flavor and available without a trip to the grocery store. This is why at my house we divide the year into “tomato season” and “not tomato season,” and tomato season opens up with much fanfare. Below are my tried and true growing tips for great tomatoes.

SOIL PREP FOR GROWING TOMATOES

We begin by ripping out the remaining cool season veggies: bolted lettuce, yellowing pea vines, and tired kale. These crop residues get added to the compost pile to break down and become soil-enriching organic matter for side-dressing our summer crops in a few months. Next, we amend the soil in our raised beds with the previous season’s compost. This replenishes soil nutrients and helps improve soil structure and water-retention properties (I can’t impress enough the importance of maintaining optimum soil health in growing successful plants – don’t forget to feed the soil!). Finally, we make sure the drip irrigation is in good working order (squirrels and other rodents are the main culprits for chewing through dripline). Now we’re ready to plant, right? Not necessarily.

WHEN TO GROW TOMATOES

Tomatoes are a warm-season crop and can be damaged or stunted if planted too early. That’s why instead of planting based on a specific calendar date, I like to make sure to plant well after the last frost, when nighttime temperatures are reliably in the mid-50s, before setting out tomato seedlings. As in most aspects of gardening (and life) patience is a virtue; but if you can’t resist the urge to get started you may have better success with early-season varieties such as: ‘Stupice,’ ‘Siletz,’ ‘Glacier,’ ‘Siberian,’ or the ever popular ‘Early Girl.’

If tomato season hasn’t yet arrived in your neck of the woods, don’t fret! There’s still time to start tomato seeds of your favorite varieties (or plan which varieties to pick up from your local garden center as seedlings or “starts” later) and plan out the perfect tomato patch.

WHAT TOMATO VARIETIES SHOULD YOU GROW IN YOUR VEGETABLE GARDEN?

My first recommendation is to plant the types of tomatoes your family likes to eat. Happy plants can be extremely productive so be sure to choose varieties that suit your needs. There are thousands of varieties among cherry tomatoes, snacking, slicer, paste, and beefsteak types in colors ranging from nearly white, bright yellow, striped, green, orange, red, brown, and almost black. You can opt for open-pollinated heirloom varieties (save some seeds to plant the following year), or modern hybrids.

Determinate vs Indeterminate Tomato Plants

Next, you’ll consider whether to grow determinate or indeterminate varieties. This refers to the type of growth and overall habit of the plant. Determinate plants stop growing once the branches set flowers, giving them a shorter, bushier appearance. Indeterminate varieties, on the other hand, keep on growing and often take on a more vine-like habit. This type will have fruit mature progressively over the entire season, weather permitting. I usually grow both types — most heirlooms are indeterminate — and keep their habit in mind when planning out where to locate each plant in the garden.

DAYS UNTIL TOMATO HARVEST

Seed packets and nursery labels are usually clearly printed with the number of days until harvest. This is about how long it will take for plants to bear mature fruit once they are set out in the garden, and will vary between varieties (although determinate types tend to set fruit earlier).

Planning for harvest times ensures you’re not overwhelmed if several varieties ripen all at once. This is especially true of determinate plants, which set their fruit over a short period of time (a boon if you want to process a large volume at once for canning). One strategy is to set out plants with similar days to harvest over subsequent weeks in order to stagger the harvest.

WHERE DO TOMATO PLANTS GROW BEST?

Full sun is best for all types but especially important for large-fruited varieties, like beefsteaks, which need maximum sunlight to produce large, tasty fruit. Select a site that will get at least 6 hours of direct sun. If you experience extreme summer heat, your plants may benefit from a bit of afternoon shade.

With proper planning, tomatoes can be grown successfully in-ground (including raised beds) or in containers. Most tomatoes need at least 12 inches of soil depth, but the taproot of larger types may extend 18 inches or more into the soil.

The smaller stature of determinate varieties makes them better suited to containers than their vining counterparts. Check the seed packet or nursery label for key words like “dwarf,” “patio,” or “container variety” for good candidates. Choose a pot at least eighteen inches in diameter and use a high quality potting soil (organic brands are available if you plan on growing organically). Make sure to monitor soil moisture closely, since containerized plants will dry out faster than those planted in the ground. Stake or cage just as you would for planting in the ground.

Plant Tomatoes at Proper Depth and Spacing

Unlike most other plants, tomatoes like to be planted deep. Dig a hole about 10-12” deep and add a small handful of compost or organic fertilizer in the bottom. Remove any leaves that will be below the soil level and gently cover about two-thirds of the plant. The section of stem underground will form adventitious roots which results in a larger, deeper root system to support more vigorous growth.

To minimize plants shading each other, allow at least two feet between each plant. This will also increase air circulation which will help prevent fungal diseases, as well as make spotting pests like tomato hornworm easier. If planting multiple rows of tomatoes, orienting them North to South and spacing rows about four feet apart will maximize light exposure and airflow, and allow space to walk between rows for pruning and harvesting.

To Mulch or Not to Mulch?

I don’t find mulch necessary in raised beds since plants are grown closer together and shade out any weeds that might try to pop up. Exposed patches of soil can be planted with warm-season annuals like sweet alyssum and zinnias. In addition to adding cheerful pops of color among the jungle of green, these flowers attract pollinators and beneficial insects such as predatory wasps and ladybugs, which deter caterpillars and phloem-feeding insects like aphids and whitefly. Marigolds are also thought to reduce the effect of root-knot nematodes on tomato plants.

There are situations that lend themselves more to using mulch. If you are growing multiple rows of tomato plants with space between, mulch will help suppress weeds and retain soil moisture. Organic mulches improve soil structure as they break down and enter the soil profile. Suitable materials include: weed-free straw, untreated (herbicide-free) grass clippings, shredded leaves, and bark-based products. Apply 2-3” to garner the full benefits, making sure to keep it a few inches away from stems to discourage fungal issues.

You can also experiment with layered newspaper or cardboard, but might find (as I have in my Southern California garden) that these tend to harbor pests such as earwigs, pillbugs, and slugs — making the cost of these materials outweigh the benefits.

Plastic sheeting is yet another option, but isn’t my favorite due to the fact that it is used for only one season and then thrown away. If using plastic, it is put in place before plants are set out in the garden (cut a slit or “x” in the sheet to plant each tomato). One benefit of plastic sheeting is that it traps heat and allows you to plant in the ground sooner than with exposed soil and can help protect young plants from late frosts, as well.

HOW TO SUPPORT GROWING TOMATOES

Due to their vining nature, indeterminate varieties need vertical support to keep plants from sprawling across the garden. This also helps keep fruit off the ground, where it is more susceptible to ground-dwelling pests. Use sturdy posts made of wood (at least 1” diameter) or metal that are at least 6-8’ long, since you’ll sink the first foot or two into the ground to ensure they’re stable enough to support the mature vines and strong winds . Place plants about 4” from the base (you can bury plants at an angle when planting) and periodically tie them up using twine or stretch ties as they grow.

Determinate varieties don’t require as much vertical space and can be staked as above (shorter stakes may be used) or supported by tomato cages or trellises. If using commercially available cages, be sure to select the largest size available. Smaller cages standing around three feet tall are more suitable for peppers — I wouldn’t suggest anything shorter than four feet tall for tomatoes.

HOW TO GROW PRODUCTIVE TOMATOES

All tomatoes produce side branches known as suckers. Removing them isn’t necessary with determinate tomatoes since they aren’t vigorous enough to overtake the plant and will actually contribute additional fruit. However, if suckers are left unchecked on indeterminate plants, the vines will quickly become a tangled mess and yields may be reduced due to branches shading each other and numerous fruit competing for the same nutrients. Thankfully, spotting suckers is easy once you know what you’re looking for: check where leaves meet the main stem and pinch out any small shoots forming in the joint (axil). Doing this about once a week will help keep indeterminate vines tidy and productive—so you can grow lots of tomatoes—not just tomato leaves!

Best Fertilizer for Growing Tomato Plants

Tomatoes are heavy feeders, with an especial appetite for phosphorus and potassium (the second and third numbers in the trio printed on fertilizer labels). If you opt for a commercial fertilizer there are both organic and synthetic products formulated especially for tomatoes. With all fertilizers, be sure to follow the package directions regarding application rate, frequency, and timing.

I prefer to amend garden soil with homemade compost at planting time (sometimes I sprinkle in some bonemeal to provide an additional phosphorus boost), and then side-dress with compost again once or twice during the growing season. I find this provides enough nutrients for my plants’ needs.

How Much Water do Tomatoes Need to Grow?

Deep, consistent watering is crucial for a healthy fruit set. Fluctuations in soil moisture can lead to a calcium-deficiency disorder called blossom-end rot, as well as cracked skin on maturing fruits.

Foliage should be kept dry, so watering directly at the soil’s surface is preferable. This can be done by slowly drenching the soil with a traditional hose set on the ground (set a timer to ensure you remember to turn it off), or by utilizing a soaker hose or drip system. The latter two options can be automated via an electronic irrigation controller. You could also take this a step further by installing a smart irrigation controller, which references local weather data and adjusts irrigation cycles and inches of water as needed.

Whatever your method, make sure to apply enough water to dampen soil at least 8-10 inches below the surface. This will encourage deeper roots, and create a reservoir the plants can draw from until the next watering.

ENJOY THE JOURNEY, AND YOUR RIPE TOMATOES!

Whether you grow just one patio tomato on your sunny urban balcony, or plant multiple rows to share summer’s bounty with family and friends, I hope you enjoy your tomato-growing journey. If for some reason your tomato crop falls short this season, don’t worry — there’s always next year! Have fun experimenting with different varieties or trying out new fertilizer regimens to find what works for you—and produces the best tomatoes in your yard. Happy planting!