Choosing Tomato Transplants

You can start tomatoes from seeds, but many gardeners buy seedlings (or transplants) in the spring. Choosing the best transplants will result in tomatoes that rebound quickly from being transplanted, grow vigorously, and yield the best crop. Fortunately, choosing the right transplants is straightforward. Except for one thing, all of the criteria for choosing the best transplants are fairly obvious. 

When looking through tomato transplants at a nursery, your first goal should be to identify the healthiest plants. Yellow leaves, which can often be found among the lowest leaves on the plant, indicate a lack of nitrogen. A purple cast, especially around the edges of leaves, is likely to be a phosphorus deficiency. This is less common than a nitrogen deficiency. Tomato seedlings should be a moderate to dark green — but not blue green, as that is evidence of too much nitrogen. And, obviously, they should not be wilted. Wilting could be due to a lack of water — in which case it is easily solved — but it could also be a sign of more serious problems. Young tomatoes — transplanted into well-drained, fertile soil — can quickly overcome early nutrient or water deficiencies, especially if they are minor. However, it’s best to start with the healthiest plant possible. 

Yellow leaves, most often seen near the bottom of transplants, are a sign of a nutritional deficiency. Deformed leaves may be the result of disease. Transplants can quickly overcome mild nutritional deficits.

When looking at transplants, also look for holes in the leaves, which may be indicative of an insect infestation. The leaf damage in and of itself is not particularly worrisome. However, some insects — such as white flies — carry diseases that can manifest themselves when the plant is larger. Also look for leaves that are curled, blotchy, or malformed, as this may be the fist signs of disease. Avoid these plants. 

The final thing to look for in a tomato transplant may seem counter-intuitive — look for the smaller transplants (among plants in same-sized containers). Tomatoes are often sold in tiny 4-well flats, 4″ planters, or in small cups that hold a little more soil. Much of the time, nursery transplants have overgrown their planter by the time they are on display. They can look healthy, but they are rootbound. Nurseries offer these transplants because people want to buy large plants. They think they are getting ahead that way. If there is a table of tomato transplants at a nursery, you almost always see people crowded around the largest plants.

Sometimes, the plants for sale already have flowers. And people obviously like to buy them, apparently because they think they will have tomatoes soon. However, early flowering is not desirable as it is indicative of the plant having switched from rapid growth to an attempt at reproduction. You may get tomatoes fairly quickly, but they will likely be small and the rest of your crop with not be very abundant. 

When you take overgrown transplants out of their container, the roots will be a tangled mess, pressed against the sides of the container. The above ground foliage can look healthy. However, once planted it will take time for a rootbound to acclimate. They will be slow to start vigorous growth. Rootbound tomatoes will rebound with time, but you are better off starting with smaller transplants. These will quickly start growing vigorously and — if you plant at the right time — be the right size when it it is time to flower and set fruit. 

This plant is roughly twice as tall as its container. Its roots have grown to the sides of the planter, but are not excessively tangled or knotted. It should quickly rebound and resume vigorous growth when planted.

A reasonable rule of thumb is that the transplant should be less than three times as tall as the container it is growing in. Optimally, I think that when a plant is twice the height of its container, it is fairly large, but small enough that it will acclimate quickly when planted. Because it is not rootbound, it was likely growing quickly inside its container. And it will continue this vigorous growth‚ after a very brief period of acclimation — when put in the ground.

That’s really all there is to choosing transplants. Pick a healthy, green plant — one that is small enough that it is still growing rapidly in its container — and you are off to a great start.

Sprouting Tomato Seeds

I have planted my 2023 spring tomatoes over the past two weeks. Standard gardening advice is to plant tomato seeds 6–8 weeks before you anticipate putting the transplants in your garden. The best time for transplants is when all danger of frost has passed and overnight lows are 50 °F (10 °C) or above. For me, it’s now 8 weeks until that time. As such, I planted my tomatoes 1 or 2 weeks earlier than recommended. This is not a big deal. Last year, an early heat wave stopped my plants from setting fruit at what should have been the peak of their productivity. So I wanted to be sure to avoid that this year. 

Tomato seed packets and some tomato seeds. All these varieties are TYLCV-resistant cultivars given disease pressures in my area.

The tomato (Solanum lycopersicum) is a member of the nightshade family (Solanaceae), along with potatoes, peppers, tobacco, petunias, and others. This group also includes the poisonous plants Datura spp. (jimsonweed) and Atropa belladonna (deadly nightshade) — both of which of which I grow in my garden.

Planting Tomato Seeds

Planting tomatoes is very straightforward. To do so, fill your flats with potting mix and shake them to settle the soil. Take your finger and press lightly in the middle of each well of the flat, making a depression roughly 1/8” (0.3 cm) deep. Place one seed in each depression and sprinkle potting mix over each seed until it is covered. Getting the exact depth is not important. If you plant the seeds way too deep, over 1/2” (1.3 cm), the seedling will not reach the surface. Too shallow, and the seedling may fall over. However, anywhere in the ballpark of 1/8” (0.3 cm) will work fine. Another rule of thumb is that each tomato seed should be covered to a depth of roughly 3 seed widths.

Some newly sprouted tomatoes (left) and some slightly older tomatoes (right). When first sprouted, the plants unfurl their two cotyledons (seed leaves); next their first true leaves emerge from the stem, at right angles to the cotyledons.

Tending to Planted Seeds and Seedlings

While the seeds are sprouting, you will need to keep the potting mix damp. Tomatoes will do best when sprouted at 65–85 °F (18–30 °C). This is a wide range and standard room temperature falls within it. A seedling heating mat will bring seeds to the upper end of this range. I used a heating mat and my seeds started germinating on day 5. Of course, warm and damp is an invitation for mold or other fungi to start growing. However, tomatoes sprout more quickly than any fungus can get going, so it’s not a problem. 

Tomato seedlings in flats (left) and in 6″ planters (right). The true leaves have extended to become branches, from which multiple, multi-lobed leaves grow.

I keep the seedlings indoors overnight, where the temperature is 68–70 °F (20–21 °C), but set them out in the sunshine when the temperature outside is above 50 °F (10 °C).  On days when they can’t get any outside sun, they sit by a window and I turn on my grow light. During the seedling stage is when fungi can become a problem. To deter the growth of fungi, remove the flats from the heating mat and allow the top of the potting mix to dry out, or nearly so, between waterings.

In a couple months the plants will produce small, yellow flowers and set fruit. These are tomatoes from last year (2022).

I’m in USDA Plant Hardiness Zone 8B, so my gardening season is going to start a bit before most gardeners in the US. Keep watching this website for more vegetable gardening information. 

Garlic Experiment

One question many gardeners have is whether you can plant supermarket garlic and have it grow successfully. If you search the web for the answer, you get both yes and no. Some people say, “Sure, just stick it in the ground and it will grow.” And this is tempting since seed garlic is expensive compared to supermarket garlic. Others — and especially those selling seed garlic — will say that supermarket garlic may be treated with growth inhibitors or that it may bring disease to your garden. I decided to conduct an experiment to compare the two. 

Supermarket garlic (left): It cost less than $0.65 per bulb. Seed garlic (right): It cost about $18.00 for this bag, making it roughly $5.40 per bulb. The sizes of the seed garlic bulbs, and cloves inside, were bigger than the supermarket variety, however.

Garlic is planted in the fall. In my area, they say that mid to late October is the best time to plant. So, my experiment is already up and running. In one of my 50-gallon planters, I planted both supermarket garlic and seed garlic. Both types were softneck garlic, although they are different cultivars as I couldn’t find seed for the supermarket variety. The seed garlic I planted is called Lorz Italian. Sharing the same planter, both types are in the same type of soil, will get the same amount of watering, and the same amount of sun. I planted the garlic cloves in a grid with alternating types. That way, if — for some reason — one section of the planter was more favorable to growing garlic, both types would be growing in it. That’s not likely, but a good experiment is designed to control for all possibilities.

Everything in the experiment was designed to treat both types of garlic the same way. That way, any differences between them should be due to the experimental variable (supermaket or seed), not to differences in how they were raised. I’ll give more “science-y” details about this experiment in a later post. These will include a discussion of sample size, statistics, and whether this experiment has the power to answer the experimental question. I will also discuss limits to the inferences that can be drawn from the data and more. 

On the left, a picture of the planter after the supermarket garlic was planted, but (immediately) before the seed garlic was. The red markers show where the seed garlic will go. The supermarket garlic is planted to the left or right of the markets, with the spacing being even. The cloves are all separated by 5 inches. On the right, the planter today, with a few sprouts visible.

I planted 10 large, healthy-looking cloves from the supermarket garlic and 10 from the seed garlic. The seed garlic cloves were substantially larger than the supermarket cloves. (I still have some of each type left and will weigh them to get a ballpark difference. I should have done that with the actual cloves I planted, but didn’t think about it until after they were in the ground.) I will assess the germination rate of each type. In the summer, I will give a rating based on how large and healthy the plants look during mid season. I will also reassess at maturity. Most importantly, at harvest time I will weigh the garlic heads to see if one is yielding more than the other. And of course, there will be a taste test. 

I planted both types two weeks ago and they have already started sprouting. (There looks to be a pattern emerging, but I’ll wait until all the data is in before reporting it. For one thing, early sprouting may not be a good sign. Or it might be, I don’t know. However, through the experiment, I have a good chance of finding out.)

Two types of seed garlic — softneck (left) and hardneck (right).

I also have a second garlic experiment running, although this one is not as well-controlled as the first. In a separate planter, I have planted 12 cloves of hardneck garlic, a variety called German White. I want to see how softneck garlic performs vs. hardneck in my neck of the woods. The answer in every garden guide I’ve ever read is that hardneck garlic will do poorly in the south (where I live). But, I’ll find out. 

My hardneck garlic planter. I’ll need to mulch this down before cold weather arrives (if it does).

Gardening As The Climate Changes (II)

Scientists expect that climate change will have a number of effects on our lives. As gardeners, one of the most important of these is a change in the arrival time of spring temperatures. Averaged globally, spring temperatures will start arriving very slightly sooner each year. However, at any individual location, the arrival of spring temperatures — compared to their expected arrival date — will be highly variable. Since spring is more likely to arrive early than late, make a plan to take advantage of this situation.

USDA Plant Hardiness Zones correspond roughly to the last frost dates in those areas. Mountainous regions will have later than expected frosts compared to flatlands. Check the internet to find your local average last date.

Most gardeners are well aware of their region’s average last frost date. Gardeners generally begin planting vegetables and annual flowers once this date has passed and the weather forecast indicates a continuance of above freezing temperatures. In northern gardens, the overall growing season is fairly short. For long-season crops, such as pumpkins, getting them started at the right time will ensure that they develop and reach maturity under favorable temperature conditions. In the south, vegetables needs to be planted promptly so that exceedingly hot temperatures don’t arrive until after the plants have flowered and set fruit. Most vegetables will not set fruit at temperatures over 95 °F (35 °C). As an example, the unprecedented heat in Texas in the spring of 2022 was disastrous to watermelon farmers. (It also did in my watermelons and limited my tomato crop.)

Sometimes it seems like spring has arrived early, but don’t interpret early warm temperatures as an indication that no future freezes are coming. Watch your local long-term weather forecast as your last frost date approaches.

As spring approaches, you should plan to plant when you normally do in relation to your average last frost date. As this time approaches, however, keep an eye on the long-range weather forecast. If your last frost date is still approaching, but the forecast does not include a freeze, consider planting at least some of your spring garden plants. Keep in mind, though, that nearly every year there are at least a few days of comparative warm weather near the end of winter. Every year, this entices gardeners everywhere to set out tomato transplants early only to have them freeze later. Recall that half of all final freezes occur after the average last frost date. So resist the urge to plant over three weeks early. That’s just asking for trouble. Planting early can reap big benefits, but it is also taking a risk. If your last frost date is three weeks away, and the forecast overnight lows are all above 36 °F (2 °C) or so, think about planting the vegetables that will thrive (or at least tolerate) those temperatures. For example, most peas will be fine when planted immediately after the soil thaws. Most beans, however, will do poorly if the soil temperature is lower than 50 °F (10 °C). Lima beans require even warmer soil temperatures and daytime air temperatures should be around 65 °C (18 °C).

Covering plants with cloches, row covers, or by growing them in mesh enclosures allows you to get a jump on the season. They will also keep out pests, but must be removed before temperatures get too high. (Cloche photo courtesy Wikipedia)

If you do plan to plant early, invest in some hoops and agricultural netting. This will allow you cover the rows if a light freeze is forecast. For individual large plants, a cloche can serve as a mini-greenhouse when cold weather threatens. If the plant is only a few inches tall, you can cut the bottom out of a gallon milk jug and use that as protection. Large plants, of course, can be planted indoors in small containers and moved outside when the weather is suitable. Even before climate change became an issue, gardeners had been doing this to raise transplants for spring planting.

You can plant garden plants indoors before it is warm enough for them to be outside. Take them outside on warm afternoons and bring them in at night. Or, keep them by a window that gets sun or under grow lamps.

Among the longer-term effects of climate change will be a shifting of agricultural zones towards the poles. North American gardeners on the southern edge of where growing a typical vegetable garden is possible will find it increasingly difficult, and eventually impossible, to grow anything other than a few locally-adapted plants. Gardeners on the current northern edge of vegetable gardening feasibility will start experiencing longer growing seasons and higher peak temperatures. The line on the map separating places that normally experience at least one hard freeze every year from places that do not usually experience freezing temperatures will creep northward. This line is currently in the very southern tips of Florida and Texas. Gardeners south of this line may experience more insect pests in the early spring as they won’t freeze in the winter. (And of course, some insects are adapted to survive freezing temperatures in the winter.) However, these conditions will not arrive overnight.



So, to make a long story short, expect the change in climate to proceed fairly slowly. (Or at least, it will seem slow from our perspective. On a geologic scale, it’s happening blindingly quickly.) But expect the variability in your local weather to become progressively more pronounced. As a gardener, expect that spring temperatures are more likely to arrive sooner than usual than later than usual. But realize that advance will be sporadic. Most years, your weather will likely stick close to the long-term averages. However, sometimes spring temperatures will arrive substantially earlier than expected. So plan for your usual gardening season, but be prepared to get a jump on your spring planting each year. If the indicators of an early spring are present, the risk of early planting should pay off more often than not.

Gardening As The Climate Changes (I)

Our planet is warming. Carbon dioxide (CO2) levels in our atmosphere have increased from under 300 ppm in the early 1900s to over 410 ppm today. This is mostly due to the burning of fossil fuels. Carbon dioxide acts as a greenhouse gas and the global mean temperature has risen 1.8 °F (1 .0 °C) in the past 20 years. This change in temperature has affected weather patterns all over the globe. On average, what we expect to see in the coming years is an earlier arrival of typical spring temperatures. Likewise, we expect longer and hotter summers, a later arrival of typical winter temperatures, and less predictable patterns of precipitation. The phrase “on average” is very important to understanding climate change. The average rate of climate change for any given location will be very slow, but the effects on local weather patterns will vary in intensity.

Carbon dioxide levels have been rising steadily in our atmosphere for decades. The average temperature at the earth’s surface is also trending upwards, but notice that it drops for short periods, too. Compared to the 20th Century as a whole, we are now between 0.8 and 1.0 °C warmer. (Figures from NOAA.)

In the coming years, your garden is likely to experience spring temperatures sooner than in past years. However, in some years, spring could come later. The chance of the latter is lower than the former, but far from zero. As we’ve seen in the previous decade, peak summer temperatures will usually be higher than usual. In a like manner, typical fall temperatures will remain a bit longer before falling.  In both cases, the opposite may occasionally be true. But those instances with be rare.

On average, this progression will be very slow. It will also vary with location. For example, regions near the poles are warming faster. In addition to changes in the seasonal temperatures, you may experience more or less rainfall than average, depending global weather patterns. You will also likely experience years during which your weather is relatively normal.

You can think of climate change this way. Let’s say you had a 6-sided die and you rolled it each spring. The number you got determined your weather. One and two meant cooler than usual weather. Three and four meant average temperatures. And five and six meant higher temperatures. In the past, with a fair die, those three outcomes would have occurred equally frequently in the long term. These days, the die would be loaded. It would be fixed so fives and sixes occurred slightly more often than they should. You could still roll a one through a four, though. You could even roll a series of ones, twos, threes, and fours. However, over time, you’d rack up more five and sixes than any of the other numbers. 

The ten hottest years of all time all occurred in the past 20 years. Nine of the past 10 decades have been warmer than the decade before them. 1940–1949 stands out as a comparatively hot decade. (Data from NOAA and NASA; tables courtesy of Wikipedia)

When it comes to planning your garden, the thing to realize is that the average change in your seasonal weather is going to be very slight. However, the variability in weather patterns will be higher than in past years. Most years, your usual planting schedule should work. However, in other years it might be substantially out of sync with the weather. As such, you may want to hedge your bets. Since temperature anomalies are more likely to be higher than lower, your best bet is to assume that you will experience normal temperatures during the gardening season, but prepare for warmer temperatures. In an upcoming post, I will explain how to do this.

In 2021, some parts of our planet experienced temperatures on par with their long-term average. Much of the Pacific Ocean, for example, was not hotter or colder than usual. And, some of Antartica was slightly colder than usual. However, most places on earth were warmer than usual — especially near the poles. (Figure from NOAA.)