Why are my cacti not flowering?

[DaveW]

"You need something that has more potash and phosphate than nitrogen."

As Greenknight says above, too much nitrogen can lead to rampant growth rather than flowers. Try half strength Tomato fertiliser occasionally since that is compounded to encourage flowering and fruiting rather than excessive plant growth.

[chancey84]

I didn't realize that cacti do better with less nitrogen. When I was looking online last yr for the best fertilizer for cacti I came across an article on ammonium nitrogen and acidic water. It sounded like great information and that the plants and cacti did really well. It called for a 20/20/20 fertilizer that consisted of urea as the form of nitrogen and it usually is washed out or breaks down. So the ammonium sulfate is added to balance the mix. Moving forward what fertilizer do you recommend or best NPK percentage to look for?

[DaveW]

A friend of mine who was a nurseryman used to give higher nitrogen fertiliser when the cacti were actively growing, but changed to lower nitrogen ones when they were starting to flower and fruit, and towards the end of the year to harden off the new growth when approaching winter.

People swear by different fertiliser combinations, I suppose it depends on what your potting mix actually lacks regarding nutrients. Plants grown in purely mineral mixes may need a different set of nutrients to those in soil based mixes where the soil itself provides most of them. In hydroponics on inert substrates all nutrients and trace elements must be provided since they get none from the soil as in conventional potting mixes.

This link gives the N.P.K composition of various fertilisers. You will note those compounded specially for cacti usually are lower in nitrogen than general fertilisers designed for normal leafy plants. I suppose the danger with high nitrogen fertilisers if cacti don't take up much nitrogen is the toxic build up of salts in the potting mix, but that can be countered by periodically leaching the pot.

http://succulent-plant.com/fertiliser.html" onclick="window.open(this.href);return false;

[chancey84]

Thanks for the help. I appreciate the link. I'm gonna make some adjustments!

[7george]

Also, in another thread you mentioned using 20-20-20 fertilizer. Cacti don't need much nitrogen, using too much nitrogen encourages more soft vegetative growth and less blooming. You need something that has more potash and phosphate than nitrogen.

I agree with this too.

[chancey84]

Yes. Last yr I fed a teaspoon of a 20/20/20 water soluble per 5 gal. Each watering and used rainwater with a lowered ph around 5.5. Is there a specific fertilizer that you would recommend? And would you continue to keep the ph down or straight rainwater?

[chancey84]

Is there a certain fertilizer that you would recommend?

[greenknight]

Not really, something that's higher in phosphate in particular helps encourage flowering - and continue using a weak dilution. Straight rainwater is fine, you need to adjust the ph only if you're using hard water.

I've been using African Violet fertilizer since the African Violets got cyclamen mites and died (quite a few years ago). You use much less fertilizer for cacti, so one bottle has lasted for years.

[DaveW]

Over fertilisation can promote growth at the expense of flowers. Plants grown hard tend to flower more than rampant growing over fertilised ones.

http://homeguides.sfgate.com/overfertil ... 45795.html" onclick="window.open(this.href);return false;

http://www.cactusinfo.net/fertilize.htm" onclick="window.open(this.href);return false;

[chancey84]

Thanks for the info. I really appreciate all the help!

[greenknight]

I just checked, the stuff I'm using is 6-9-5, and I usually apply it just once a year - unless you use a pure mineral mix, you don't need to supply fertilizer continuously. I also add a little bit of wood ashes to my potting mix - not very much, since it raises the Ph. That supplies a bit more potash, a tiny bit of phosphate, and trace minerals.

[DaveW]

Even with so called mineral mixes I suspect some nutrients are present, baked clay for instance, since clay is after all a major constituent of soils and has only been baked therefore will still contain some soil minerals:-

"Clay soils are heavy but high in nutrients."

Also pumice is lava rock and volcanic soils are some of the most fertile in the world. Only with hydroponics using some perfectly inert substrate will no nutrients be available from the mix, therefore requiring any fertiliser to supply them all.

http://www.lava.gr/en/products/holyston ... ttributes/" onclick="window.open(this.href);return false;

From the Bonsai site link below:-

"(Pumice) With a cec that hovers around 75 meq/100g (depending on source) it requires less frequent fertilizing that most other soil components when used alone. Pumice can hold large quantities of water - up to four times its own weight. This, coupled with the soft and easily powdered surface means that when used alone or with other absorbent materials, careful watering is necessary to avoid water logging."

"Pumice drains well but tends to drain less well after a couple of years in use. However, drainage is never impeded to the extent that it becomes a problem."

"Turface has a moderately high cec of 33 - 35 meq/100g and can absorb vast amounts of water. Pour water onto dry surface and you can hear it soaking and see steam arise as it does so! This incredibly high absorbency can be both a blessing and a nightmare, depending on the quantity used. although when used undiluted it seems to be a good medium for newly dug trees, as soon as the inter-particle spaces are full of roots, it readily becomes waterlogged. When sold as a soil amendment (its original purpose) the manufacturers of Turface recommend a rate of no more than 15% by volume, and I would suggest that rate should also apply to use in bonsai soils.

Some suggest that after a while the moderately high cec can cause Turface to adsorb concentrations of nutrients so high that it can cause reverse osmosis resulting in "root burn". In theory this is possible, but you would have to be consistently feeding very heavily for some time for this to happen.

Turface substitutes such as oil dry and kitty litter are less stable and not really suitable as a soil ingredient."

http://www.colinlewisbonsai.com/Reading/soils2.html" onclick="window.open(this.href);return false;

However Kitty Litter seems to work OK for cacti.

[7george]

http://postimg.org/image/nih5hro0p/" onclick="window.open(this.href);return false;
http://postimg.org/image/nih5hro0p/full/" onclick="window.open(this.href);return false;

This thing is better then 20_20_20 solution.

[DaveW]

Similar ones are available in the UK:-

http://www.vitax.co.uk/home-garden/vitax-cacti-feed/" onclick="window.open(this.href);return false;

http://www.vitax.co.uk//wp-content/uplo ... i-Feed.pdf" onclick="window.open(this.href);return false;

http://www.marshalls-seeds.co.uk/westla ... lsrc=aw.ds" onclick="window.open(this.href);return false;

Also Chempak:-

"Chempak – Cactus & Succulent Fertilizer
A water soluble, high phosphate feed ideal for cactus and succulents growing in small containers. Useful for plants grown indoors in artificial light conditions. NPK 8.34.32 + trace elements."

I suppose the question really is do cacti take up excess nitrogen in fertilisers and hence make lush soft green growth, or do they only take up the small amount they need, therefore leaving a build up of excess nitrogen in the pot from high nitrogen fertilisers that can become toxic to the plant unless the pot is regularly leached?

Basically it comes down to whatever works for you. If your plants grow OK with higher nitrogen fertilisers there is no problem, but avoid lush over fast growth from excess nitrogen fertilisation as cacti by nature are slow growing plants, therefore fast growth often comes at the expense of flowers.