Greenhouse Growing Guide: Squash and Potatoes

Squash and potatoes can both be grown on a year-round basis in your home greenhouse. You can even use the greenhouse in later winter or early spring to get a headstart on the growing season. 

When to Grow

As a warm season vegetable, squash can be started in your greenhouse in March or April. Making consecutive plantings through May ensures that you won't end up with your squash crop ripening all at once. Squash is generally very easy to grow, but keep in mind that it does require a great deal of garden or greenhouse space. 

Starting the Seedlings

Plant squash seeds about an inch deep in a good seedling-starting mix designed for vegetables. You can generally purchase this from your local home and garden retailer. If not, simply mix three parts potting soil to one part each of medium sand, perlite, and compost. Peat pots work best for starting seedlings since you can just plant them pot and all and they'll decompose into the soil. Most varieties of squash need soil that is at least 65 degrees Fahrenheit in order to germinate, so you may need to use a heat mat. Allowing your seeds to dry out may result in failure to germinate, so make sure you keep your soil moist. 

The seeds should begin to germinate within 12 days, with some varieties making their entrances earlier. Squash grows quickly, so your first seedlings of the season should be ready to be moved to an outdoor garden spot by the beginning of summer. If you plan on growing them in the greenhouse, you can transplant them into 2-gallon pots and place them in a warm, bright location. These containers should be placed at least 4 feet apart. Smaller varieties of squash can easily be trellised upward, but the larger ones are too heavy for this practice. 

Growing Squash

Squash essentially grows itself in the greenhouse environment. In order to prevent fungal pathogens from becoming a nuisance, vent the greenhouse for two hours per day (weather permitting), and make there's plenty of room between the plants. You can turn on a cooling fan or open up the doors when interior temperatures rise above 95 degrees. It may also be necessary to hand-pollinate squash if you're growing it in a greenhouse since you won't have the insect populations to rely on for this necessity.

Female flowers have a large swelling at the base that will later form the fruit, while male flowers have the pollen on their anthers. You should be able to see the pollen clearly with the naked eye. To pollinate the female flowers, gently remove the male flower from the vine, peel back its petals, and place the anthers inside the female flower. Repeat until the female flowers have all been pollinated. They should set fruit within seven days.

Harvesting Squash 

Harvesting squash should be done as soon as you're sure that it's ripe. Otherwise, it loses flavor, takes on an overly hard texture, and becomes extremely seedy. Squash that's ready to harvest is firm to the touch and can't easily be pierced. Summer squash can be picked before fully ripe and will continue ripening off the vine, but winter squash needs to be left on the vine until fully ripe.

Growing Potatoes

Growing potatoes in your home greenhouse is an excellent way to enjoy fresh potatoes year-round, particularly if you like some of the varieties of fingerlings that aren't that widely produced on a commercial basis. Even if you're happy with the kinds of potatoes that are easily found in the supermarket produce bin, there's something satisfying about growing your own — and it's not as hard as you'd expect.

Getting Started

Although it may be tempting to grow your own potatoes using the ones from the supermarket, always use certified seed potatoes from a reputable retailer. Grocery store potatoes may have been treated with anti-fungal preparations you'd be consuming, and they also come with the risk of carrying a widespread disease known as potato blight. 

First, examine your seed potatoes for any sign of decay. Next, carefully cut the larger ones into two or three pieces using a sharp knife. Each piece should contain at least one eye, which is the small nodule on the side of the potato. Smaller seed potatoes can be planted as they are. However, if you make any cuts in any of the seed potatoes, wait about 24 hours before planting them to give them a chance to harden off. Otherwise, they may simply rot into the soil. 

Potato Bags

The best way to grow potatoes in a greenhouse is to use potato bags. These are flexible bags that you can purchase from a garden retailer at an inexpensive price. If you want, you can even use a heavy duty garbage bag to grow your potatoes in. Black bags work better than white because they attract and retain more heat. 

Planting the Tubers

A mixture of potting soil and mushroom compost makes a good growing medium for potatoes. You can also use shredded leaves. Place about 3 inches of either in the bottom of the bag and plant your potato tubers about an inch deep. A one-gallon bag can hold one large tuber or two small ones, while a five-gallon bag holds between three and five tubers. Water them in lightly before placing the bag or bags in the warmest part of the greenhouse. 

Potatoes grow quickly once they sprout, so check their progress every day. When the shoots have reached four inches high, cover them with the growing medium, leaving about an inch exposed, and keep repeating this process until the bag is full. Use a high-phosphorus fertilizer during their growth to ensure optimal production. The potatoes will be ready to harvest after the tops of the plants flower and die back. When this happens, simply upend the bag and pick your potatoes.


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