poor root development

I have been starting seeds under grow lights for many years. I also have a greenhouse to which I move the seedlings in late March. I have tried many techniques but my seedlings always have small roots, even in mid summer. I do not overfertilize. Any thoughts? I am wondering if my water may not be right or it may not have the right ph. hmmm... I can't figure it out.

Hello mdeano,

What plants are you starting?

Is the size of the roots proportional to the plant? Small seedlings aren't going to have a ton of roots, the roots will grow as the plant does. If the whole plant is smaller than you think it ought to be, then maybe you're not fertilizing enough. If it's just the roots, then you might try a product like SuperThrive or some sort of root booster, that may help.

Another possibility might be your pot size--with my seeds, I start them off in cell packs, then move them into 2" pots, then 4", etc. I've noticed that when they're still in the cell pack, they grow to a certain point but then don't really get much bigger until I pot them up into the 2" pot, then same thing, they grow to a point but then don't grow much more until I move them up to the 4" pot. You don't want to overpot them, but you might try potting up right away as soon as they're a size that's close to appropriate for the next pot size up.

Are you watering from bottom? Doing so can make the roots reach deeper for the water in my experience.

Thank you all for your information. I plant all kind of seeds - mostly flowers. I have used Super Thrive, Messenger, fish emulsion. I water from the bottom. I start is cell packs and move to 3# pots. Last year my delphiniums were about 3 inches tall and the roots were about 1 inch. I didn't plant them in the spring because they were not big enough. I waited until late summer. We had a severe drought in the summer so I did not want to plant during that time. I'll see if any of the 25 seedlings survived. Maybe I don't switch to a bigger pot soon enough. Any other suggestions for a root booster? Root Shield? I have not tried Maxicrop (hard to find). Thanks again for your input. You can see why I am frustrated.

Once you're safely past your last frost date, you can plant the seedlings outside even if they're small (may want to put a little wire fence around them to protect from rabbits munching them or people/pets stepping on them). A lot of times they'll grow and develop faster in the garden than they were in your pots. Just make sure you harden them off properly and get them used to the sunshine first. But I think they should be growing faster even if they're in pots, my thought is either you're not fertilizing them enough, or you need to pot them up sooner.

the best way to get good roots is to keep the soil as dry as possible. Water only in the am and let the soil dry out before evening. Water only when the soil is dry, but don't let the soil get bone dry with seedlings-but you can get let them get pretty dry. You would be surprised how well seedlings handle soil on the dryer side.

Roots need oxygen to grow, and water displaces oxygen, so thats why you want dryer soil. Roots grow at night, and thats why you water in the am and let the water drain out before evening.

Interesting thread, tigerlily has a point.

Great tips from everyone! I will let them dry out more consistently. I have always tried to keep the young seedlings moist... hmmm, an old dog can learn... and learn and learn! I absolutely love growing from seeds! I order way too many seeds every year.... this year I will try to use the old ones (presoak in hydrogen peroxide etc). I get bored planting all of the plants so I end up giving away half and throwing away the rest... too sad. When i give them away, many friends don't plant them and off they go to plant heaven! My friends want BIG plants.. not the teeny, weeny ones I offer them... they do look healthy but not like the big pot perennials! oh well.. I just love those seeds!

When growing seedlings, you need to use a plant food that is high in phosphorus. You have 3 numbers on all plant food. Nitrogen, phosphorus, and psotassium. The higher the phosphorus, the more root development. I use a fertilizer with 30% phosphorous. using a soiless growing medium is also importan for root development. Knowing the lenght of day for each plant that you are growing is also important. Make sure that you are using a spray bottle with warm water. Using these steps should increase your luck with your plants.

"Stay Happy and Keep Gardening!"

Ironsides, I think its potassium, the third number that is more for roots and the general well being of the plant and phosphorus is more for blooms. Most plants, including annuals that bloom/will bloom do not need high amts of phosphorus-they can't utilize it.
I am not sure when you use the spray bottle, but I think its usually best to try to keep the foliage dry unless you are watering the plant/soil.

WRONG!.Phosphorus comes from phosphate, which everyone including plants need to grow. Phosphrus devlopes root growth. I have been gardening for over 40 years, and know which each number stands for in fertilizer. Until you understand what a plants needs to grow, you will have problems.

I agree w/ Ironsides.

Phosphorus also helps with blooms...that's why all the bloom booster fertilizers have a high middle number. For blooms you also need to make sure not to have too much nitrogen, but phosphorus helps too (with most plants at least...things in Proteaceae for example don't like phosphorus at all and if you give them too much of it they'll die)

Ironsides, I am not saying that plants, and in particular annuals-which i am, perhaps wrongly, assuming that we are discussing here do not need any phosphorus at all. I am saying that they do not need high amts of it-that they cannot use it all if you give it to them.

Here are the numbers on the different liquid/foliar fertilizers that I use to on my annuals from when they are seedlings to when they are ready to be planted:
20-10-20, 13-2-13. 15-0-15. 21-7-7. You can see that the phosphate number is always the lowest number.

tigerlily123,

The numbers you are using are too low in phospherus. I use 20-30--10. You see the middle number is higher. That is for root developement. Once they are on their way, I use a different fertilizer. You don't want higher number in nitrogen in growing seedlings. That is the same principal when growing grass. Too high of Nitrogen will cause fast leaf growth, but low root growth. That is because of the low number in phosperus. I am not telling you what to use, I am just saying that is the reason mdeano is having problems with low root growth. I did not establish this policy. Scientist and many agricultural people have found this out many years ago. All farmers and gardners follow thsi principal. And every plant, does not matter if it is an annual or perinal, or grass. If the phosphorus level is too low, you will have poor plants when they are devloping. Once they develope, you can change fertilizers, but the numbers you are using are still wrong once they are developed.

"Stay Happy and Keep Gardening!"

Ironsides-thanks for your reply. I guess that I should say that i grow annuals for a living-I am a commercial wholesale bedding plant grower and have been doing it for almost 20 years. In the trade, it is a well known fact that annuals, and alot of other plants do not/cannot utilize as much phosphorus as you are advocating. But if it works for you then that is great!

WOW Lots of information here. What are the brands of fertilizers that you use? Maxicrop? Fish based? I guess for both the Phosphorus opinion and potassium opinium. I don't know which is correct but it appears both sides have been successful. Thanks again! I am going to buy my seeds today.

I just potted up some pansies I had started about 3 weeks ago. I kept them rather dry . . .OMG you would think they were trying to send roots to China!

Honestly, these little guys were just starting to get their second set of true leaves - in other words they were still "babies" but some of the roots were 3 times as long and more full than the tops of these little guys. (some roots were almost 3 inches long!)

They were started on heat mats with lights, and then after about 10 days taken off the heat mat and received just light. Alas - I didn't set them up to be watered from the bottom, so I had to water from the top. I honestly believe it was because they were on the dry side, just as tiger stated earlier in this thread.

Anyway, in future I will water from the bottom :-)

This is the first year I've used lights and stuff. I've always just planted seeds in early spring.
I'm glad you posted this thread, cause I'm having trouble with kind of same thing. I have some under lights that I've used the jiffy pots with and some I used the pellets.
As they are growing, I pick them up to look at them, and a lot of times there are these liitle string roots coming out. I'm scared to repot them because the roots are so fine.
I leave myself in allof your capable hands.
Ya'll were talking about fertizizer. When I transplant the seedlings I've been puting them in the miracle grow that has fert. in it. Is that ok and is it enough