Question
QUESTION: Hi,

which NPK should we use for Kalanchoe and Rose ? I read one article told NPK 2:1:2 good for blooming Kalanchoe flowers, another article said NPK 1:3:1 is better. I'm confused now. Ditto for roses, which NPK good for blooming flowers ? Can I add CaO (from drying material like silica gel) and Mg(OH)2 (from medicine for stomachache) ? Thank's for your help.

Rgds,

Ari

ANSWER: These amendments are moot, my friend, because you do not know what you HAVE in your Soil.

You have one container of 2-1-2.  Another with 1-3-1.  You think you are putting it in current 0-0-0 Soil?  Think again.  There's microbes in that Soil  Are you dealing with Soil in the garden, or Soil in a pot?  Makes a big difference.  Who knows if you need ANY Mg or Ca at all?  There's only one way to find out.

Give me your zipcode, and I will give you all the information you need to TEST YOUR SOIL!



---------- FOLLOW-UP ----------

QUESTION: Thank's for the reply.
I'm dealing with pot soil and actually I don't want to bother so much with testing soil.

Let's say that we have 0-0-0 pot soil, which NPK is best to bloom Calandiva flowers ? 2-1-2 or 1-3-1 ? Ditto for Roses ?

I read once that Phosphate helps to bloom flowers and Roses need lots of Nitrogen. Thank's.

ANSWER: You're right to assume that potting Soil is a very different environment from outside real estate landscape Soil -- the kind that we submit for testing.

So let's go over the rules about fertilizing potted plants.

IF you have a plant that is growing in a big enough pot (very hard to do with Roses), IF you have a plant that is getting enough Sun (ditto), IF you have a plant that has not been over-fertilized, there MIGHT be a need for Phosphorus.

Roses however need a lot of Nitrogen because they don't build flowers out of Phosphorus.  They build flowers out of energy from photosynthesis, which is completely determined by the NUMBER OF LEAVES they have.  Every Rose is different, but if you spike a Rose's diet with Phosphorus, there will be at BEST no effect, and at WORST a shortage of other nutrients; the Phosphorus is something of a bully and it takes up all the space that other nutrients need when you put down too much.

Kalanchoes are succulents.  They have a lot of leaves when compared to Roses, they need a LOT less light, they are simpler plants and grow very well as pot plants.

The most important rule you can follow for both of these -- both are potted plants -- is that you NOT use chemical fertilizers OR potting soil that comes with fertilizer mixed in...

because...

The chemical fertilizers build up as 'Salt' and damage the plants after a season of this.  The soil is Salty, the plant is miserable, becomes susceptible to disease, you don't know what's wrong and then all h$@^ breaks loose.  Stick with Bone Meal for Phosphorus, which releases very slowly (via microbes), and Fish Emulsion or other gentle Nitrogen fertilizer for your Rose.

I understand why you would want to get a simple answer about the N-P-K.  Fertilizer companies like to push this idea.  It's all marketing.

In the outdoor world, where soil testing IS done, Phosphorus builds up in the soil until nothing blooms.  Then we test, and we find out what's wrong, and stop pushing P.  Most soil is fine and dandy for growing anything you want, with no fertilizer.  Organic matter is the best amendment you can give it.  That goes for potting soil, too -- Compost, composted Manure, composted Humus.  They are not N,P, or K, but they build strong bodies 12 ways.

Your Calandiva is a state of the art Kalanchoe.  This will turn heads once it's up and running.  Just don't give it too much light, and after a rash of flowers, deadhead and let it rest a month and even dry out to recover.

If you can grow a Rose in a pot long term, you should go into botany for a living.  Watch out for Spider Mites and Aphids.  Good luck.  Any followups, I'm happy to read them.

L.I.G.

---------- FOLLOW-UP ----------

QUESTION: Hi L.I.G,

if you suggested not to use chemical fertilizer for potted plants, then how about using SLOW released chemical fertilizer or chemical fertilizer dilluted in LARGE amount of water (1 teaspoon per 1 ltr ?) every two weeks and after 1-2 years (or perhaps shorter ?) change the pot soil with new one without any fertilizer mixed in and start using those mentioned fertilizers again. Is it a good idea ? What do you think ?

I'm saying this because I have difficulties to find or store Bone Meal and/or Fish Emulsion. More cleaner and easier for me to keep chemical fertilizer in a bottle.

Rgds,

Ari

Answer
Slow release is better than fast release - so yes, you have the Long Island Gardener seal of approval for this activity...

but...

ONLY if you need it.

The trouble with Soil in a pot is that it does become depleted.  Some people go to the (extreme) measure of re-placing all the Soil in the pot when they re-pot.  This is terribly stressful for the plant, not to mention the potting engineer him/herself.  But it does take years to reach that point where you are cultivating plants in 'salty' Soil and notice any symptoms.  Odds are you will be battling many other problems before you reach that point.

Given that these are fairly new plants with new potting Soil, I would expect there is no need to feed your plants just yet.  But I am a small solitary voice in the scheme of things, out-volumed by multinational fertilizer corporations with mega-million ad campaigns.  They're only too glad to sell you anything you want to buy, whether you need it or not.  I suspect you have a great deal of experience growing certain plants, probably with quite a bit of success.  And I also expect you will be successful with these too -- it was probably no accident that you picked the state-of-the-art when you chose to grow the Kalanchoe you did, and a comfort level with Roses are nothing to (pardon the expression) sniff at.  The old sage gardener's saying comes to mind here: If it isn't broke, don't fix it.  So if you are having success with fertilizing, even in situations where I would not advise it, then you should continue to do that.  It works, right?  Can't argue with success.

If someone with less competence however comes along and wants to know how to fertilize these, I would point out the potential for salt buildup (which is always there), and advise them to cut back on chemical fertilizers.  It is quite realistically much easier to use them -- organic fertilizer takes up a lot of space, and if you are nto used to using them, they are a bit of an inconvenience.  That can take a lot of the fun out of potted plant culture.

However, consider this: A self-fertilizing potted plant does not need to be fertilized because it is on the self-service line at the food store.  Microbes in the Soil are like little food factories, generating a lot of different elements.  That's a convenience you should at least file, and then revisit later, when it makes sense to you.  Not when it makes sense to me.

Good luck with these, and keep me posted.  Summer's coming and who knows what lies ahead?

L.I.G.