What to Grow in the Greenhouse in January

Greenhouse gardening opens up a mountain of possibilities. If you want pineapple growing in a cold climate or want to turn your desert garden into a tropical paradise, a greenhouse is the answer. 

If you’re living in northern climates, you may need to add extra grow lights or a seedling heat mat. It also helps to grow cold-hardy plants that can stand up to the outside cold. If you live in southern regions or have a greenhouse heater, the varieties you can grow are endless. 

If you’re just getting into greenhouse gardening, the January is the perfect time to start planting. From cold-hardy vegetables to early-season flowers, these are the best plants to grow in your greenhouse in January. 

Chili Peppers

	botanical name Capsicum annuum
	sun requirements Full sun
	height 8”-2`
	hardiness zones 4-12

Did you know there are thousands of varieties of chili peppers? They’re originally from Central and South America. Since traveling around the world as one of the star crops of the Columbian Exchange, they’ve taken on endlessly new shapes and colors. 

Cultivators are constantly trying to grow the hottest, meanest chilis imaginable. This diverse species includes the popular bell pepper, jalapeño, habanero, and ancho. You can also grow one of the tens of thousands of cultivars available on the market. No matter what variety you want, you can find them in seed packages. 

The chemical capsaicin is what triggers the sensation of burning on our tongues and skin. It’s mostly contained in the white pith of the peppers. Not all species are spicy, and many, such as the common bell pepper, have little to no detectable capsaicin. 

If you have a greenhouse with plenty of heat, you can sow pepper seeds in January. You’ll get big, juicy fruits by late spring to summer, depending on the variety. These plants need plenty of sun, water, and heat to thrive. 

Onions

	botanical name Allium cepa
	sun requirements Full sun
	height 6-18”
	hardiness zones 5-11

Onions are a diverse and easy-to-grow crop that’s suitable for a greenhouse. You’ll need large containers and plenty of water to keep the soil moist. Other than that, these versatile vegetables are beginner-friendly. 

There are hundreds of varieties and cultivars to choose from, including the common red, yellow, white, and green onions. They can handle a bit of cold weather, so if you live in a mild climate, you won’t need to heat your greenhouse. 

Add a little fertilizer higher in phosphorus in your soil before planting. Look for the higher middle number in the N-P-K ratio. Once they start growing, switch to a high-nitrogen fertilizer. In the spring, you can plant them outside to free up room in your greenhouse for more goodies! 

Geraniums

	botanical name Pelargonium × hybridum
	sun requirements Full sun
	height 10”-3′
	hardiness zones 9-11

Who said you have to stick to fruits, vegetables, and herbs in a greenhouse? Some of the easiest flowers to start in January are geraniums. These brightly colored, big, and beautiful blooms are irresistible. 

Although there are two genera’ that are called geraniums, most seeds and starters come from Pelargonium × hybridum. These popular flowers form bushy clusters of red, pink, or white blooms. They are easy to plant and maintain, making them perfect flowers for newbie gardeners. 

Sow these beautiful flowers in dry soil composed of perlite, compost, and potting soil. Apply a balanced fertilizer and water them when their soil is dry. Keep your greenhouse nice and warm with a heater to get radiant blooms starting in spring. 

Sweet Peas

	botanical name Lathyrus odoratus
	sun requirements Full sun
	height 3’-10’
	hardiness zones 7-10

Sweet peas are hard not to love for their lovely vine-like foliage, flowers, and, of course, sweet and nutritious pods and seeds. They’re both cold-hardy and easy to maintain. Plus, you’ll get a bounty of delicious snacks in the late spring and summer. 

These delicious vines are native to the Mediterranean, but many varieties have become staple crops around the world. There are now more than 150 species in the Lathyrus genus, with limitless varieties and cultivars to choose from. Some are grown specifically for their abundant, colorful flowers. Others for their delectable and nutritious greens.  

Plant these lovely vines in loose, well-draining soil. Give them plenty of moisture and a diluted organic fertilizer once every week or two. You can support them by building a trellis in your greenhouse or letting them wind their branches freely through the structure. 

Spinach

	botanical name Spinacia oleracea
	sun requirements Full sun to partial shade
	height 4”-10”
	hardiness zones 2-11

Spinach is one of the stars of winter gardens, and in your greenhouse, it will thrive! It’s easy to grow and maintain. It also grows fast, so you could get several crops in one year. You can even plant some varieties as perennials. 

These leafy greens contain a multitude of nutrients. Once they’re mature, harvest them for salads, Mediterranean dishes, or smoothies. By starting them in January, you’ll have a crop to harvest for most of the year. 

Sow the seeds in slightly alkaline soil that’s well-draining. Keep the soil moist throughout the growing season. This delicious green can handle cold temperatures, so don’t worry about heating your greenhouse if it’s above 40°F (4°C). 

Cosmos

	botanical name Cosmos bipinnatus
	sun requirements Full sun to partial shade
	height 2-4′
	hardiness zones 2-11

Cosmos are easy-to-grow flowers that can handle cold temperatures and January sowing in or out of a greenhouse. There are around 30 species of these striking flowers in the Cosmos genus. They complement any greenhouse garden and add tons of vibrant colors. 

Grow them with full sun and well-draining soil. Don’t worry about fertilizing these fast-growing plants. Once they mature, they’ll bloom from early summer to fall. They come in a variety of colors and color patterns, such as red, orange, yellow, and crimson. 

You can harvest these flowers or transplant them outside in summer. If you’re a novice gardener, these hardy plants are some of the best introductory flowers to plant. 

Kale

	botanical name Brassica oleracea
	sun requirements Full sun to partial shade
	height 1’-3′
	hardiness zones 2-11

Kales are some of the best winter vegetables to try in a greenhouse. Some varieties grow so fast that you can harvest them within 45 to 50 days of planting. On top of their speed, they’re easy to maintain and can tolerate cold temperatures.

This highly nutritious leafy green vegetable comes in a multitude of varieties. There are curly varieties, short varieties, dinosaur kales, and ornamental kales, which are also quite tasty. Heirloom kales have also become popular for gardeners looking to break traditions. 

To get these vegetables growing strong, use a seedling heating mat and a grow light if you live in northern regions. Sow your seeds in well-draining soil with plenty of compost. Water consistently without waterlogging the soil. As they grow, try feeding them with a slow-release balanced organic fertilizer. 

Lupines

	botanical name Lupinus spp.
	sun requirements Full sun to partial shade
	height 10”-2′
	hardiness zones 4-8

Lupines can be invasive, and they are poisonous, but oh, are they pretty! They also handle cold temperatures. If you have a greenhouse, you can grow them in January without heating. 

To grow them by seed, soak them in water and rub them on sandpaper to scarify them. This breaks off the protective coating and lets the water in to germinate them. This process is usually done by cold temperatures and thawing in nature. With that in mind, a cold period is necessary for germination, so simulate that if your greenhouse is warm. 

Plant them in well-draining, sandy soil. Give them a consistent amount of water. If they get enough sunlight, you don’t have to worry about the cold. They can survive temperatures close to or below freezing. In nature, they create their own soil nitrogen through a symbiotic relationship with bacteria in the soil. Because of this, you won’t have to worry about fertilizing them. 

Carrots

	botanical name Daucus carota
	sun requirements Full sun to partial shade
	height 12”
	hardiness zones 2-11

Carrots are an obvious choice for a winter greenhouse garden. They are easy to grow and will tolerate the cold temperatures of January in a greenhouse. They produce delicious roots and greens that are full of nutrients and flavor. 

These edible biennials are one of the world’s most planted vegetables. Humans cultivated them from wild carrots, which were considered medicinal in ancient Europe. Over the years, the plant mutated into the nutrient-dense root vegetable we know and love today. 

Plant these cool-season vegetables in well-draining soil. Add a lot of compost and sand to make them thrive. You can fertilize your plants with fish emulsion or other organic fertilizers high in nitrogen. 

If you plant them in January, you should be able to harvest them between two to four months. For snacking, try them when they’re young and small. For stews and salads, wait another few weeks until they’re nice and large. Don’t forget that their foliage is edible, too, and full of vitamins and minerals.