Growing plants from seed is a fun challenge that allows you to save a little money on gardening supplies and gives you a much wider range of options in terms of what to grow.
However, seedlings can be finicky and sensitive to less-than-optimal environmental conditions. Growing seedlings for the first time can be frustrating, especially if the plants are failing to thrive for reasons you can’t ascertain.
If your seedlings don’t look quite like the ones at the nursery, there are a few key issues that may be to blame.
Melissa Higgins at Sprague’s Nursery said that a lot of the problems with seedlings can be boiled down to “killing with kindness,” or using too much water and fertilizer.
“I feel like everyone just keeps everything soaked all the time thinking they’re doing everything a favor when in fact it’s kind of almost the opposite with seedlings,” Higgins said. “You can do a lot of damage keeping things wet for too long, way more so than if they were dry.”
Paradoxically, overwatered plants may look like they are drying out, with yellowed, drooping or curling leaves.
“They will look like they’re drying out and we just kept watering and watering,” Higgins said. “Probably what was happening was the root system was starting to rot and the foliage was starting to wilt and look bad.”
Higgins said that another sign of overwatering to look out for is fungus gnats.
“Everyone wants to call them fruit flies, but they’re eating the mold from the soil because it’s too wet,” she said.
Yellowing and spotting on leaves coupled with stretched-out stems, or “legginess,” can also be an indication that you have over-fertilized your seedlings.
“[Look out for] spotting of the leaves, any yellowing on the edges of the leaves,” Higgins said. “Too much fertilizer can cause burning and it can also cause stretchy-looking plants that are too tall and spindly. Fertilizer is going to cause plants to want to grow faster.”
Kate Garland, horticultural specialist at the University of Maine Cooperative Extension, said that she commonly grows seedlings without using supplemental fertilizer. If your seedlings are struggling, she said not to jump to fertilizing as a solution, as it may exacerbate the problem.
“For those that are seeing not perfectly green leaves, don’t just jump on the fertilizer bandwagon thinking that will solve your problem,” Garland said. “Most of the time it has to do with the environmental conditions: too cold, or too hot, or too much water.”
Lack of light
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If seedlings are stretched out or leggy they also might not be getting enough light.
“Inside without as much light as they really need, they’re going to stretch,” Higgins said. “They’re going to be growing too tall and spindly.”
Low light will also cause other problems, such as light-colored plants with see-through, papery foliage.
When it comes to starting seedlings indoors, Higgins said that having too much light is never really an issue, though cold season crops will want out of the heat and sun once they mature.
“There’s not really too much light on anything,” Higgins said. “Our plants get full light all day long in a greenhouse, and that’s not an issue.”
Cold conditions, especially coupled with other environmental challenges like overwatering, will result in purpling stems, black spots and stunted growth.
“They’ll stay wet a lot longer because the soil is not drying out,” Higgins said. “They probably won’t continue to grow if the soil is too cold. They’ll just sit.”
Black spots, Garland added, can also be a sign of a fungal pathogen. When it comes to discoloration in seedlings, asking your local cooperative extension agent will best help to diagnose the problem.
“Whenever concerns related to spots on a leaf or discoloration on leaves, they can send us pictures,” Garland said. “It’s not something we can easily diagnose through a description. We can find out by looking at a picture in an email.”
Investing in heat mats for seedlings, especially warm season crops like tomatoes and peppers, will help with issues for cold indoor climates, However, cold conditions can also be an issue once you transplant seedlings into your garden.
“They just kind of sit until the temperature warms up, until the soil warms up, then they’ll grow,” Higgins said. “Sitting there waiting is just an indication that they’re just too cold.”
Garland added that abundance of heat isn’t usually an issue for seedlings in indoor settings.
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“Sometimes people have their heat lamps on too high or for too long and you get some stunting growth,” Garland said. “Foliage [that’s] a little more reddish in appearance is a sign of stress. Again, that depends on the crop.”
However, it can become an issue when you transplant your seedlings or grow them outdoors in a greenhouse or cold frame that isn’t properly ventilated.
“People are often surprised in April and early May how quickly those little microclimates you’re creating can heat up,” Garland said. “People fry their plants in their settings.”
To toss or tend to stressed seedlings?
Before you transplant, you have to decide whether or not your seedlings are damaged beyond repair. Garland said that if discoloration in seedlings — yellowing leaves, purpling stems and the like — happens rapidly, then it might be best to start over.
“I encourage folks to not wait too long,” Garland said. “Your seedlings can look ok, but they’ll limp along and they may not recover fully. If it happens overnight and you see things just yellowing or purpling pretty quickly, I suggest just culling them out and replacing them.”
However, Garland noted that some plants — such as certain varieties of tomatoes — have naturally purple stems and foliage. Knowing your plant will help you determine whether the seedling is developing normally.
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Sometimes, seedlings are salvageable even if they present tell-tale signs of stress.
“[Cold seedlings] could be salvageable as long as you give them some heat,” Higgins said. “If they look like they’re going to come back and make some new leaves, keep them. If not, chuck them. It’s not worth spending the time to plant it outside if it’s really just not going to produce.”
When it comes to legginess, Higgins said to cut your losses if the seedlings can’t stand up on their own.
“They shouldn’t need their own support,” Higgins said. “You shouldn’t have to use a popsicle stick to get them to stand up straight if they have enough light. If you’re looking at it and it really just looks poor quality, like it’s not going to sustain itself outside, then you might as well chuck it.”