Garden Talk: How to Fertilize Your Homegrown Seedlings

Hopefully a few weeks ago you got started with some of your favorite potted vegetables and flowers. Now is the time to start fertilizing those plants.

Tomato, pepper, broccoli and other vegetable seedlings need food for rapid growth. The food is in the form of liquid fertilizer.

Brendan Rennie is the greenhouse manager at Bordine’s in Brighton, MI. Rennie says we don’t want to start fertilizing small plants too early. He says for him to wait until the seedlings are three inches tall, which should be now or very soon for his seedlings. Rennie says to use a liquid fertilizer and not make it too strong. Small plants can get burned early with too much fertilizer. The burn would look like brown or yellow leaf tips.


Liquid fertilizer recommended for seedlings. (photo provided by Bordine’s)

It says to find a balanced fertilizer, which means that the three numbers in a fertilizer analysis would be about the same. The fertilizer numbers on the box might look like 20-20-20 or 10-10-10 or 5-5-5. 20-20-20 is a strong fertilizer with 20 percent nitrogen, phosphorus and potassium. 20-20-20 fertilizer should be used at half strength for new seedlings. Read the fertilizer box for instructions on how much fertilizer to mix into the water. Many fertilizers are made to put one tablespoon of fertilizer in one gallon of water. This would be too strong for seedlings according to Rennie. We should use only half the amount of fertilizer in the gallon of water. 10-10-10 or some similar analysis is a good fertilizer.

Rennie also says that many people like an organic fertilizer called fish emulsion. Yes, it’s what it sounds like: ground fish. The analysis of fish emulsion fertilizer is 5-2-3 and it is not too strong to water seedlings.


Seedling fertilizer (photo provided by Bordine’s)

Fish emulsion fertilizer doesn’t smell very good. It makes a good fertilizer, but you’ll also find that your cats and dogs may suddenly want to help you garden.

Byron Brideman, lead grower of From Buds To Blooms in Essexville, MI, has a slightly more detailed fertilizer program developed for Michigan’s dark skies. Byron says that the darkness and cloudiness of March force him to fertilize the seedlings using or without a lower average number. His preferred ratio for the first few fertilizer applications is 15-0-15 or 15-5-15. Brideman says the middle number, phosphorus, will cause seedlings to overstretch and become limp during February and March clouds.

Brideman starts fertilizing the seedlings a little earlier compared to Rennie, but also says to be very careful at first. For Brideman, once the seedlings have two true leaves, he applies the fertilizer at a quarter of the recommended rate. He does that low rate three times and then uses clear water on the fourth watering. He then he increases the strength of the fertilizer in half for three more fertilizations. After another clear watering without fertilizer, he goes to full rate.

Brideman then uses a balanced fertilizer with equal numbers once we get to the sunniest part of April and May.

Both growers say we can use the same fertilizer on all of our seedlings, whether it’s a tomato, pepper, cabbage or flower crop.

Start feeding your seedlings now so they’ll be big and healthy when it’s time to plant them in your garden.