GardenLine | Vegetables | Early Bird May Get the Veggies

With each passing day, the amount of energy in the sun's rays increases, and the sun rises higher and higher in the horizon. This results in warmer and longer days, which in turn means the soil becomes warmer. At this time of year, people often ask us: When can I start planting my garden? At what point will the seeds germinate, and the plants start to grow? Below are a few factors to consider in answering these questions.

Soil: Not all soils warm up at the same rate. Clay soils have the ability to hold more water than sandy soils. Water has a high specific heat - meaning it takes a large amount of energy to raise the temperature of water. Therefore, clay soils, with their high water-holding capacity, require a lot of heat to warm them. Clay soils thus do not warm early in spring. Sandy soils are very much the opposite of clays. They hold little water, and thus warm much faster in the spring.

The process of germination for some plans occurs at soil temperatures as low as 2C. Not all plants have the ability to germinate at these temperatures! The process of germination at low temperatures is slow. As temperatures increase, the speed of germination increases. For example, parsnips may take up to 3-4 weeks to germinate at soil temperature of 2C, whereas at 15C they make take only 1-2 weeks. The temperatures referred to are average daily soil temperatures (average of high and low daily soil temperatures).

If you have a garden that is well protected from cool spring winds, the amount of heat the soil collects is higher because the wind will not carry away the heat. For this reason, protected sites tend to warm much faster than open, exposed sites. Most soils have the ability to collect heat during the day and lose it at night. The more heat collected during the day, the longer it takes to release at night.

Environment Enhancement: There are a number of devices capable of increasing the amount of heat the soil is able to collect. Plastic tunnels (mini-greenhouses), hotcaps, cones, and cloches are but a few. These allow the heat to pass through them, but prevent some of it passing back out. As a result, the heat is trapped near the soil, which becomes warmer. Most garden centres sell a variety of these environment enhancing devices.

Vegetables to Try: Not all vegetables can be seeded early in spring. Early-germinators worth trying include parsnip, carrot, onion seed, garlic cloves (possibly onion sets), spinach, lettuce, radish, and may peas (see below). Vegetables such as corn, beans, vines (cucumber, melons, squash), tomato, and pepper are warm season vegetables that will not germinate in cold soil. Try short rows (7-12 cm/3-5 in.) just in case luck is not on your side. Don't put all your eggs in one basket.

Potential Problems: Early spring seeding is not without risk. Seeds will often rot in soils that are both cold and wet. This is especially true for larger seeds with a high sugar contents (peas for example). The faster germination and emergence of the seedlings occurs, the better the chance of survival. A number of fungal organisms flourish at cold temperatures and attack the weak seedlings.

Seeds that germinate and emerge outside are well hardened off, but severe freezing temperatures can easily kill the young seedlings. If very cold temperatures are forecasted, the seedlings must be protected.

Transplants started indoors, properly hardened-off and later put into the garden are not as hardy as seeds started outside. Don't be in a rush to get your transplants out to the garden. These plants can easily be damaged by freezing temperatures.

Wood was an instructor with the Department of Horticulture Science. This column is provided as a service by the Extension Division and the Department of Horticulture Science, University of Saskatchewan.

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.