DTM days to maturity inaccuracy

ensete2002

11 years ago

i was researching dtm for melon varieties in order to decide on a sowing date. i have grown tomatoes for years, and my dtm always seem to take longer than the catalog says, except for cherry types. i have attributed that to my other than optimum conditions, and that i dont prune [sucker] my plants.
well, on a new mexico blog http://nmfruitgrowers.wordpress.com/category/melons/, someone said:
Myth #6 Follow the days to maturity guide in the catalog.
As a relative guide they seem pretty accurate, but the actual days to maturity was 20-25% longer than published.
they figured it was their climate's problems.
well today, i found
http://ucanr.edu/sites/sacmg/Melon_Demonstration/
which is from sacramento, california.
on the chart in the article, they listed the official dtm from the catalog. but in each description they noted the actual dtm in their test garden:
The seed packet indicated that melons are ready to harvest in about 84 days from sowing (our first harvest was in 92 days).
Ready to harvest in about 75 days from sowing (although our first harvest took 89 days)
Ready to harvest in about 75-85 days from sowing (ours took 106 days before the first melon was harvested).
Ready to harvest in about 90 days from sowing (this estimate was way off, as our first harvest took 145 days). [by the way, that is 61% longer!]
now this is in sacramento, which is a prime agricultural area
Sacramento has been noted as being the sunniest location on the planet for four months of the year, from June through September. It also holds the distinction as the sunniest month, in terms of percent possible sunshine, of any location in the world; July in Sacramento averages 14 hours and 12 minutes of sunshine per day, amounting to approximately 98% of possible sunshine.
in fact, california's central valley produces 90% of summer-harvested cantaloupes in the U.S.
so the sacramento area should be optimal for melon growing
if Sacramento's actual dtms are so much longer than the catalog ones, where ARE the catalogs getting those dtm numbers from?
in addition to being misleading, and possibly causing incorrect sowing timing decisions, i think it makes some gardeners feel they are doing something wrong.
by the way, i have the opposite experience with growing seedlings indoors. i use a 4 light fixture and grow very sturdy seedlings much faster than the time usually listed: that photo is of a 7 week old tomato seedling in an 1801 pot [3 1/8" square]. really, it was big enough to plant at 5 weeks, but the weather was still too cold.

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Comments (7)

planatus
11 years ago
An important variable is which side of the summer solstice the juvenile period falls upon. Many plants that are actively growing in May and June, when days are lengthening rapidly, will outpace the DTM ratings if they get plenty of sun. Late summer plantings will run 20 days behind, sometimes more. I would add two weeks to melons, especially if you delay planting to avoid first emergence squash bugs.

Interesting observations from the Sacramento demo garden. Bulb fennel and kolhrabi are always slow for me, but potatoes and lettuce are fast. Sweet corn is usually on schedule to the day. Go figure.
farmerdill
11 years ago
Here the published DTM for watermelons and canteloupes is pretty accurate as long the seeding times are optimal. An early planting is slower and frequently a later planting will catch up and be harvested at the same time ( July). Plantings for scheduled harvest in September take much longer due to day shortening

Here is a link that might be useful: dill's melons
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Days to Maturity
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I strongly encourage you NOT to focus on DTM overly much at it is at best a very general guideline that has little real value in common practice. DTM is determined by the average (not median) number of days it takes the particular crop to mature in optimal conditions in the zone where the test crops are grown by the seed producers for a particular seed distributor. This is why you see different DTM on seed packets bought from different distributors. Since so many of the seed distributors in the US now obtain many of their seeds from overseas the DTM they publish are not really applicable to the US gardeners. That said, DTM for vegetables normally grown from transplants is from the day they are transplanted to their final growing place. DTM is not size related and means nothing if they are direct seeded. DTM for vegetables normally direct seeded is from the day the seeds are planted in what will be their growing place and means nothing for those same seeds started indoors and later transplanted. DTM for all vegetables is only determined by what is the standard practice for sowing them. We can't have it both ways. No big deal since it means so little anyway. But what does days to maturity mean for those vegetables that are done both ways (lettuce for one) and is there a standard list of vegetables that are transplanted/direct sown? There are very few, if any, vegetables that have a standard practice of "doing it both ways" so no published DTM for them. Lettuce has a direct seeded standard practice attached to it. So the DTM one finds for them will always be based on that standard. You can 'estimate' a DTM by adding the number of days it took to germinate it inside to the DTM on the package and add approx. 2 weeks since that is the amount of set-back transplanting causes. But doing so makes the end info even less accurate. Now factor in the fact that few gardeners have or provide "optimal conditions" and that the BIG variable - weather -varies drastically from zone to zone and even within zones and you begin to see the problem. Yes there are many lists but how accurate can they be since they just use standard practice. And even they are zone specific as what is 60 days for lettuce in southern CA is more likely 70-75 days for the same lettuce in say Idaho. So what is the solution? Detailed record keeping for a couple of years in your own garden. Note the day you direct seed some lettuce inside to be transplanted and the same lettuce outside, the date it germinates both places, the date it matures from both plantings. Then you have your DTM for that lettuce variety IF the weather cooperates from year to year. Hope this helps even though it likely isn't what you want to hear. Dave
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I'm not at all sure why you would consider any of my response condescending. I just asked a couple of questions, primarily because I know you are located in the PNW as well. Zone 8 in the PNW (including BC) shares an extremely similar marine climate......as well as a similar growing season. With just a few minor adjustments. Typically, this will be from April through October - maybe slightly earlier in some specific locations and slightly later into the fall in others. That's right around 7 months, a pretty decent length of time for most annuals and not at all what most consider to be a "short" growing season. Short is most of Alaska, at 3 months or less. The only issue that really restricts planting time here is heat (not frost). While we may very well not experience any frosts during that period, it also doesn't get very warm.....and the soils take a long time to warm up in spring. Hot season plants are sometimes slow to come on unless started in advance indoors and grown on until things warm up enough to transition them outside. If sharing my experience and familiarity with the climate and location is condescending, then so be it. Sorry.
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Ahhhhh! The age old 60 million dollar question! When I was a youngster, it was the 60 thousand dollar question. But with inflation and the recent slump of the US dollar against world currency, it has become the 60 million dollar question. The real answer is CUMILATIVE GROWING DEGREE DAYS. If you add them up from the transplant date to maturity, it will be right on year to year. Trouble is, year to year, the total will vary say from May 15th to July 15th. Therefore the maturity date will vary.
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Yes, Albert, that was my point. If you want to get to harvest fast, get a plant that has a smaller DTM. That is, a longer DTM plant planted next to a shorter DTM plant wlll probably take longer to produce. But if you want tomatoes on July 15, and you have a plant with a DTM of 90 days, planting on April 15 may or may not do it for you. Given variability of weather, climate, and planting dates, as well as soil nutrients, you decide when to harvest by looking at the stuff and seeing if it is ready to harvest. Not by when the calendar and the DTM tells you it is ready to harvest. So calendar-wise, DTM is indeed a pretty useless bit of information.
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sunnibel7 Md 7
11 years ago
I always rather thought they based dtm on growing out the seeds themselves and recording average dtm. And I figured that since my conditions are not exactly the same as anywhere else, the dtm is just a guideline. And since the weather can vary so much from year to year, how could I expect the same dtm from the same seed in a cold, wet spring versus a warm, mild spring?

I do use it to make decisions: if I want to have a long corn harvest and to only sow the seed once, then I get 2-3 different cultivars with different dtm. If I were picking from the Johnnys catalog I'd probably go with Spring Treat at 66 dtm, Lucious at 75 dtm, and Silver Queen at 91 dtm. Even if the the actual dtm varies from what is stated, they will all be growing in the same conditions and have roughly the same spacing in harvests as indicated by the catalog's dtm.

I think the trouble lies in the expectations of new gardeners for things to be hard and fast and quantifiable... Like expecting dtm to be exact, watering to happen on a strict schedule and to provide an unwavering amount, hours of light for seedlings to be set in stone (regardless of the type of fixture used), how many of each plant to provide enough food for a person...
digdirt2
11 years ago
Agree with weirdtrev. This has been discussed here frequently - that DTM has never been anything more than a general guideline and not something to base gardening decisions on.

There are far too many variables that affect it for it to be considered anything more than an average, an estimate.

Dave
veggiecanner
11 years ago
It would help if they were more closer for planning fall plantings. I used to plan the whole years garden in the sping but now I wait till summer to plan the fall garden cause the summers harvests were not even close to what it said on the pkg.
edweather USDA 9a, HZ 9, Sunset 28
11 years ago
Since we grow in containers things tend to grow a little faster than in the ground, and last year we found that the DTM for watermelons was very accurate. This is particularly helpful due to the difficulty in judging watermelon ripeness, especially when you only have a few and don't want to waste any "test" melons.

DTM days to maturity inaccuracy

Comments (7)

planatus

farmerdill

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sunnibel7 Md 7

digdirt2

veggiecanner

edweather USDA 9a, HZ 9, Sunset 28

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