Tips for Optimizing Seedling Growth Rates

Tips for Optimizing Seedling Growth Rates

An article by Travis Key from Lazy Dog Farm

In previous blogs we’ve discussed the many advantages to growing your own vegetable transplants. These include being able to pick the varieties you want to grow, having more control of timing, and growing healthier plants that are never stressed. We often get asked when the best time is to begin “seed-starting” for common backyard vegetables like tomatoes, peppers, broccoli, cabbage, and more. Having a hard date for when to start certain vegetable is tough. There are several factors that come into play here, which we’ll describe below.

Let me start by saying that most vegetable transplants will take 6-8 weeks to go from seed to a transplant that’s ready to go in the ground. But this will depend on several of the factors listed below. In some conditions you may be able to grow a viable transplant in 5-6 weeks, but in other conditions it may take 8-9 weeks.

Factors Affecting Transplant “Grow-out” Time


When starting tomato and pepper seeds in the late winter/early spring months, you’re going to need some type of heat for high germination rates. You can’t just set a tray of tomato or pepper seeds outside and expect them to germinate with a little water. These warm-season vegetables will need soil temperatures in the 80s for effective germination.

If you’re growing transplants in a heated greenhouse, you’ll be able to keep the soil consistently warm throughout the germination period. Heat mats can also help with this as they provide consistent heat to the bottom of the seed starting tray — especially when used in conjunction with a thermostat. If the ambient temperature in your home is 72 degrees, you can sometimes get tomato seeds to germinate without a heat mat. But they’ll germinate much faster if the soil is closer to 80 degrees.

As a result, the heat factor will greatly affect the time it takes to grow a viable transplant. If you have ample heat, you can have those transplants ready for the ground much faster. If you don’t have heat mats and are simply sprouting seeds on a table inside your home, you’ll need to plan accordingly and expect those transplants to take longer.


We’re big believers in fertilizing our seedlings with AgroThrive once they have their second set of leaves (also known as true leaves). Not only does fertilization give us a healthier transplant with a biologically active root ball, but it also gives us more control over the growth rate. You can push seedlings as fast as you want, or back off the fertilizer and slow their growth rate.

In some cases, we may have relatively warm late winter temperatures, which means that we can begin warm season planting sooner than later. In other years we may have to delay warm season planting due to late freezing temperatures. But our fertilization schedule allows us to easily manage the growth rate, so we have transplants ready when the outside temperatures are cooperating.

Whether you need your transplants soon or have some time, I always recommend feeding seedlings with AgroThrive at least once a week. If you need them as quick as possible, feed them 3-4 times a week by mixing 1 ounce of AgroThrive with 1 gallon of water. If you want to get aggressive with the growth rates, you can feed them every single day and it won’t hurt the plants.

Container or Cell Size

Whether you’re growing tomato plants in commercial-grade seed trays or plastic cups, you don’t want to transplant them until they have a developed root ball that holds together when pulled from the container or cell. That’s our general rule to tell when a transplant is ready to go in the ground. If it can’t be easily pulled from the container by tugging on the stem, it’s not ready.

We grow our tomato plants in heavy-duty trays where the cells are only 1.5” wide, but many gardeners are resourceful and use whatever they have laying around the house. For the smaller cell trays that we use, we can have a developed root ball much faster than if we were growing tomato plants in a red plastic cup. The larger the container, the longer it’s going to take to have a root ball that’s ready to plant.

Timing is Important!

When gardeners catch the “spring planting itch,” they can’t wait to get plants in the ground. Many backyard gardeners pride themselves on having ripe tomatoes before any of their gardening friends or neighbors. If you follow these guidelines when growing your transplants, you can ensure that you’re one of the first to have tomato plants ready to plant in the spring.

Timing is also important for those living in areas with extreme summer heat. Here in south Georgia, our tomato season is usually done by mid to late July. Tomato plants typically don’t like temperatures in the 90s, and so we’re limited in what months we can grow tomatoes. That’s why it’s important for us to have plants ready to go in the ground as soon as possible in the spring. We want to maximize the number of tomatoes we harvest before it gets too hot, and you should too!

Thousands of gardeners have been tuning in to The Lazy Dog Farm YouTube channel where Travis covers a variety topics ranging from how to successfully start seedlings to how to make a flavorful hotsauce that packs a punch. Accompanied by his wife Brooklyn and their two boys, the gardens on their 2 acre homestead in southwest Georgia are always filled with a wide variety of vegetables that are enjoyed fresh or preserved for later.

1 comment

  • Robert

    Any advice with hydroponics?

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