Fertilizing seedlings

How much fertilizer is needed by seedlings assuming they are in individual pots?

Is the fertilizer included in the normal watering shedule or should it be applied separately? If so how is it measured.

I am asking as I have seedlings in pots and cells from 1" to 4" depending on plant size and I think they need feeding but am concerned that I may do more harm than good.

Also what would be the smallest pot size that a plant could reach first bloom in. I am very restricted for room and my attempts to flower in the seedling trays were very dissapointing.

Any advice would be appreciated. Russ

I have been using Charlie Carp at half strength in my normal watering Russ. Seems to be doing the trick at the moment. Makes the greenhouse stink like fish though LOL

Hi Russ.

Those of my seedlings which have flowered ealy in the first season, have been mainly in pots 3.5"x3.5"x3.5" like these (you can see the one on the left throwing a flower bud):

As for fertilizing these potted seedlings, I first wait for the seedlings to develop at least a few sets of true leaves. I start soluble fertilizing them once weekly using Thrive Flower and Fruit (N/P/K: 15/4/26). The alternative high nitrogen Thrive is probably too high in nitrogen, and I have never used it. Both products are very similarly packaged, so I always double check I am reaching for the right one, off the shelf.

Pot size and fertilization depends a lot on the cross you’ve tried to grow. I very successfully get 144 seeds in a standard flat ~9 x 18 inch meant for 12 x 6 cell paks. With a mini, or something like Carefree Beauty x Circus I had essentially all that would bloom do so, under those conditions under fluorescent lights continuously on in a basement. They get Hoagland’s solution at roughly 3 & 6 weeks after the germinated seeds are transplanted to the flat.

The problem with common soluble fertilizers is that they use urea or ammonium salts which are not nearly so good as nitrates. But after the OK City bombing, natrates got a lot harder to find. You are totally dependent on having nitrifying bacteria in the soil. And they may not be present at high numbers in the soilless mixes. So there is a danger of leaf burn from the urea and ammonium accumulating in the plants.

But this year with OP Country Dancer, I’ve had essentially zero out of 1000 or so bloom. Perhaps the medium, but probably the parent. I did get blooms on some of the easier crosses, but I have very few remontant types going this year so I can’t say for sure.

If your weather is not too hot, you can get a 2nd round of bloom or go all summer in 2 " pots with floribundas and some shrubs, but maybe not with the really big HTs. Roots suffer stress at hi temps so going into the ground is preferred where I live with 100 degree days. Many years ago when I visited Nor-East, in MA, everything was growing in 2 " pots with drip irrigation. Minis will bloom like crazy that way.

Using cut-off half gallon milk jugs works really well for me to carry my special ones through the first summer. Pack them in close, on the ground and its nearly as good as being in ground. But come winter you can transfer to a frost-safe facility if needed.

This is a good question and there are probably many different answers, all of them mostly correct. Roses are a little like tomato seedlings in that they will start off great but really slow down, discolor, and are quite susceptible to sun burns and other types of insect and disease damage when starved. I lost almost all of my first yrs seedlings because I erred way on the under fertilize side of growing, among other things. If you want to use a rather safe, organic and mineral based, supports beneficial bacteria and microbe populations, and is slow release so it doesn’t overwhelm the seedling, I find Marine Cuisine by Foxfarm is really good. This is a low salt fertilizer, and salt build up with many conventional and petroleum based fertilizers can be a real problem when trying to keep a plant in a small pot. I use this on a lower dose than recommended but apply it 2-3 times before planting out. Some of my seedlings (not all) are right now 2-3 feet tall in 12 oz styrofoam coffee cups. I am planting them out as they go into their 2nd and 3rd blooms, but it is difficult keeping them watered on hot days. Some of them, esp. the ones that won’t bloom the first year are going into 2 gal pots, with many of the others going into the ground-right now my tomatoes are taking up way to much space, so I am creating a few new planters. Good luck, and it may surprise you how well 1 gal containers work for the first yr or two.

I use several fertilizers. If a seedling is not blooming after it has many leaves and is just sitting there, I use Miracle Gro Bloom Booster at about half strenth. This will usually get you some blooms if it is not a climber. Then after the first blooms I replant in bigger pots, what ever I have available, with about a cup or two of RoseTone mixed in with the potting mix which is usually Miracle Gro Organic Choice Potting Mix and/or the cheap Lowes, Walmart brand potting mix which I think is called Sta Green. I just dump bags of different potting mixes and the Rosetone into one big tub and grab the amount I need for repotting seedlings. This works good for me.

Hi Russ,

Roses, even seedling roses, love to eat. BUT, the smaller they are the more dilute should be the soluble fertilizer. You can drop it all the way down to 10% or less and get by with watering every other watering with the dilute fertilizer solution. I also do this with newly rooted cuttings and they really like it. Dilute is the key word.

Roses that are not thriving are very difficult to judge. Excellent roses look like trash when they are starved of nutrients and poorly watered (too much or too little). Culling under those conditions should be with trepidation.

Jim Sproul

Thank you all for your help. There is a lot of help in your posts.

There is one thing I am not clear on.

When watering with dilute liquid fertilizer do you simply apply with the normal water until it fills the pot or do you measure the actual ferilizer and water to each pot according to size and development of the plant in it (With my numbers at this time I can do this)

If measuring what would be a starting quantity for a 2" pot with a 2 leaf plant.

I know I am asking for details but this is because I have had a very poor year with my seedlings this year.

I planted my seeds in seed growing mix in 6" deep boxes this year intending to grow them in place untill I could cull them. I found it very hard to manage because of the slow germination.

I had plants that obviosly were in need of fertilization alongside fresh germinations that I was reluctant to touch, the growth was not good.

The result was my plants did very poorly so that in the end I potted everything up and put them inside under lights and started to fertilse with dilute liquid fertlilzer and fish and seaweed tonic.

Because this was done in desparation I used whatever pots where available so I put the smallest into 40 cell trays of 1.5"x 1.5" through 3" up to 4" pots for the largest.

Since then I have lost 1/2 the small plants and some of the middle range plants have have suddenly dropped leaves or died.

Some have finally stated to grow well and I expect the first blooms soon.

I want to get really strong growth from my seedlings so I can evaluate them early but avoid the risk of killing them with kindness as I dont have the nos or the space to experiment to find answers to my questions.


Hi Russ.

As far as what I do goes, I never feed with two or mor types of liquid fertilizer, however dilute. I would stick to only one type of fertlizer, whichever you prefer.

Also, whenever I do fertilize with soluble stuff, I just do it when it is time to next water the seedlings, and I just add as much volume of the stuff as if I were watering the pots normally, I don’t measure it more accurately than that.

Maybe you can prick out your more advanced seedlings out from the “communal pot”, one at a time, as they get a few leaves on them. That way you can fertilize your more advanced plants in their own pots, with stronger solutions, without affecting the less mature seedlings growing in the “communal pot”.

Also, I don’t fertilize newly transplanted seedlings, until they are obviously over the shock, and starting to grow new leaves in their new pots.

Russ, I usually mix up a gallon of water in a watering can and 1/10th TBS of soluble fertilizer (like miracle grow or any complete soluble fertilizer) for new seedlings. You have to have good drainage and it is best to keep the surface dry. You can do this by either watering from below, or by using a top dressing of perlite.

When I grew seedlings in trays under lights, I would use the 32 cell trays. The seedlings were always transplanted to these trays when they first sprouted in the communal seedling trays. I had tray liners underneath the trays and would always keep one of the cells open (unplanted, empty without any soil in it) so that it was easy to pour the dilute solution into the cell, making it easy to water from the bottom. After a few minutes, I would use a baster to suck up the rest of the solution from the cell (seedlings don’t like “wet feet” any more than larger roses). This worked well for me and I had very little seedling death.

Jim Sproul

Another trick that worked for me in the deep boxes was to put a layer of soil a bit further down with slow release fertiliser in it like osmocote for roses and then add a few inches of soil over the top sans fertiliser. As the seedllings grew they got their roots down into the fertilised soil whislt the seeds still to germinate had none. The Charlie Carp is not so hard on seedlings either and I’ve been watering my new seedlings with it every time I water.

After planting good healthy 5-7" seedlings and watching them shrink, disease and abort buds it was time for do or die action. Eight weeks of Miracle-Gro screw on bottles every 7 or 6 days at the recommended area coverage or less and in between one liquid application of pre-vintage 9/11 20-20-20 at the recommended rate, one pre loaded (worthless) garden feeder and one vaccination application of Bayer liquid 3 systemic products in 1. Watched the weeds and flower growth for over load and there was lots of rain for dilution. Only the climbers are 2-3ft. The others are par for 3years full growth, some with bigger than pencil size canes.

Big difference between last year and the year before for seed tray mix. Bad mold in all of the seed trays this year. Urban legend is dog and cat poo in the mix. Time to bring out the soil sterilizer and mix compost, dirt, ect. for this years seed trays.

Going to try delayed germination for better weather. conditions, maybe pea time or tomato time.

some of the middle range plants have have suddenly dropped leaves or died<<<<<<

Russell, what do you think has caused this sudden demise in those more advanced plants?


I am not sure what caused it but I am suspicious that it may be from fertilizer, that is why I asked the question.

These were plants that were not doing well before transplanting about 6 wks ago. When I decided to to remove them from the seed boxes they ranged from 1wk - 20wk old and 2 leaf - 6" plants that had flowered once. Many had lost leaves and dropped leaves in the boxes.

I added sand into the soil mix when transplanting because I felt that the seeding mix was “tight” and lacked drainage and I included garden soil and potting mix about equal parts in the hope that the problems would be solved.

I lost a few plants at transplanting (to be expected) but as they still showed little growth I started using 1/2 strength soluble fert. after 2 wks. Since then I have lost many as described earlier but also had the first sign of good growth and likely blooming.

This is why I asked for help. I want to avoid the same mistakes in future. I am sure that the plants need fertilizer early if I am going to evaluate them properly but want to avoid mistakes if possible.


Hmmm, I see.

That certainly sounds like lack of fertilizer. They may have been to weak to respond, or the roots may have atrophied by that point–and the ones that have responded were the stronger, not on their last legs, ones. It sounds so similar to what I did wrong-and what I was afraid of was over fertilizing them. I think I’ve got it now, and it is only the one to two week old seedlings that are easily susceptible to really over fertilizing. This is where the less than 1/2 strength solution of a Miracle Gro type fertilizer, once a week gets them off to a good start.

Hi Russell,

You could have had spider mites. Before I tranfer my germinated seedlings into any soil, I usually wet it down good and let it sit outside for a few days in a container that has holes at the bottom such as a big pot, sometimes I will throw bags of ice on it and let that melt through, and you could pour some boiling water through it. It is especially good if it is going to rain and/or snow to leave it out so it can really get soaked. But make sure when you are ready to use it that all excess water is taken out and your potting mix is moist but not too wet. I will take handfuls at a time and squeeze the water out till there is no more water coming out of it and it is still wet, but not soaked.

I use 16 oz plastic drinking cups to start with and then transfer them later as they grow. They are cheap. I never water my seedlings because I keep them in a clear plastic tubberware tub with the lid on under the lights. There is enough moisture that builds up in there that they stay very moist and they need no water.

By November or Dec. my seeds are all planted in moisten play sand in small plastic baby food containers and kept in the regrigerator until they germinate or around 3-4 months take the containers out and leave them at temperatures of 55-65 degrees for 1 week and then back in regrigerator. I repeat this every so often. By April they come out for about a month, I sometimes plant the seeds in soil to see if they will take off after that. If they do not germinate by the end of May they go back in frig till next year.

There is no specific way of doing this, everyone has their own little system and as you go along each year you develop your own according to your surroundings and environment. You will find out what works for you after many trial and errors but just don’t give up.

I just want to say also that I do not keep the seedlings in the tubberware containers long, only until they grow strong enough to take outside with weather permitting. I then transfer them into bigger pots if they need to be and keep them in a all day shaded area, then move them to partial sun, then to full sun. Never take your seedlings outside from inside and put them in full sun, they will definitely burn to a crisp. Do it gradually.

How soon can very dilute fertilizer be applied to germinated seedlings?

I am only going to use NPK soluble powder fertilizers, so I would love any answers on these types of fertilizers.

I plan on starting with a very dilute solution (eg. 10% x full strength) to start with, like Jim has commented on, earlier on in this discussion.