Teddahlia How big are bowls for floating waterlilies at shows? Can I use a popcorn bowl? 
Soil Test Questions
a month later
Teddahlia I brought my sample over to the co-op yesterday, so I should have results next week. Thank you for the reminder!
This may belong in another thread, but I recall you saying that a time-release osmocote type fertilizer is best for grow bags. I have about a dozen of those, which are excellent for spares and pot tubers and the inevitable “I forgot I ordered this tuber!” I’ve been mixing garden soil with last year’s grow bag contents, annd I’ll add some time release fertilizer. Anyone else have suggestions for how to provide a good growing medium in a bag?
Last year we were able to put tubers in by April 15. It feels like the right time to start now. Happy planting season, everyone!
Two pictures from last year’s grow bag area.
I believe the major concerns about the soil in grow bags(I am using our experience with growing dahlias in pots of 15 or 20 gallons but seldom smaller) are the weight of the soil and having healthy soil in the bag. The weight issue is applicable mostly if you plan to move the bags around. Potting soil mixes vary a bit in weight but all of them are lighter in weight than garden soil. The people who grew them on Dahlia Talk said they bought a load of 3 or 4 way soil mix and I believe the mix may be compost, top soil and sand and may have bark dust or some other filler. Anyway, it is probably lighter than garden soil but if it has sand in it, I take that back as sand really heavy. Ideally, the bags would be filled with expensive bagged potting mix but who has that kind of money? If one makes their own compost, it could be mixed with some garden soil and the result would be lighter and pretty healthy. We re-cycle old potting mix and sift it and use the old stuff on the bottom half of a pot. We have the same goal of keeping the pots light enough to be able to move them. 20 gallons of garden soil almost needs forklift to move. By the way, we use larger pots (15 or 20 gallon) for dahlias because of watering issues. They hold enough water so that the plants only need one watering per day. And we use osmocote type fertilizer as it is too easy to burn dahlias in pots using granular garden fertilizer. One of the big downsides to potted dahlias is the daily watering. Your garden is watered much less frequently and with our drip tape it takes almost no effort. 
HH Pink Martini has become much more popular in recent years.
Our solution for watering grow bags was to group them in a long line of clusters of 4 bags. We use the "Downward Sprinkler" from Dripworks...they are a little whirly springler-et that spins out a circle about 12" in diameter. Thus one sprinler placed in the middle of 4 bags will spin water into each bag. The downsprinklers can be placed anywhere along the drip-line. We watered about 74 growbags this way last year and it worked. I will use a better soil this year as last year's was too sandy and drained faster then I wanted. It was also a bit low in nutrients...our local sources idea of organic garden soil, which also introduced the new invaders, "Jumping worms". Our soil has been imported from Hillsboro, Oregon this time and looks very different, and passed the "Pea test".
Another issue about grow bags is staking up the flowers. How do people do that? Some of the Hollyhill varieties may possibly be too tall. 
- Edited
I wondered about that last year but those 15 gallon grow bags are so heavy nothing moved in the wind! I did line the grow bags up two by two with a mini sprinkler in the middle then a small gap before the next set of 4 on down the line. We put in the metal stakes at the 4 corners of the rectangle with twine around them just like for the raised beds, but I never saw any actually need it.
But I will do the same again, because those bags aren't moving...and the posts are still there.
5 days later
OK here are the results of my 2024 soil test. I added the numbers from last year's test where they differed significantly.
I'm disappointed that the pH has gone from 6.5 to 7.0. Anyone have ideas about that?
Last year, I had brand new soil that was high in almost everything. It was suggested that I test again after the season to see how things settled out. As advised, I did not add anything to the soil, but did do some foliar feeding from time to time, so I imagine that gets in there. I know one of them was a calcium supplement, but that value has gone down.
My plants did well in this soil last year. There were a few that were excessively bushy--too much foliage and very very few blooms. I wondered if there was some pocket of high nitrogen soil in that area. They were all together in a group--about 5 plants that had given me tons of flowers the previous year were gigantic leafy overgrown, and gave just a couple of blooms, if that.
Anyway, there's not a lot of time to make adjustments, but I would welcome any suggestions!
Thanks!!
Phosphorus is dangerously high so do not add more and do not add bone meal either. 6.5 pH is ideal for dahlias. 7.0 is a bit alkaline but that does help with the excess phosphorus. You only need to add nitrogen and do it evenly and not too much at one time. Organic material is high but not too high.
Teddahlia thank you. I was hoping that the phosphorus would come down, but I know that takes many years. I’ve never added anything with P in it, and I’ll be cautious about any amendment. The soil came pre-loaded with extra P, and lucky that I had the soil test last year, as well as the collective wisdom of this group!
Is organic material a concern at this level?
Also, what are safe ways to add some nitrogen without it being a) too rapid, and b) combined with Phosphorus?
- Edited
In the old days nitrogen was in the form of nitrates . It is nearly all urea based now. Nitrates burn plants. Urea added in recommended amounts does not. It also takes a week or two activate as it is converted to nitrates by soil bacteria. Use the soil test data to calculate how much to add per 1.000- square feet and spread the amount over a couple of months. If in doubt about how to calculate it, a teaspoon of 46-0-0 urea per dahlia plant and watered in will get them growing well and is not too much. I use sulfur coted urea as it is a time release product and lasts for 6-8 weeks when applied. And it adds my needed sulfur too . I would add twice as much as it is time release. Organic gardeners rely on blood meal, chicken feather meal and sometime bat guano for nitrogen. Manures may have some nitrogen but are overloaded with phosphorus. Fertilizer is a very complicated subject and there are more myths out there than accurate information. AND THE ORGANIC MATERIAL IS OK EVEN IF A BIT TOO MUCH.
JessieC I always add a small amount of alfalfa meal to my planting hole. During the season, I use a soil drench for my plants when they are still small and a foliar spray for later on in the season. I make up my mixture using Organic Neptune Harvest brand fish fertilizer and seaweed plant food (2 separate products). My dahlias seem to like this mixture.
As I read how people use various fertilizers and supplements and are organic or whatever I have noticed over the years, the ones who really, really grow the very best dahlias are the ones who do less fertilizer but more often. Most all of these exotic fish fertilizers and things like alfalfa meal or chicken feather meal or the strongest most powerful forms of chemical fertilizer work very well in small doses done often. Why does time release fertilizer work so well as it has the the same ingredients as the most powerful fertilizers? It is because plants want a little bit of fertilizer all the time, not all you can eat buffets once per month. I will always remember the fertilizer seminar done at Federation meeting where the very best exhibitors in the entire USA explained how they fertilized. The person who has proven to be the top show exhibitor of all, explained how she used cheap farm fertilizer in small doses and observed her plants carefully so she did not over fertilize or under fertilize. IF I WERE RICH and could use any fertilizer on the dahlias, I would either fertigate(fertilizer injected into the water in small amounts) and/or use the expensive osmocote type time release pellets., I would buy expensive equipment to measure the nitrogen in the dahlia leaves and have my crew with their pHDs keep track of the results of the fertilizer program. And a note on fish fertilizers and seaweed and such: Yes, they do have useful micro ingredients that your garden may be lacking. However, as with everything too much of a good thing is a bad thing and relying on these products as your main fertilizer year after year is probably not a good thing,
Teddahlia I have read your above article to the man who does the fertigation and watering system here. It was very useful. Thank you! Its always good when "the help" understands just what they are trying to accomplish!
My soil test results showed:
5.6 pH (I amended with some lime, just a bit)
6-13% organic matter
Very low Nitrogen
Med-High Phosphorus (weak bray)
Very Low Phosphorus (NaHCo)
Med Potassium, Calcium, Magnesium
No trace minerals
Besides the lime and a Nitrogen-rich fertilizer, 1 lb/1000 sq ft Phosphate was recommended. I have an ample supply of liquid duck pond water this year but haven't picked up a Phosphate amendment.
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"5.6 pH (I amended with some lime, just a bit)"
The pH of 5.6 is very acid and a bit of lime will not change it that much. If you do not add more lime it only means that you need a bit more fertilizer as acid pH inhibits the uptake of fertilizer.
I did get recommendations from the test provider (King County Conservation) on lime amendment rates for 5.6 pH and what I mean to say is I did not treat them with as much lime as suggested, presuming their rates for "flowers" were based on a more alkaline pH than dahlias prefer. It still may not have been enough and since my nitrogen is so low it does sound like a good idea to add more fertilizer.
JessieC I'm disappointed that the pH has gone from 6.5 to 7.0. Anyone have ideas about that?
Jessie, I had a similar soil report last year and had good results supplying the nitrogen with Ammonium Sulfate 21-0-0. The sulfur will also help in lowering your pH. I like it because it is cheap and dissolves completely in water so I can use it in my injector without plugging up the drip tape. If you get it at the big box store make sure it does not include a "weed-and-feed" ingredient that many of the lawn ferts have. You want only Ammonium Sulfate (21-0-0).
SteveM
Oh that is so helpful Steve. Thank you! I was about to ask “how do you find the fertilizer without added P?” And of course I wonder what will help the pH too.
I’ll look for that.
And Flowernut Thank you for that insight. I don’t know if I have seen alfalfa meal, but I think I’ve heard of it. Does it attract critters?
Teddahlia Most helpful, as always. Thank you!!
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You can get either Alfalfa pelllets or meal at any animal feed store....like a hardware store that also sells animal feed. The pellets are just ground alfalfa presed into pellets for ease of handling. Either one works fine. I just mix some into the dirt at the bottom of the hole before planting my tuber or plant. You could also dig it into the whole bed if you want. Or scatter it over the surface then rototill. I find it easier to add a scoop at the bottom of the planting hole and stir it up a little.
"You want only Ammonium Sulfate (21-0-0)"
This chemical is almost poison on acidic soils like ours. It is the most acidic of all the nitrogen fertilizers. If you have alkaline soil it is good. If your soil acidic it is bad. Cheap fertilizers that are sold here have it as an ingredient. It would be OK if you added the same weight in lime as you apply it.