Dolomite does not have potassium in it, but magnesium...CaMg(CO3)2

I'm assuming you've had a professional soil test.
If not, I wouldn't add anything until then.
Are you near the coast and if so, can you get seaweed? It's full of all sorts of goodies, including k.

Yes, rhizo... you are right. I just did not remember it right. I was confused about Dolomite lime being rich in calcium but remembered it as being rich in potassium.

Thanks

Yes, I did have a soil test.

No..not near the coast at all.. hard to find seaweed. There are plenty dry seaweed in asian supermarkets where are not close either.

check ebay for a vendor named kelp4less. I have bought from him and is a satisfied customer. I have no other financial incentive otherwise.

Hope this helps.

Buying seaweed like that would be insanely expensive and me offering you advice from on the other side of the world will probably do you no good whatsoever!
That never stopped me before, so...
Glad you've had a soil test. Was everything else present in decent quantities? What's your ph?

just to let you know, I was composing as AMaji was posting: my comment was not regarding their recommendation.

Organic sources of Phosphorus can be somewhat difficult to find since many "garden centers" do not carry those low profit items and there are not that many. Rock and Colloidal Phosphate, Bone Meal, manures, and organic matter (compost, shredded leaves, etc.) are all sources, but what you might use will depend on what you can get fairly inexpensively.
Phosphorus levels in my soil have increased from low optimum to high optimum simply from the organic matter added over the years.

Kimm, the OP is asking about K.

One easy source of K is hardwood ash, which also is high in P, so it's best to add if soil needs both. Remember that if the exchange rate is low that P even if present in adequate amount is possibly bound up, a common situation in sandy soil. If the exchange rate is low then one needs a lot of OM in addition to some salt form of K like hardwood ash.

Greenwaste compost provides oodles of potassium.

Hey! What about granite dust from the hardware departments? It's used to make stone or brick patios and walkways. If you have a decent hardware store or hardware section of a big box store, you should be able to find bags of it for VERY little $$$.

The so-called stone dust for setting patio bricks is very coarse and will have a very tiny proportion of particles that are 200 mesh or finer, which is what is needed to be able to be broken down quickly by micro-organisms. If you look at ag lime that is how fine it needs to be.

If your soil test indicates a need for potassium, consider comfrey tea. Best if you have your own patch. Your area Freecycle could be a source if you do not have a local garden/herb club or two close by with annual plant sales. Easy to make. You might try contacting the USDA extension office in your county. Many have organic growers/advisors/master gardeners. There are regional reps for some organic suppliers, such as Fertrell. The best way to locate these, is to do a web search. When I lived in another state, a dealer was five miles away.

Will comfrey grown on ground low in K be a dense source of K?

How about liquid molasses? You can find it at almost any grocery store by the pancake syrup. It has ample potassium, along with calcium and iron. Plus it's great food for beneficial bacteria. Mix it 1TBS per gallon and water or spray plants, or both!
If you need a large amount for a big garden or farm, check your local feed store for dried molasses. It's used as a sweet feed for animals.I think I paid $15.00 for 50lbs.

Hmm. Wonder where my mind went the other day. Compost is a good source of Potassium and probably the easiest to get. Commercial sources such as Granite Meal, Greensand, Kelp Meal, and Sul-Po-Mag, if not available locally can get pretty expensive when shipping cost is included. Wood Ash is a source but is also a source of very large amounts of Calcium Carbonate. Molasses may be a source, but can get fairly expensive.
Green Waste compost is another name for compost made with not animal products, manure, blood meal, etc.

My oldest garden tested high in P and Ca, most likely from years of additions of wood-ash and urine-rich compost. K was quite low, since it is a nutrient that is very heavily drawn down by most crops and is not naturally abundant in sandy soil.

Buy a bag of potassium nitrate. Problems solved at low cost compared to some of the items mentioned. Of course any source you can get for free would be even cheaper. Free is good.
Some potassium and sodium nitrate still comes from caves full of bat guano or guano from islands inhabited by sea birds off Chile and Peru.

Nitrates are high-index salts that rapidly end up in the environment to bad effect and are entirely un-necessary in a properly managed system. I strongly suggest disregarding that last recommendation. Crop plants with high levels of nitrate resist insects and disease poorly and are unhealthy to eat, even though they may look lush and thriving. There are much better sources of K available.
High use of nitrates in the form of synthesized salts is a major part of what is wrong with commercial ag. It is also what is wrong with most organic operations where the nitrates and phosphates are pumped in through animal manures while the rest of the nutrients are allowed to decline along with plant health.

potassium nitrate is not an acceptable product for organic gardeners/farmers to use.