Colorado plant expert answers your seed-starting questions
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LONGMONT, Colo. — Starting plants from seeds can save gardeners money and give them a head start when summer arrives, but the process can be fickle.
Across the Front Range, the last spring frost typically falls around the first week of May. Gardeners should consider starting seeds indoors four to eight weeks before the last frost date in their area.
Rocky Mountain PBS spoke with Tommy Roth, a horticulture specialist with the Colorado State University Extension to answer common seed-starting questions.
This conversation has been edited for length and clarity.
This conversation has been edited for length and clarity.
Video: Cormac McCrimmon, Rocky Mountain PBS
Rocky Mountain PBS: What plants are easiest for beginner gardeners? What plants should they leave to the pros?
Tommy Roth: The growing conditions here are not ideal, right? It's really, really dry. Our soil is so bad, but that shouldn't discourage anybody because there are lots of things that you can grow. I would say if someone wants to start out, pick a tomato or a pepper.
And if you're going to pick a tomato, make sure to pick a cherry tomato. Cherry tomatoes do a lot better than large tomatoes in Colorado. The large tomatoes, they dry out, but a cherry tomato that doesn't happen with.
Plants that should be left to the pros, I will say the big one is broccoli. Broccoli is produced generally in very humid climates, especially climates where there is a lot of fog in the morning. What you're actually eating in the broccoli is flower buds. It's unopened flowers. To get them tight and bunched like that, it has to be humid. And in Colorado, it's not; it's super dry.
They're not going to get bunched like that. They're not going to look like how you think broccoli should look like. They're to get spindly. They're going to get leggy. One hundred percent avoid broccoli. I would buy that at the store. It's really hard to do here.
TR: Seeds don't have a 100 percent chance of germinating, so I would say probably put two or three in each seed container to make sure that there's going to be a seed coming out.
They're not going to get bunched like that. They're not going to look like how you think broccoli should look like. They're to get spindly. They're going to get leggy. One hundred percent avoid broccoli. I would buy that at the store. It's really hard to do here.
RMPBS: Is it best to put one seed per container or make it rain?
TR: Seeds don't have a 100 percent chance of germinating, so I would say probably put two or three in each seed container to make sure that there's going to be a seed coming out.
And then we do something called thinning. Say you plant three seeds in a container, all three germinated and one of them is looking a lot stronger and growing a lot faster than the other two. You're going to want to cut back the other two and let the strong one survive. It's survival of the fittest with the plants. We want to grow the best ones.
RMPBS: My apartment doesn't get much natural light. How can I ensure my seeds have enough light to survive?
TR: This is really hitting close to home for me. I live in an apartment that is northeast-facing, which is literally the worst direction to be facing for light. All my houseplants are sad. I'm not able to start my seeds, just from natural light. I'm going to have to buy a supplemental light source. You can get these at Home Depot, at Lowe's, any garden store, they'll sell supplemental lighting. And you'll want to hang this from a rack or something so that it can be above the plants.
Usually, I like to do about 12 inches above the surface of the soil. And then as the plant grows, I like to lift it up more and more.
Usually, I like to do about 12 inches above the surface of the soil. And then as the plant grows, I like to lift it up more and more.
RMPBS: When should I start seeds indoors?
TR: You’re generally going to want to start seeds indoors about four to eight weeks before the last, killing frost. On average, our last frost is on May 6 in Boulder County. If you're in a different part of Colorado, consult the internet.
You'll be able to figure it out very easily. And you're going to want to count back four to eight weeks from that point to start them. If you start them any earlier, the plants are going to start getting too big. They're going to outgrow your set up.
If you start them too late, they're not going to be old enough to survive the harsh, windy, hot, dry conditions that you could find in the middle of May.
RMPBS: When should I move the seedlings outdoors?
TR: Right after that last killing frost. Now, I will say, if you move them outside on May 7 — that May 6 number is an average. I am not going to guarantee you it's not going to freeze. So, you know, use your best judgment. A really safe date would be Mother’s Day is what we usually tell people. It generally almost never freezes after Mother's Day. But if you're really rearing to go, May 6.
One thing that you'll want to do before moving them outside is something called hardening off. Hardening off is a process where you will bring out your seedlings for an hour, and you want to expose them to the UV radiation that the sun is going to be putting off. So plants, just like humans are, can get a sunburn. They can get burned by UV radiation. Maybe your first time, you'll do it for an hour, maybe the second day, a couple hours.
And you want to do this for two weeks. And then once they're hardened off, they're ready to be put in the soil and they won't get a sunburn. Then you'll be having healthy plants.
RMPBS: How should I water seedlings?
TR: You're going to want to use a watering device that diffuses the water. So you don't want to be pouring a really fast and hard stream on your seedlings, because would you feed a baby by putting them under a sink faucet? Probably not. That would really traumatize the baby. And it's kind of the same thing with plant seedlings.
RMPBS: Which plants are better sown directly in my garden?
TR: So I would say in Colorado we have a very short growing season here. It's four to five months depending on the weather. And because of that, if you want to grow something that takes more than four to five months to fruit, it's probably going to be a good idea to start that indoors.
Things that are better directly sown are usually things that are vegetables. So things like that, you eat the leaves off essentially. So herbs, kale, lettuce, things like that. They don't they don't generally like to be transplanted. So oftentimes it's better to just directly sow those into the soil.
RMPBS: What else should I be doing this time of year to prepare my garden for the growing season?
TR: I would say this time of year, it's a good time to start amending the soil. Our soils here are very salty, and they're very rich in all nutrients except for nitrogen. Nitrogen is a fast-moving nutrient. It needs to be reapplied every single year.
RMPBS: What separates professional growers from household gardeners when it comes to germination?
TR: It's a great question. I would say a lot of money and a lot of facilities. When professional growers grow, they're growing an entire greenhouse of the same thing. So, they can really make the conditions in that specific greenhouse completely perfect for what that plant is.
RMPBS: What's your top piece of advice you have for anyone starting seeds?
TR: I would say, don't get sad if you fail. I've failed so many times starting seeds. Oftentimes, if this is your first time, starting a seed, you might not get it right. That's totally fine. This is something that you learn over years.
To give yourself a better chance of succeeding. Look at CSU Extension’s free fact sheets online. We have tons of resources so that you can make sure you're doing the best practices and have the lowest chance of failure.
Type of story: Q&A
An interview to provide a single perspective, edited for clarity and obvious falsehoods.
An interview to provide a single perspective, edited for clarity and obvious falsehoods.
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