3 Tips for Potting Up Tomatoes

Tomato season is almost here...!! But before you can enjoy all those juicy heirlooms, you'll need to follow a few simple steps to give your little tomato plants the TLC they need to thrive.

This will be my third season growing heirloom tomatoes from seed, and it's certainly come with a lot of trial and error. 

My first year growing tomatoes ended up being a surprisingly huge success, resulting in four monster plants and more tomatoes than I knew what to do with. I’ll admit, I became overly obsessed with these tomatoes, like the protective plant mama I am, but hey, it worked! Even in their giant 20-gallon containers, they made the move with me to my new house with their own protected section in the U-Haul. All the other gardeners out there will understand - you can’t leave your plant babies behind! 

The key to my success was consistently following the tips I’ll share with you below. As much as I’d like to say I just let them do their own thing, tomatoes can be a bit testy and require a lot of care and attention to thrive to their full potential. After potting up my seedlings twice, they established extensive root systems and were well prepared for their new life in the 20-gallon containers. I made sure to start them early, at the end of March, so they were producing full-size tomatoes by June. In addition to fertilizing, the real key was consistent watering. 

Last year, the summer craziness took over, and I became a bit of a lazy gardener. I neglected to follow the tips I'm about to share with you, and it showed. I started my seedlings way too late, didn't use a seed starting mix, never potted them up, watered them inconsistently, and never fertilized them. Tomatoes are hardy plants, so they still gave me a decent crop of lovely little heirlooms, but the differences between my first and second tomato growing seasons were obvious. 

Because I never potted them up, they had weak root systems and became leggy and unstable, the inconsistent watering yielded split fruit, and because I didn't start them early enough, my harvest was later and less than if I'd started them earlier in the season. 

Needless to say, I am determined to redeem myself this summer. My goal: beat the success of my first growing season and achieve bigger, better harvests and huge, healthy plants. 

Tips for Potting Up Tomatoes

Tip #1 - Soil matters!

Use a seed-starting soil mix with mycorrhizae. These are designed to give young plants the nutrients they need to get off to a strong start, and the mycorrhizae support strong root development. Pre-water the soil before planting your seeds or potting up your seedlings.

For the last year or so, I’ve been using Dr. Earth’s Organic Seed Starter Potting Mix for all my seedlings and have been super happy with the results. In addition to lots of nutrients derived from organically composted food products, this mix contains beneficial soil microbes and mycorrhizae to give the seedlings an extra boost. 

If you're potting up multiple times and your plants are substantial in size and well-established, you can mix an organic potting mix with the seed-starting soil. Make sure whatever potting mix you use is formulated for raised bed vegetable gardening and contains all the nutrients your plant needs. My all-time favorite is the Recipe 420 potting mix. It consistently gives amazing results and is loaded with high-quality organic nutrients. That being said, it's on the pricier side, but for something like potting up tomato plants, it's the perfect option since you really won't need that much soil.

Tip #2 - Plant your seedlings DEEPLY.

This is super important as it promotes a strong root system for your growing tomato plants. You know all those funny little hairs the tomato plant grows on its stem? Those are actually potential roots! So the more of the stem that’s planted early on, the more roots the plant will develop, and the stronger it will become. 

When potting up, you’ll want to bury the entire stem up to the first set of main leaves. If your seedling is larger and you’ve already potted it up once, you can remove the bottom set of leaves to expose more of the stem for planting. Roots will also shoot out from wherever you take off leaves. Repeat this when transplanting into the garden later on to continue promoting strong roots.

Some gardeners swear by planting their tomatoes sideways and burying the entire vining stalk so that it grows horizontally along the soil. Wherever the stem touches the soil, it will shoot out roots. This method yields tons of roots for a really strong plant and can be a great option if you have the space. My space is limited (although I’ve made the most of it by packing in as many plants as physically possible), so for now, I’m sticking with the vertical method. But if you have lots of space, it is a highly recommended method to consider.

Tip #3 - Water well and often from the bottom up.

This one may seem obvious, but these baby tomatoes will need lots of water to establish themselves in their big new homes and prevent shock. Plus, seed starter cells dry out quicker than if they were in the ground, so make sure they are consistently moist. 

For the first week after potting up, you can water from the top to ensure the roots get the water they need, but after this, start watering from the bottom up using a tray. This will encourage the roots to grow deeply to reach the water, leading to a stronger root system. 

The watering needs will continue to be high once you transplant your tomatoes into the garden. Consistency is key! They don’t like too much water, and they don’t like to dry out. Depending on your climate and the conditions, you’ll have to gauge how fast your plant is drying out. An easy way to do this is to measure the moisture in the soil with your finger, about 2-3” deep. If it’s dry, it needs water; if it’s wet, wait it out. Create a watering schedule once you figure out how long it takes your tomato plants to dry out. During my first growing season, I watered every other day around 9 am and either skipped a watering if it rained or added a watering in between if it was excessively hot. If you have a drip irrigation system, this is a great way to ensure consistent watering. 

Again, watering may seem like an obvious tip, but how you water and how frequently you water your plants makes a huge difference, so be consistent! 

If you follow these tips for potting up tomatoes, there’s no doubt you’ll have happy, healthy plants to transplant into the garden. Just stick with it and do your best to set yourself up for success. A little TLC in the early stages goes a long way, and your plants will be thanking you with lots & lots of juicy tomatoes! 

Stay tuned for more tips on transplanting your tomato plants and setting them up to thrive in the garden for a successful growing season!