Causes of Long, Leggy Seedlings

Many who start their seeds indoors find that they end up with long, thin (“leggy”) seedlings. While this is mainly an aesthetic problem, it can lead to health issues for the plants later on once they’re planted into the soil. The taller the unprotected stem or stalk of the plant, the more heat loss and other problems it can encounter, affecting its overall health and productivity.

The causes of long, leggy seedlings are simple to take care of, however, and most experienced gardeners know how to do it. The stems are the result of rapid growth in the seedling, due mainly to problems with light and nutrient levels in the starting soil.

Causes and Remedies of Long, Leggy Seedlings

Lack of proper lighting or access to direct sunlight is the most common cause of leggy seedlings. Keeping them warm and in partially direct sunlight (meaning 2-4 hours of direct light daily and non-direct for 2-4 more hours) will keep your seedlings healthy. Sprouts tend to leaf more if they don’t have to climb towards the light. So having them elevated at the right height to receive light directly will prevent them from going leggy.

Using artificial light, such as grow lights, is another way to prevent legginess. Just make sure the light is about 8 inches to one foot (if a hot lamp, half that if not hot) above the plants (directly above) and they will stay low and grow thick and wide rather than tall and lanky.

Starting soil with too rich a nitrogen level can also cause seedlings to grow too quickly, becoming leggy. This is not a common problem, but some over-fertilize their starting soil and end up with plants that progress too quickly and become leggy and weak. Slow, steady growth is best for most plants.

Proper Calcium Levels for Starting Seeds

Another common problem is calcium depletion in the soil. Calcium is needed for cell wall structure in vegetables, so not having enough means weak plants that don’t grow well. Some plants are very sensitive to calcium levels and having too much can cause them to grow too quickly. This is relatively rare in vegetables, however.

The main problem is too much calcium is that it often comes at the expense of another vital nutrient such as phosphorous. That causes many problems in veggie plants. It also inhibits Vitamin B uptake into the plants.

Adjusting calcium levels can most easily be done through changes to the acidity of the soil itself. The higher the pH of the soil, the more calcium it will have available in it. If the pH is out of balance, calcium can bind with phosphorous which makes both the calcium and the phosphorous no longer available to the soil.

Too much salt (sodium) or other cations creates competition for the calcium, reducing the ability for plants to uptake this nutrient. This can be remedied with extra watering (to wash away the sodium) and through soil amendment with better composts.

Want to learn more seedlings?

Don’t miss these helpful resources:
Seed Starting Tips from University of Nebraska–Lincoln Extension
Starting Seeds Indoors from Purdue University Cooperative Extension Service