Starting from Seed

Introduction

Once you’ve started tomato plants from seed successfully, you will probably never give a second thought to reading a How To website on the subject. Given the right conditions, tomato seedlings practically grow themselves — it really is that easy. After all, tomatoes and their wild brethren have been growing for millions of years without human intervention.

And yet Seed Starting articles tend to be lengthy and full of detail. Why is this?

As it turns out, each tomato contains hundreds of seeds. Tomato seeds, like all seeds, germinate at their own leisure whenever sunlight, water, and soil conditions are viable.

Creating the perfect conditions to produce healthy tomato seedlings is made more complicated by the wide variety of soil products, seed starting materials, fertilizers, and lighting options available. Sorting through them to find the most reliable methods takes further explanation.

However it’s worth learning how to successfully start your own seeds, so you can grow the exact tomato varieties you want. Counting on your local nursery to have your favorite tomato variety at the time you need it inevitably leads to disappointment, especially for varieties which are not best-sellers.

Step-by-Step Instructions

Let’s start with the basics. This is the step-by-step instructions on growing tomato plants from seed to seedling to transplanting into your garden. We’re going to keep this section as free as possible from unnecessary details. We’ll then extrapolate on those subjects in separate sections below.

Materials You Will Need:

• Sterile Seed Starting Mix (an 8 quart bag is ~$4)
• Seed starting tray or plastic pots
• Large mixing bowl
• Tomato seeds
• Trowel
• Water
• Liquid fertilizer (i.e. Maxicrop liquid seaweed, Alaska fish emulsion, HastaGro 6-12-6, etc. — $6-12)
• 40W 4′ fluorescent light fixture with adjustable chains ($25)
• 40W 4′ Daylight fluorescent bulb ($6)
• 40W 4′ cool white fluorescent bulb ($3)

1. Make sure seed starting tray, pots, mixing bowl, and trowel are clean. If necessary, rinse with 10% bleach solution.

2. Pour dry seed starting mix into large mixing bowl and moisten until just damp. Soil should clump when squeezed, but not be sopping wet.

3. Loosely transfer moist soil mix into seed starting tray or pots.

4. Drop tomato seeds onto surface of soil and then plant as shallow as humanly possible. You may use a toothpick or other tool to push seed slightly under the surface of the soil. Alternately, sprinkle a fine layer of dry seed starting mix and then mist with a clean spray bottle full of water until moist.

5. Cover surface of seed starting tray with clear plastic lid (if provided) or loosely tent with plastic wrap and set in a warm (not hot) place with a temperature from 55-75 degrees. Plastic cover should not be airtight.

6. When seeds begin to germinate, remove plastic cover and move tray/pots under fluorescent lights at a distance of no more than 1-2 inches from bulbs for 16 hours a day. There is no danger of your seedlings being burned if they touch the bulbs.

7. Every day, raise lights or lower pots/tray as needed to maintain a distance of no more than 1-2 inches between leaves and light bulbs.

8. When seedlings have their second set of true leaves, apply liquid fertilizer at half strength mixed in a clean chemical-free spray bottle (ie 1/2 tsp in a 20 oz spray bottle full of water).

9. If your seedlings are in trays, then you will need to transplant at 3-4 weeks into pots. This should happen when seedlings have their third set of true leaves , and are  approximately 3-5″ tall. When transplanting, retain some extra plants as “backups” in case a frost damages your initial planting.

10. Once seedlings are 5-7 weeks old, they should be approximately 8-10″ tall. At this point, it is now 1-2 weeks prior to the scheduled planting time. You should begin “hardening off” your seedlings by gradually exposing them to sunlight, first with full shade, then a few minutes of sunlight a day, gradually increasing their exposure until on the 7th or 8th day, they are experiencing full sun even in the hottest part of the day (11am-1pm).

11. When weather forecasts are predicting no upcoming nights below 40°F, transplant tomato seedlings outside into your garden as deep as possible, removing any leaves that will be buried. This should take place on a cloudy day, or in the mid-to-late afternoon to allow plants 1 day to acclimate. In case of full sun, a sheet or row cover may be draped over sticks, cages, or other framework to shield the plants from full sun for a few days.

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Advanced Seed Starting

Now we will extrapolate and provide more detailed explanations for the Seed Starting Steps provided above.

The Right Soil

When they first germinate, tomato seeds are vulnerable to any bacterial or fungal spores which might be present in your growing medium (soil).

Problem: If shortly after they germinate, your tomato seedlings die, especially with a dark ring just below the soil line, this is damping off and indicates that your soil is somehow contaminated.

Solution: To prevent your seedlings from getting these diseases, seed starting materials should be as sterile as possible.

Seeds should be sown in soil-less seed starting mix which retails for $4~5 foran 8 quart bag which will comfortably fill a 72 cell flat tray or a dozen 4″ pots. You should absolutely not start seeds in potting mix and certainly not garden dirt.

If you have any doubts about your seed starting materials (trays, pots, trowel), sterilize them with a 10% bleach spray and rinse them before use.

If you intend to grow completely organic transplants, then you will need to create your own soil mix from organically-derived peat moss, vermiculite, and perlite. Commercial seed starting mix includes a wetting agent which allows the peat moss to absorb water. If you are creating your own mix, you will need to add 1 tsp of an organic dish soap to 1 gallon of water to encourage the normally hydrophobic peat moss in your mix to accept water.

We recommend pouring your seed starting mix into a large bowl and then pre-moistening it with water until it is just damp, but not sopping wet. Scoop the moist mix into your seed starting trays or pots.

Trays, Pots, and Peat Pots

Whether you start your tomato seeds in trays (sold in a variety of configurations and sizes) or pots is up to personal preference. You may start your tomato seeds directly in 4″ pots and transplant directly into the garden, or you may start in small cells and “pot up” into 4″ pots as they grow taller.

Ferry-Morse sells good quality seed-starting trays with clear plastic domes. These trays can be cleaned and re-used for many years. To save space, you may plant 2-4 seeds in each cell of a 72 cell seed starting tray. They will need to be separated a few weeks later before the roots intermingle. You can also start directly in 4″ pots and just pick the strongest seedling and cull the rest.

The benefit of starting in a smaller cell and then transplanting or “potting up” into a larger pot is encouraging the initial tap root (which goes straight down to the bottom of the pot) to become a more fibrous root system taking up the whole pot.

Problem 1: Seedlings in peat pots do not get enough water causing them to wilt, and do not show healthy growth.

Cause 1: We have found that the compressed peat of peat pots tends to wick water away from the tender seedlings, depriving them of water. Also, peat pots does not degrade nearly as quickly as the advertising would indicate.

Solution 1: Use plastic containers instead, and reuse them year-to-year. After 5 years I have thrown less than 1% of my pots away.

We recommend making a map of your seedling tray (including some indication of orientation in case you rotate the tray and forget which end is which!) and labeling the contents. [Downloadable Seedling Maps]

Problem 2: Seedlings started in peat pots which have been transplanted into the garden fail to thrive and stay stunted.

Cause 2: We have heard stories of frustrated gardeners digging up stunted plants that never broke free of their peat pot prisons.

Solution 2: If you intend to use peat pots, we recommend cutting off the bottom of the pot before transplanting outside to allow free root growth.

Pre-soaking Seeds?

An entirely optional step in seed starting is to pre-soak your seeds before sowing them. Pre-soaking seeds can increase germination % and seedling vigor.

Problem: I have tomato seeds which are over 6 years old. How do I increase the chance of germination?

Solution: Pre-soak seeds in a warm tea & fertilizer mixture for 1-12 hours before sowing.

Add a tea bag to a cup of warm water and steep for 5 minutes. Discard the tea bag and add a few drops of Maxicrop liquid seaweed. Arrange several small bowls or cups, add your seeds to each cup, and then add enough of the weak tea to each bowl to moisten the seeds. Soak seeds for anywhere from one to 12 hours. Then sow seeds into moist seed starting mix.

If you have fresh seeds (less than 5 years old), or you are starting seeds for too many varieties for this to be practical, than this step can, of course, be skipped.

A Matter of Depth

Tomato and pepper seeds, especially cherry tomato seeds, seem to germinate with a higher rate of success when sown extremely shallow — merely 1/8 to 1/4 of an inch deep.

Problem: Tomato seeds, especially cherry tomato seeds, fail to germinate.

Cause: Seeds have been sown too deep.

Solution: Sow tomato seeds extremely shallow.

If you are concerned that you may plant your seeds too deep, then simply drop the seeds on top of the soil and use a small tool such as a toothpick to move a few strands of the peat moss mix over the seeds. Another solution is to drop seeds on top of the moist soil, sprinkle a small amount of dry soilless seed starting mix on top and then mist the surface with a sterilized water bottle until damp.

Tomato seeds germinate at different rates. Cherry tomatoes can be especially precocious. Pepper seeds meanwhile prefer to germinate about 10 degrees warmer than tomato plants (ideally 85 F degrees). If you are lucky enough to have a seedling heat mat, then you can start both pepper and tomato seeds at the same time. Otherwise, we recommend starting your pepper seeds 2-3 weeks before you start your tomato plants as they will need the additional time to come out of hibernation.

How Much Water?

Once you’ve got your seeds planted, your biggest challenge may be resisting the temptation to overwater. We recommend not watering the soil again until the seedlings are 1-2 inches tall and have used up most of the water in the soil. This is typically 5-7 days after germination. There will be a noticeable lightening of the surface of the soil as it dries out. Also, the seed starting trays and/or pots will lose weight.

Don’t let your seedlings dry out either. If seedlings start to wilt, you should water them immediately.

When adding water to trays, we generally prefer “bottom watering“, or lifting the corner of the tray insert and adding water to the tray underneath. This way, tender young seedlings are not disturbed by adding water.

Some minor growth of green moss on the surface of your seed starting trays is normal, but this may be a symptom that you have been overdoing it on the watering.

Get Your Light On

We recommend growing your seedlings under a fluorescent light fixture which accommodates two 48″ 32W or 40W bulbs. These typically run $20-30 at Home Depot and Lowe’s. Given a choice, you should buy a light fixture with the widest metal reflector available so as to distribute the light over the entire width of the tray. The $15 lights at Wal-Mart are of poor quality so we do not recommend them.

The human eye has a remarkable ability to allow us to see comfortably from the light of just a few candles, to the full intensity of the sun.

• Bright Sunlight: 110,000 lux
• Shade: 20,000 lux
• Fluorescent light: 500 lux
• Sunrise: 400 lux
• Full moon on a clear night: .25 lux

Brightness is not just a function of the intensity of the light, but also the distance from the light. For this reason, trying to grow seeds on a windowsill or located 6-8 inches from a fluorescent light is not much better than providing no supplemental light at all. Especially with fluorescent lights, light intensity output falls off dramatically over a distance of just a few inches.

Problem: Tomato seedlings are growing “leggy” and thin, or bending towards a window in search of light.

Solution: Place fluorescent lights no more than 1-2 inches from top of seedling leaves for 16 hours per day.

We recommend raising and lowering either your lights or seedling trays/pots such that the top leaves of your seedlings are no more than 1-2 inches from the fluorescent bulbs. Use chains to raise and lower the lights, or use old books, DVD cases, etc. to raise and lower plants. There is no risk of plants being burned as the bulbs are only slightly warm to the touch.

We recommend running these lights on a timer for 16 hours a day, but if you will be away for a weekend, seedlings can be grown under 24 hour light for a few days without ill effects.

To provide a full spectrum of color, we recommend using one cool white bulb (approximately $4) and one Daylight warm/natural light bulb (approximately $6). Fluorescent bulbs show a marked drop-off in light output after 2 years, so  we recommend replacing them on this interval. There is no need to purchase expensive Aquarium, Terrarium, Deluxe, or Plant Growth lights.

A recent development in seed starting involves High Pressure Sodium and Metal Halide lights. These can produce in excess of 400 W of light. With the use of reflective mylar (the shiny material which party balloons are made of) and with the lights 3-4 feet above the plants, a very large number of plants can be supported. If there is interest in this subject, we can expand on it in a separate article.

It’s a Breeze

Use an oscillating fan to provide a gentle breeze over your seedlings for several hours per day. This will encourage them to grow thicker stems and overall stockier plants.

Problem: Tomato seedlings are not growing thick stems.

Cause: Commercial greenhouses use chemical growth inhibitor sprays which encourage seedlings to grow thick, stocky stems.

Solution: You can thicken the stems of your seedlings by using an oscillating fan.

NOTE: Many major retailers do not carry oscillating fans in December-February as they are a seasonal item. Purchase them now!

Fertilizing Your Seedlings

Emerging tomato seedlings will first show two slender rounded leaves called cotyledons. Sometimes these are attached to the coat of the seed they germinated from. You may use a moist Q-Tip or gingerly use a pinching movement with your fingers to rescue your seedlings from these stubborn seed coats.

The next set of leaves are the “true” leaves s0-called because they are the type of leaves your tomato plants will be growing. Each tomato variety has leaves which are slightly different.

Until you see a second set of true leaves start to emerge (seedlings will typically be 3-4″ tall at this point), it should not be necessary to apply any type of fertilizer. We recommend preparing Maxicrop seaweed/kelp emulsion or fish emulsion at half their normal strength (1/2 tsp per 1 liter) in a completely clean spray bottle which is free of any chemical residues.

Unless you intend to grow your seedlings beyond the typical 6-8 week timeline (producing 8-10″ tall seedlings), this should be the last fertilization your seedlings need until they are ready to be transplanted into the ground.

Potting Up (Transplanting)

If you started your seeds in trays, then you will need to transplant up to 4″ pots when the plants have reached a suitable size, typically 3-5″ tall and with their third set of true leaves. Your seed starting tray should be well-watered about 30 minutes before transplanting. Tomato plants are very risilient and if they’ve had a good drink of water, they’ll stand up well to the transplant process.

Tomato plant stems have many fine hairs which have the remarkable ability to become roots if buried. Take advantage of this by transplanting your tomato seedlings as deep as you can. We recommend picking off any leaves that will be buried in the soil by this process. If the seedling is not tall enough to have leaves above the surface of the soil, then add some soil to the bottom of the pot prior to transplant.

Hardening Off

Seedlings started under artificial light must slowly become acclimated to sunlight before they can be transplanted into the garden. Mid-dayhours of 11am-2pm hold the most brutal sunlight of the day and exposure should be avoided until plants have been suitably prepared. Noon is the time which is most likely to damage tender plants.

1 – 1 1/2 weeks before planting, your seedlings can be moved outdoors into full shade for 1-2 days and then gradually provided with dappled or direct sunlight on a gradually increasing duration. If evening temperatures are predicted to fall below 45 degrees or high winds are predicted, move seedlings indoors. Hardening off times can be doubled on cloudy days. Here is a general hardening off itinerary:

[Day 1] Full Shade
[Day 2] 10 minutes of morning sun.
[Day 3] 15 minutes of morning sun. 10 minutes of afternoon sun.
[Day 4] 45 minutes of morning sun. 30 minutes of afternoon sun.
[Day 5] 1 1/2 hour of morning sun. 1 hour of afternoon sun.
[Day 6] 3 hours of morning sun. 2 hours of afternoon sun.
[Day 7] 4 hours of morning sun. 3 hours of afternoon sun.
[Day 8] Ready to plant.

We realize that many folks cannot do the type of “babying” described above.  There are several methods of unattended hardening off, including placing some type of protection, such as a lawn chair, inverted laundry basket, or lumber supported by bricks or five gallon buckets directly over the plants will allow morning and afternoon sun to reach the plants, but block the searing midday sun until your plants are ready for it.

A solution of kaolin clay powder (marketed as Surround) mixed with water may be sprayed onto plants to provide a protective physical “shell” to reduce sunlight exposure. This sunblock would need to be reapplied in case of rain. Seedlings may also be placed outside under a 50% shade cloth if you have a means to support this cloth over the plants. At the very least, tomato seedlings should be exposed to dappled shade as much as possible leading up to transplant.

Plants which have not been hardened off will exhibit foliage damage 1-2 days after exposure. A characteristic dessication of the leaves from improper hardening off (tan smooth spots where the leaf has dried out and become paper-thin) can stunt or kill seedlings.

Going Outdoors

Tender seedlings are vulnerable to insect pests as flea beetles and leaf miners. Flea beetles leave behind tiny holes in the leaves. Leaf miners leave zigzagging tracks in the leaves of the seedlings. In both cases, there is no point in spraying the plants with insecticides as the insects which caused the damage are gone by the time you find evidence.

Pre-emptively spraying plants with Surround or dusting the plants with Sevin (carbaryl) when they are first set out will protect them from most opportunistic insects.

When to Plant?

The most common question about growing tomatoes in South East Texas is when to plant.

If we wait until all danger of frost has passed (mid-April), then we will get very few tomatoes, especially from late season varieties (most heirlooms). So we must plant out large, healthy transplants in early- to mid-March and be willing to protect our plants from the occasional cold temperatures.

Most of your tomato fruitset will typically occur in late March (if you were able to get your plants out early), April, and early May. By late May to early June, evening temperatures are no longer dipping below 70. Combined with the high humidity and “muggy” conditions” inhibit your tomato plants from setting fruit. Daytime temperatures in the low 90’s also denature the pollen in tomato blossoms, putting an end to any further tomato fruitset.

It is really imperative to get plants out as early as possible and be willing to protect said plants with shade cloth and other measures. Waiting until April is not an option!

Don’t Trust the Weatherman!

Seedlings in containers or pots should be brought indoors if evening temperatures are predicted to go below 45°F or if high winds are expected.

CAUTION: The High and Low temperatures provided by many television newscasts, newspapers, and websites can be very misleading. They do not always indicate the highest and lowest temperature per day, but instead measure a 24 hour period from midnight to midnight. The coldest time of day may be 6 AM.

We strongly recommend consulting the National Weather Service, or Weather Underground to get hour-by-hour predictions of expected temperatures for your area (ZIP code). Weather Underground is usually pessimistic (they always low-ball evening temperatures) which makes it an especially valuable website for farmers and gardeners.

We recommend planting tomato seedlings outdoors when overnight temperatures are forecast to remain above 40°F for the next 3-5 days. After planting your tomatoes outside, we recommend consulting a trusted weather website daily until mid-April. For the last 5 years, we have had at least one unexpectedly cold night (below 40°F) in early to mid- April.

In the event of a predicted frost (below 38°F), immediately install row cover, blankets, walls of water, or tarps during the day to trap as much heat as possible. Plastic coverings should not be allowed to touch plants as they will burn/damage the plants when the cold sets in.

If you have too many plants to protect using the above methods, then constant misting with water from a hose or use of sprinklers has been shown to keep plants from succumbing to frost damage as low as 33°F. City and well water are typically over 40°F and so will provide a temporary “temperature blanket” effect. This solution will increase the amount of fungal problems during the season (specifically early blight), but it is worth it if your plants can be saved.

If plants are lost due to cold, you will be dependent upon “backups” or, as a last resort, the last remaining plants marked on clearance at the local nurseries.

Planting Dates

Exact planting dates change from year-to-year, because weather is so variable. However you cannot wait until the risk of frost is gone. We recommend that you start watching the weather and plan towards certain dates, but always be prepared to delay.

We’ve got a separate article on Tomato Growing Timeline & Gardening Calendars.

This sounds complicated! Can I buy plants?

If you have reached this point of the article and the idea of starting your own tomato seeds sounds daunting, or the calendar on the wall indicates the month as February, you’ll be surprised to know that there are excellent nurseries in the major S.E. Texas cities and surroundings which carry a wide variety of healthy plants. Although I start my own seeds every year, inevitably I do buy a few plants at local nurseries to support local business. Sometimes  they have a great variety I hadn’t thought of. You can safely assume that plants from local nurseries have already been hardened off and are ready for transplant.

Houston – Inside Beltway 8: Wabash Antiques, Another Place in Time, Southwest Fertilizer and Buchanan’s Native Plants all have an excellent array of tomato and pepper varieties.

Houston – Outside of Beltway 8, RCW Nurseries is starting to carry a good selection of herb and vegetable plants. Cornelius Nurseries, Houston Plants & Garden World and Houston Garden Centers all carry the ubiquitous Chef Jeff’s line of tomato and pepper plants which have some good choices.

Austin – Bloomer’s in Elgin, TX has a fantastic selection. We are currently inquiring about additional nurseries in San Antonio.

San Antonio – We are currently inquiring about the best nurseries in San Antonio.

Dallas/Ft. Worth – Calloway’s Nurseries has nearly 20 locations in and around Dallas, Fort Worth, and Plano. We have not investigated, but presumably they have the Chef Jeff’s line of plants which have some good choices.

Revised: 2010.08.23