Growing in your Greenhouse: Tomatoes

Sweet, tart, tangy, acidic, slightly sour or sometimes perfectly balanced. These are the classic tenants attributed to the humble, yet mighty tomato. From sauces and dips to taking the center stage as one of the main ingredient in things like caprese salad, tomatoes are an incredibly versatile kitchen staple. I’m sure by now you know what to do with them once you’ve got them cooking wise (seeing as this is not a cooking blog), but have you yet mastered how to grow them? They seem simple enough, but these beauties can prove to be rather challenging to grow on your own. Not only is the physical act of growing them rather time intensive, but the planning and know how involved can be quite intensive. Pay too little attention and you might lose your crop. Too much water, there goes that pasta sauce you were planning. Cold snap, so sorry there go your sungolds. Did you start all your plants at once and now you have an excess of tomatoes? I don’t see much of a problem there, but some might and that’s okay! We don’t all love to make and jar pasta sauce. Well, luckily for you, I’m here to help (or at least attempt it) by providing some advice and tips to help you plan and execute the perfect greenhouse tomato crop.

First things first, we need to get one thing straight. Not all varieties of tomato are well suited for growing in greenhouses, generally speaking smaller varieties are better suited for environments with less soil. Depending on how you plan to set up and maintain your greenhouse, plum tomatoes grow in a different environment than grape varieties and even beefsteaks. But whatever you plan to grow, some planning should be done prior to starting your garden. Prepping your greenhouse to house your chosen variety can take some prep work. Many tomatoes grow in a vine like plant, but often times the “vine” structures are less than strong enough to support the weight of the fruit while they ripen. Establishing the proper structures and supports for your chosen varieties will go a long way in helping your crop succeed. Cherry and grape tomato varieties are very well suited for places with limited soil space or just space in general. They generally don’t require as much support as the larger variety fruits, but having supports is never a bad idea, especially if you plan on venting your greenhouse and winds are a common theme. Plum variety tomatoes will require more support to grow successfully as their fruits tend to be a bit more bulbous and oblong. Their vine structures can be prone to droop and break even without strong winds, so make sure you steak them accordingly. If you are attempting larger varieties such as beefsteak of heirloom types, make sure you have as much support for it as you can find. These fruits tends to be very large and can bend the vines with ease. All plants will generally grow stronger given a constant breeze is helping to build up the basic structure. The stems of the plants will become thicker as the breeze builds up its strength, however, in your greenhouse wind is likely to be at a premium. If you have fans, it’s not a bad idea to point them at the base of your plants for at least a few hours a day to help strengthen your stalks. Once you’ve gotten your support systems all planned out and taken care of, it’s a matter of starting up your seedlings.

If you’d like to give yourself a head start, invest in a seedling heating mat. While this is not a required step, it will help you along quite a bit. The heating mat will keep your seedlings nice and warm during their incubation process which can help speed along germination. Not only will this handy tool help speed along your growing process, it can help cut down on your heating costs as you don’t need to constantly pump heat into the whole greenhouse. Plant leaves can tolerate a bit of cold, but the root systems are very frost sensitive and if they get cold, your whole crop could be ruined. Once you’ve gotten your seedling heat situation handled, you need to worry about the ambient temperature of your greenhouse. Your tomatoes will grow their best if you keep your greenhouse at 70-75°F during the day and no lower than 60°F during the night. This might increase your heating costs a bit, but so likely will any growing venture you undertake during the summer. If you want to ensure your root systems stay warm after the germination process but don’t want to spend a fortune on heating, you can ensure the heat in your greenhouse is staying around plant height. Heat has a tendency to rise so investing in a heat saver fan to keep your heat where it needs to be. Again, not entirely necessary, but this device will help keep the heat in your greenhouse down around the plants and not congregating near the ceiling. Tomatoes grow best when the temperature is relatively constant, so try not to raise or drop the temperature too frequently or drastically.

Now that you’ve planned out the support system and have your heating under control, you can worry about the water aspect of your tomato journey. A good rule of thumb is to over water your plants to begin with, but then to not water them again until the soil is dry. Over watering tomatoes, like with any other plants, can wreak havoc on your crop. Too much water can result in root rot and a myriad of other problems that will result in you not having tomatoes in the end. If you are worried about your plants not getting enough moisture between your watering events, misting is a great way to supplement water without over exposing the root system. Misting distributes the water evenly which can help prevent over watering as well as use your water more efficiently. When you are watering, take care to keep excess water or wet soil from getting on the leaves as that can lead to disease down the road. It is best the water plants during the morning and make sure you stop watering 2-3 hours before the sun goes down and your plants stop receiving light. If you have access to an irrigation system such as a drip watering system or otherwise, it might be a good idea to use them as they can prevent human error when it comes to watering plants. Get distracted for a second and you can easily tip your watering can too far and flood your plants, we’ve all done it, I won’t judge you. Watering, however, isn’t your only issue.

Lighting should be the next concern on your list. Tomatoes require a ton of sunlight and not getting enough can be devastating to your crop. Not to mention, all that light (sun or otherwise) can help keep your plants warm during the cold months. Again, be sure to keep track of the ambient temperature in your greenhouse to make sure your plants are staying warm and happy. Your plants should get anywhere from 8-10 hours of sunlight to make sure they are getting their required nutrients via photosynthesis. Think about the sun your plants gets outside during the summer when the daytime hours are long, now try and replicate that, just inside your greenhouse. It sounds easy to set up, but it can be somewhat difficult. Ensuring your greenhouse is in the right spot to receive proper winter sunlight is probably the most important thing you can do. Aside from that, if you need to use artificial lighting you would do well to make sure the lights are properly installed in your greenhouse and set to the correct height so that your plants get enough light, without the lights being too close to the leaves.

Once you’ve gotten those intangibles down, it’s time to worry about feeding. Your tomatoes will need a sophisticated mix of nutrients if you want them to grow nice and big. Compost is a great way to jump start the fertilization process, especially if you mix it into the soil prior to planting. This will not only evenly distribute the nutrients that the compost brings, but it will also break up the soil so that the roots have an easier time developing. If you are transplanting starts to a bed of soil, dig a hole and fertilize it up to an hour before you plant your start. This will ensure the fertilizer is applied directly to the developing root system to give it as much a boost as possible. Pro tip, your tomatoes love a phosphorus high fertilizer. Test your soil prior to using fertilizers however as it isn’t generally a good idea to over serve your plants any one nutrient. Make sure your fertilizer will provide your plant with a solid balance of potassium, calcium, nitrogen and magnesium. Feed your plants before you plant them, when the fruit reaches about a third its final size and then once again when the fruit has been picked. Apply the final two fertilizer feedings about 4-5” from the stem of your plants to prevent them from being burned.

Once you’ve gotten all this taken care of, you’re ready to sit back and watch as your plants grow. They will more than likely take care of themselves once you take the proper steps. Make sure you watch how much water they are getting, too much isn’t good and neither is too little. Too much nitrogen in your fertilizer may help you with growing bigger leaves, it more than likely will lead to less fruit. Plan when you plant! I don’t think I can stress this enough. If you plant all your tomatoes at once, you’ll end up with more fruit than you can handle. Nothing smells worse than rotten tomatoes… As with any venture, watch for pests and disease. Both of these blights can ruin your harvest if you aren’t careful. Most importantly, make sure you have fun! Gardening is a fun hobby and can provide health benefits as well as leave you with wonderful food to eat. I hope you found this article informative and helpful in your quest to grow tomatoes. Thanks for reading!