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How to Use Greenhouses to Grow Plants From Seeds

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Though the weather outside might be frightful, you can start your garden early with a greenhouse. Whether you use a cold frame, mini-greenhouse or freestanding unit, your seeds germinate in a warm, comfortable environment that fosters growth. By the time spring arrives, your seedlings will be sturdy transplants, ready for the garden.

Cold Frame

In its simplest form, a cold frame is a shallow pit, often framed in wood, and covered with a glass-topped lid. Generally, the north, or back, side of the frame is taller than the south side. This allows the sun’s rays to penetrate into the interior and warm the seed trays, peat pots or flowerpots. While the temperatures inside a cold frame may only rise to 10 degrees Fahrenheit above the outside temperature, it is enough for cold-tolerant vegetable or flower seeds to sprout. Broccoli, cabbage, peas and radishes are among the seeds that germinate in temperatures as low as 40 degrees, although the optimum temperature ranges from 75 to 85 degrees.

Hotbed Frame

A cold frame may be heated with manure, heating coils or a light bulb, making it a hotbed. To use manure, dig the pit 30 inches deeper than you’d dig a hole for a cold frame. Add 6 inches of coarse gravel to the pit and tamp it. Fill the bottom of the hole with 18 inches of partially composted manure, such as horse manure. Cover the manure with 4 inches of potting soil. Place the lid onto the hotbed and wait until the soil temperature drops to 85 degrees before adding seeds or seed trays to the hotbed. Monitor the soil temperature, and lift the lid if it rises above 85 degrees. If you use heating elements or a light fixture, always plug the unit into a GFCI-protected outlet.

Indoor Mini-Greenhouse

An indoor mini-greenhouse is helpful when your home is drafty or its temperatures are lower than the optimum germination temperature for your seeds. Tomatoes and peppers germinate best between 80 and 85 degrees. While there are commercially available mini-greenhouses, you can use a simple clear plastic container, such as one that strawberries, cherry tomatoes or other fresh fruits are packed in at the supermarket. The clear lid serves as the “greenhouse.” Alternately, you can use any clear container and cover it with plastic wrap to make your own mini-greenhouse.

Freestanding Greenhouse

A freestanding greenhouse allows you to start multiple seeds on shelves or benches, depending on the size of the unit. Add heaters and fans to regulate the interior temperature. Fluorescent lighting adds more light on cloudy days to encourage seedling growth. Before starting the seeds, disinfect the shelves, benches, pots and trays; the warm, moist environment inside the greenhouse makes an ideal climate for algae, fungi, gnats and other pests, as well as your plants.

Seed Starting

Fill peat pots, flowerpots or seed-starting trays with moist seed-starting mix. Plant the seeds according to the seed packet directions, usually two or three seeds per pot at a depth ranging from 1/8 to 1/2 inch. Cover the seeds with soil and mist with water. Cover the pots or trays with plastic wrap. Place them in a warm, brightly lit location. An electric heating mat manufactured for seed starting allows you to regulate the soil temperature. When the seedlings appear, remove the plastic wrap.

Continue to keep the planting mix moist, but not waterlogged. Snip the excess seedlings with scissors; leave one seedling per pot. Fertilize every one to two weeks with a one-quarter strength 5-10-5 water-soluble fertilizer. Water each seedling with 1/4 cup of the fertilizer solution. Water the plants after fertilizing. When the seedlings are approximately eight weeks old, they’re ready to harden off and plant outdoors, weather permitting. Otherwise, transplant them into larger containers so they can continue to grow.

How to Use Greenhouses to Grow Plants From Seeds. In nature, seeds and plants are subject to ever-changing temperatures and weather conditions. For gardeners attempting to grow finicky or troublesome plants from seed, these fluctuating conditions often cause frustration. Many plants have particular requirements before …

Greenhouse Seed Starting – When To Plant Greenhouse Seeds

While many seeds can be sown directly in the garden in fall or spring and actually grow best from natural weather fluctuations, other seeds are much more finicky and require steady temperatures and a controlled environment to germinate. By starting seeds in a greenhouse, gardeners can provide a stable atmosphere for seeds to germinate and seedlings to grow. Continue reading to learn how to sow seeds in a greenhouse.

When to Plant Greenhouse Seeds

Greenhouses allow you to control the temperature and humidity required for seed propagation and young seedlings to grow. Because of this controlled environment, you can actually start seeds in greenhouses anytime. However, if you are starting plants, which you plan to transplant into gardens outdoors in the spring, then you should start the seeds in greenhouses 6-8 weeks before the last expected frost date for your location.

For best success, most seeds should be germinated in temperatures around 70-80 F. (21-27 C.), with night temperatures that do not dip lower than 50-55 F. (10-13 C.). The temperature in your greenhouse should be carefully monitored. Greenhouses are generally warm during the day, when the sun is shining, but can get much cooler at night. Seedling heat mats can help provide seeds with consistently warm soil temperatures. Greenhouses that are equipped with fans or opening windows can vent greenhouses that have gotten too hot.

Greenhouse Seed Starting

Seeds are usually started in greenhouses in open flat seed trays or individual plug trays. Seeds are prepped according to their specific needs; for example, they may be soaked overnight, scarified or stratified, then planted in trays the greenhouse.

In open flat trays, seeds are usually planted in nicely spaced rows for ease of thinning, watering, fertilizing and treating seedling diseases, such as damping off. Then, when these seedlings produce their first set of true leaves, they are transplanted into individual pots or cells.

In single cell trays, only one or two seeds is planted per cell. Many experts feel that planting in plug trays is better than open trays because the plug cells hold and retain more moisture and warmth for the developing seed. Seedlings can also stay in plug trays longer without their roots becoming intertwined with their neighbors. Seedlings in plugs can simply be popped out and transplanted right into the garden or container arrangements.

When starting seeds in a greenhouse, you don’t need to spend a fortune on special seed starting mixes. You can mix your own general purpose potting mix by adding 1 equal part peat moss, 1 part perlite and 1 part organic material (such as compost).

It is, however, very import that any potting medium you use be sterilized between uses to kill off pathogens that can lead to the seedling disease known as damping off. Also, if temperatures are too cool in the greenhouse, light is not intense enough, or if seedlings are over watered, they may develop leggy, weak stems.

Some seeds are finicky and require steady temperatures and a controlled environment to germinate. By starting seeds in a greenhouse, gardeners can provide a stable atmosphere for seeds to germinate and seedlings to grow. Learn more in this article.