soil warming

[Dave Brown]

Blimey Greville I thought I kept some records, but not nearly as detailed as yours. The only palm I now keep records of is the Washingtonia.

Did you keep any record of the actual soil temperature I am finding that raising a clay soil temp is difficult as the water tends to spread out rather than go in where you pour it. Also the volume makes it quite expensive if heating with electricity or gas, that is why I have the 300 ltr paddling pool.

What volume of water do you use on ground planted palms I found about 30 ltr of 30C raised the temps by 2 C from 8 to 10C at 30cm depth in March, and this lasted a couple of days. The Washingtonia actually starts to grow with a soil temp of 8C with air temps above 13C, and this is why it does so well at recovering from winter damage.

I did growth trials last year trying to relate soil and air temp to growth rate, but measuring petiole growth was not reliable, as they seem to grow at differing rates depending on part of the growth cycle, significantly slowing down as the petiole got longer. Eventually I decided a better method of measuring was the days between the fan starting to open. However as this was only adopted in June I don't have a full year reading. I will use this method this year.

The first fan this year started to open on 14th Feb, with a 30cm soil temp of 8C. With max weatherstation temps of 9 to 13C the 10 days before. However it is warmer in the sheltered corner where the palm is.

[GREVILLE]

Two other exotics that have been given warm water in my shady NW facing house border are Dicksonia Antartica and Arundo donax variegata.

The Dicksonia antarctica simply gets warm water drenched in the crown every time the palms are treated. I've never protected this overwinter and any knuckles present quickly unfurl in the spring. I have given plain cold water other times but I'm not convinced that higher temperatures provide any advantages as much the roots are above ground and will respond to any current temperature and humidity.

Arundo donax var. is a differrent matter.
I planted one in 1991 at the top end of my NW border where it gets afternoon sun earlier than any thing else there. It always started late with the first new shoots appearing around the end of May to join any old shoots left in situ after winter.
In April 1995 I included this with my warm watering treatments and two new shoots appeared before the end of the month. By the end of May both shoots were already four feet tall - a huge gain on the same period in previous years.
An identical result occurred in 1996 but alas nothing in 1997 as it perished in frozen wet soil.

I put another one in the same spot in 2006 and gave warm water to establish it and it responded with three more new shoots later that summer. This new one was treated with warm water and full strength liquid feed weekly April to July for the next two years and I had an impressive plant double in size over my previous one. It never regrew after the freeze of 2009-10. This one definitely likes the hot tub and not the ice plunge!
My next one will be lifted every winter and restarted with warm water in the greenhouse.

[RogerBacardy]

Thanks for all the great posts in this thread.

Had never occurred to me that cold hosepipe water in mid summer could lower soil temperatures and slow down growth rates.

I have 3 waterbutts and the good thing about those is that the water can get pretty warm on sunny days, due to the sunlight warming up the dark plastic.

[GREVILLE]

Dave, I'm sure you're right about the difficulties of warming clay soils especially on a flat level or worse still a sump. Although I have heavy yellow plasticine clay sub-soil it is very deep, especially where I have built up raised beds as much as a metre with my large rockery. With such good and deep drainage I am confident that my warm water goes exactly where I want it without splashing out on too much.

I recorded details of two crude soil warming experiments in the mid-nineties which gave an idea of how much warmth is kept in the soil early in the season.

In 1995 March was cold but early April saw the start of a particularly warm spell which coincided with the beginning of my warm water escapades for this year and before starting I took the following temperature details:
Third day of warm spell.
Air temperature 19c Soil temperature upper end of shady
NW facing house border
3cm depth 12c
15cm depth 8c
surface temperature (in shade) 15c

Warm water(35c) added and temperatures taken 4 hours later.

Air temperature 20c (5PM) Area now in sunshine
3cm depth 18c
15cm depth 13c
surface temperature (in sun) 23c

Two days later with dry mild weather continuing the following readings in the same place are:
Air temperature 17c 3cm depth 15c
15cm depth 12c
Surface temperature (shade) 15c

The most significant figure here must be that after two days the soil temperature at this shady spot is still 4c warmer at 15cm. This from one application of a full watering can (10 Litres) The area watered had no plants or roots and measured 50cm x 50cm
I think the relatively high day time temperatures contributed to this.

The same tests to a warm sunny and sheltered spot half an hour later produced the following results:

Site: A raised bed against south west facing house wall which has a warm microclimate.

Air temperature 22c (Thermometer shaded from sun)

Before watering - soil depth 3cm 18c
15cm 15c
surface temperature 26c

4hours after water - soil depth 3cm 20c
15cm 18c
surface temp 23c

(I didn't log the air temperature at this time)

Two years later I carried out near identical experiments in the same places at the beginning of April 1997.
For the shady border I put in 20 litres of 35c water. After a cold winter but warm spring I started with an air temperature of 14c but with the same readings about 1c lower across the board. As it was a cloudy day the surface temperatures were the same as the air.

In the sheltered SW house bed, I did an extra test with soil temperatures in the root run of an established Washingtonia.
Here the readings came out as follows:

Unplanted spot (same as two years before)
Air temperature 15c 3cm depth 14c
15cm depth 12c
surface 16c

Washingtonia 3cm depth 15c
15cm depth 13c

After warm watering 4hours later:
Air temperature 14c unplanted spot 3cm depth 15c
15cm depth 15c

Washingtonia 3cm depth 16c
15cm depth 18c
Two days later in slightly warmer weather only the 15cm depth of soil in the root run of the Washy had dropped by one degree - all other figures were unchanged.

I also did an identical test the same day in the root run of a Phoenix canariensis_CIDP in another part of the garden and got exactly the same readings. If it seems that soil holds heat well then planted soil does even better.

With this hot water approach the aim is not only to start plants moving early but to maximise the amount of growth made in a season. To that end I tie some white twine to the newest open palm leaf at the end of the year and do another one the following year counting the open leaves made in between.

I'll put on more information from the results on other plants on more posts and finish with my conclusions on the benefits of warm watering.

[GREVILLE]

I'll list below the growth results to the palms grown on the warmest bed. This is the same SW facing house bed that had the temperature test.

Washingtonia Filifera.
6 month old seedling brought back from California 1991. Planted out 1993. 5 leaves and a spear into mild winter. Repeated 1994.

Results from soil warming treatments:
1995 - 8 leaves and 1 spear.
1996 - 9 leaves and 1 spear (still growing into 1997)
1997 - Cold water monthly this year. 5 leaves, 1 spear.
1998 - Warm water and feed. 11 leaves, 1 spear.
1999 - Cold water monthly. 7 leaves, 1 spear.
2000 - Warm water and feed 12 leaves, 1 spear.
2001 - Spear opens fully before winter is out and warm water treatment gives 14 leaves to the end of 2001

Subsequent years saw some very invasive root competition from other fast growing exotics reduce the number of leaves to 10 and below annually. Also the leaf sizes reduced somewhat. In 2006 the Washingtonia was given no water and feed at all, surviving on scant summer rains and only produced 5 much smaller leaves. I went to the other extreme and gave this hot water from the hose three times a week all spring and summer 2007 along with weekly doses of soluble Ammonium Nitrate. It took this much extravagent treatment to overide the heavy competition of greedy neighbours and was rewarded with 12 much larger leaves to the end of the year.

This year I started some warm water treatment during the mild February we had. Unfortunately, this was an act of desperation as I was trying to kick start some growth having cut back more than a foot of trunk after winter damage. This palm has actually continued to grow slowly in some mild winters but not any more It seems well and truly dead and I think I'll be starting all over again with a Filibusta

My three heat loving slow growers up next.

[GREVILLE]

This SW facing house bed is certainly the only spot in my garden to get any growth out of Sabals minor and palmetto and Syagrus romanzoffiana.

Sabal minor - purchased as a young plant in 5 litre pot with two adult leaves in 1996. Kept in greenhouse till planted out in Spring 1998. Managed one leaf and a spear in 1997.

1998: Warm water weekly till June thereafter twice weekly. No feed
One leaf and one spear
1999: Cold water with weekly liquid feed half strength
Spear from previous year finally opens in August
2000: Warm water and feed. Two leaves one spear
2001; Warm water and feed. Two leaves and one spear.

After just a single leaf in 2002 the fierce heat of 2003 produced its best result. With frequent applications of warm water three full leaves opened, two of these opening in August and September.

Thereafter it was crowded by other plants above and below and barely managed a leaf a year, In 2009 the spear failed to open and the plant perished the following winter.

Sabal palmetto: Purchased 1996 as a chunky plant in 10litre pot and planted out in 1997.

1997: Cold watering only. Spear opens August.
1998: Warm water and feed. Two leaves one spear
1999: Cold water and weekly liquid feed. One leaf one spear.
2000: Warm water and feed. Two leaves and one spear
2001: warm water and feed. Three leaves one spear.

In 2003 I managed an almost open 4th leaf by September after the hot weather. Two or three leaves per year are regular results to date'

Syagrus romanzoffiana - Purchased a seven foot specimen in1997 and planted July. No new growth this year

1998: Warmed rainwater from greenhouse butt.
Spear opened August, one small spear followed.
1999: Cold water and feed with ericaceous fertiliser.
One leaf and one spear.
2000: Warmed rainwater and feed monthly. Two leaves and one spear.
2001: Warm Tap water (hotter than greenhouse water) and feed
Three leaves and one spear.

This palm was given rain water as I understood it had a liking for acid soil. The water was not as hot as the tap water but in 2001 I used 40c tap water with a chelated feed and got better results.

In 2002 my Acacia rhetinodes blew down in a storm and crushed the Syagrus.

[kata]

Awe,

Soz about the Acacia Grevillie.

If this is a lot of work its my favourite gardening pastime. I am bonding with my beauties as they lap up this loving treatment. It's like sharing a warm bath with your loved one

Nothing wrong with that., My BIL talks to his plants, says I don't talk to mine enough when ever I have a problem

Intersting posts.

[Dave Brown]

Trying to kick start my Washingtonia as it has suffered so much this winter. Watered 22.5 litre of 35C water Raised 10cm from 6 to 14C over 2 hours. 30cm depth raised from 8C to 12C.

[Mr List]

how do you get the water to the right temperature?

[Axel]

Very inspiring post Greville. I gave my palms a good soaking yesterday with 35C water. I have a large chamaerops (1.70 meter trunk), nearly defoliated, that i hope to kickstart with warm water. Thanks.

[Dave Brown]

how do you get the water to the right temperature?

35C is warm to the skin, unless you have been working in freezing conditions in which case 20C can feel warm. 40C is bath temp. I have an aquarium thermometer with a waterproof probe, which I can use to check if needed

I use mixer taps into a watering can, but would love to rig up an electric shower running on the cooler settings.

Of course soil heating cables would achieve the same thing, Warming the soil, but thermostats are not cheap if you have multiples in the garden.

[Arlon Tishmarsh]

How about hot and cold supply to the outside with a thermostatic mixer valve, an old shower valve would do ?

[Dave Brown]

That's a good idea Arlon, but my main problem is I am all electric, so the hot water is an immersion heater. I don't think a 3K immersion would heat it quick enough The water would run cold fairly quickly

[Arlon Tishmarsh]

Ah right, didn't know. Hence the electric shower

[Axel]

Greville, have you tried the warm water treatment on a Phoenix canariensis_CIDP as well? They are always very late to start growing, usually july/august (unless planted in a frostfree zone), so perhaps they can be speeded up considerably by warm water.