How would you design an experiment to identify the most drought-tolerant grass from four grass seed samples?
What should the responding variable be? The height? Don't different grass grow a different maximum lengths?
A sketch of a procedure would be really nice 
Thank you soooo much! You're the best!!! 
the gut response is to grow all four with not much water and see which gets bigger - but you very rightly note that some grasses are just bigger naturally, nice one. that's a scientist's instinct that is!
what you need is a 'control' - a case where you don't put your samples under experimental conditions, to see what the default state is. so you would need to grow each plant under dry conditions, and also grow another sample of each under normal conditions with adequate water. by measuring the *difference* between the normal and dry plant of each sample, rather than the absolute height, you'll find out which is more tolerant.
in total you will have 8 plants - one of each sample in each of the two test conditions (dry vs normal) make sure you use the same amount of water on all the dry plants, and the same for all the normal ones. making sure you have controlled for 'confounding variables' (things influencing your plants apart from the amount of water), for example: all in the same amount of sunlight/planted at the same depth/in the same soil/pots/blahblahblahetcetcetc... this will get you uber bonus points in your write-up
it might be worth making a few brief qualitative (descriptive) observations as well as quantitative (measuring) ones - for example, which plants lose the colour in their foliage most? or go more brittle? etc. this might help to back up your measurements and conclusions (but remember - science likes the numbers best 
).
good luck!
 |
 75+ PERENNIAL WILDFLOWER GARDEN SEEDS FLAX BLUE DROUGHT TOLERANT $1.99 Time Remaining: 18d 33m Buy It Now for only: $1.99 Buy It Now |
 4 STOKES PURPLE ASTERS PERENNIAL DROUGHT TOLERANT DEER RESISTANT $4.00 Time Remaining: 12h 25m |
 5 SWAMP SUNFLOWER PLANTS PERENNIAL DROUGHT TOLERANT THRIVES ON NEGLECT $4.00 (1 Bid) Time Remaining: 12h 24m |
 Blanket Flower DROUGHT TOLERANT 333 seeds GroCo $1.00 Time Remaining: 25d 8h 25m Buy It Now for only: $1.00 Buy It Now |
 3 Lavender Munstead lavendula Perennial plants Sun drought tolerant butterflies $10.49 Time Remaining: 2d 14h 27m Buy It Now for only: $12.00 Buy It Now |
 Blue Yucca Drought tolerant Zones 3 8 xerascaping full sun $10.00 Time Remaining: 5d 8h 58m Buy It Now for only: $10.00 Buy It Now |
 Pretty AND Hardy ICE PLANT 3 lb Cuttings Delosperma FLOWERS DROUGHT Tolerant $14.00 Time Remaining: 17h Buy It Now for only: $20.00 Buy It Now |
 Shasta daisy live plant perennial sun summer bloomer drought tolerant $5.00 Time Remaining: 1d Buy It Now for only: $7.00 Buy It Now |
 Mexican Sunflower Tithonia rotundifolia 30 Seeds 4 6 ft Tall DROUGHT TOLERANT $0.99 Time Remaining: 20d 14h 12m Buy It Now for only: $0.99 Buy It Now |
 Shasta daisy live plant perennial sun summer bloomer drought tolerant $5.00 Time Remaining: 1d 5m Buy It Now for only: $7.00 Buy It Now |
 30+GAZANIA NEW DAY MIX FLOWER SEEDS DROUGHT TOLERANT GROUND COVER $3.89 Time Remaining: 17d 17h 43m Buy It Now for only: $3.89 Buy It Now |
 Maraschino Cherry Salvia sage 6 plants Drought tolerant attract hummingbirds $19.99 (1 Bid) Time Remaining: 17h 10m |
 Hot Lips Salvia 6 live plants drought tolerant attract hummingbirds $19.99 Time Remaining: 17h 6m |
 sedum NEON bright colorful flowers easy drought tolerant Live Potted Plant $7.99 Time Remaining: 8d 12h 51m Buy It Now for only: $7.99 Buy It Now |
 3 YELLOW ST JOHNS WORT PERENNIAL DROUGHT TOLERANT ALSO CAN BE A GROUNDCOVER $4.00 Time Remaining: 1d 10h 36m |
 flax scarlet DROUGHT TOLERANT 1000 seeds GroCo $1.00 Time Remaining: 9d 10h 17m Buy It Now for only: $1.00 Buy It Now |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $0.99 Time Remaining: 11h 6m |
 Gaillardia SeedsDrought Tolerant Brilliant ColorsCanadian Heirloom50+ Seeds $0.99 Time Remaining: 11h 59m |
 Rasberry Royale Salvia sage drought tolerant blooming hummingbird plant $4.00 Time Remaining: 28d 7h 24m Buy It Now for only: $4.00 Buy It Now |
 Shasta daisy live plant perennial sun summer bloomer drought tolerant $5.00 Time Remaining: 3d 6m Buy It Now for only: $7.00 Buy It Now |
 100+ ANNUAL WILDFLOWER Garden Seed FIELD POPPY RED CORN DROUGHT TOLERANT $1.99 Time Remaining: 18d 33m Buy It Now for only: $1.99 Buy It Now |
 Mexican Bush Sage drought tolerant abundant blooms dries well 3 live plants $7.99 Time Remaining: 17h 18m |
 3 Salvia Blue Queen Perennial plants Sun drought tolerant $10.49 Time Remaining: 2d 12h 45m Buy It Now for only: $12.00 Buy It Now |
 Heirloom New Zealand Spinach 50 Seeds Heat Loving Drought Tolerant $1.09 Time Remaining: 26d 15h 39m Buy It Now for only: $1.09 Buy It Now |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $0.99 Time Remaining: 23h 24m |
 Mexican Bush Sage drought tolerant blooms profusely late summer fall $4.00 Time Remaining: 27d 13h 23m Buy It Now for only: $4.00 Buy It Now |
 encephalartos manikensis 4in caudex cycad cactus succulent drought tolerant rare $99.99 Time Remaining: 3d 8h 26m |
 Zinnia Seeds Orange King California Giant Drought Tolerant 20+ Seeds $0.99 Time Remaining: 11h 6m |
 Queen Annes Lace Elegant White Lacey Flowers Drought Tolerant 50+ Seeds $1.99 Time Remaining: 2h 33m Buy It Now for only: $1.99 Buy It Now |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $0.99 Time Remaining: 1d 9h 36m |
 yucca RED YUCCA drought tolerant 10 seeds GroCo $1.00 Time Remaining: 24d 16h 3m Buy It Now for only: $1.00 Buy It Now |
 Gaillardia SeedsDrought Tolerant Brilliant ColorsCanadian Heirloom50+ Seeds $0.99 Time Remaining: 1d 9h 36m |
 Zinnia Seeds Orange King California Giant Drought Tolerant 20+ Seeds $0.99 Time Remaining: 23h 24m |
 San Marcos Festival Salvia sage Drought tolerant attract hummingbirds $4.00 Time Remaining: 19d 17h 14m Buy It Now for only: $4.00 Buy It Now |
 Mexican Evening Primrose Pink Flower 2 Starter Plants Drought Tolerant $5.95 Time Remaining: 3d 18h 13m Buy It Now for only: $9.95 Buy It Now |
 PHLOMIS FRUTICOSA JERUSALEM SAGE DROUGHT TOLERANT STARTER PLANT $3.50 Time Remaining: 22d 14h 32m Buy It Now for only: $3.50 Buy It Now |
 2 DWARF AGAVE Lophantha Plants DROUGHTHeat Cold Tolerant Evergreen Succulent $18.00 Time Remaining: 17h 2m Buy It Now for only: $26.00 Buy It Now |
 Zinnia Seeds Orange King California Giant Drought Tolerant 20+ Seeds $0.99 Time Remaining: 1d 15h 38m |
 Liatris Seeds White Strongly Drought Tolerant Very Unique 25+ Seeds $1.99 Time Remaining: 1d 4h 42m Buy It Now for only: $1.99 Buy It Now |
 YARROW RED PERENNIALDROUGHT TOLERANT EASY TO GROW 30 FLOWER SEEDS $0.85 Time Remaining: 1d 8h 15m Buy It Now for only: $1.00 Buy It Now |
 Zinnia Seeds Candy Cane Variety Deer Resistant Drought Tolerant 25+ Seeds $1.99 Time Remaining: 19d 13h 23m Buy It Now for only: $1.99 Buy It Now |
 Golden YarrowAbundant and Widespread Perennial ShrubDrought Tolerant50+ Seeds $0.99 Time Remaining: 1d 9h 36m |
 Mexican Bush Sage drought tolerant abundant blooms dries well 6 live plants $17.99 Time Remaining: 2d 16h 34m |
 Maraschino Cherry Salvia sage Drought tolerant attract hummingbirds $4.00 Time Remaining: 13d 16h 17m Buy It Now for only: $4.00 Buy It Now |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $0.99 Time Remaining: 2d 23h 26m |
 globe gilia DROUGHT TOLERANT 1000 seeds GroCo $1.00 Time Remaining: 4d 20h 23m Buy It Now for only: $1.00 Buy It Now |
 Gaillardia SeedsDrought Tolerant Brilliant ColorsCanadian Heirloom50+ Seeds $0.99 Time Remaining: 3d 10h 54m |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $0.99 Time Remaining: 3d 10h 54m |
 Gaillardia SeedsDrought Tolerant Brilliant ColorsButterfly Heirloom50 Seeds $1.99 Time Remaining: 19d 12h 32m Buy It Now for only: $1.99 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 23h 24m |
 75+ ANNUAL WILDFLOWER GARDEN SEEDS POPPY CARMINE KING DROUGHT TOLERANT $1.99 Time Remaining: 18d 33m Buy It Now for only: $1.99 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 23h 24m |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 23h 24m |
 May Night Meadow Sage salvia sylvestris Drought tolerant butterfly plant $4.00 Time Remaining: 20d 7h 14m Buy It Now for only: $4.00 Buy It Now |
 Dwaft AGAVE Lophantha DROUGHT Heat Cold Tolerant Evergreen Succulent STURDY $10.00 Time Remaining: 17h 1m Buy It Now for only: $15.00 Buy It Now |
 TORCH LILY Tritoma kniphofia desert easy 15 seeds drought tolerant $1.99 Time Remaining: 27d 19h 52m Buy It Now for only: $1.99 Buy It Now |
 Zinnia Seeds Orange King California Giant Drought Tolerant 20+ Seeds $0.99 Time Remaining: 2d 23h 26m |
 DWARF SUCCULENTAgave Lophantha DROUGHT Heat Cold Tolerant EvergreenFREE Ship $12.00 Time Remaining: 3d 19h 6m Buy It Now for only: $15.00 Buy It Now |
 sedum AUTUMN CHARM variegated sharp drought tolerant 1 QT Potted Plant $12.99 Time Remaining: 8d 12h 57m Buy It Now for only: $12.99 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Billy Buttons 50 Seeds Perennial Drought Frost Tolerant Groundcover Native $2.96 Time Remaining: 4d 21h 5m Buy It Now for only: $2.96 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Common Caper Seed Edible Fruit Buds Hardy Small Shrub Drought Tolerant $2.96 Time Remaining: 29d 23h 59m Buy It Now for only: $2.96 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Desert Yam Seed Bush Tucker Long Lived Perennial Drought Tolerant Evergreen $3.45 Time Remaining: 19d 23h 41m Buy It Now for only: $3.45 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 9h 36m |
 Dark Dancer Salvia sage drought tolerant blooming hummingbird plant $4.00 Time Remaining: 28d 8h 8m Buy It Now for only: $4.00 Buy It Now |
 Mexican Bush Sage drought tolerant abundant blooms dries well 3 live plants $7.99 Time Remaining: 5d 17h 25m |
 Queen Annes Lace Elegant White Lacey Flowers Drought Tolerant 50+ Seeds $1.99 Time Remaining: 15d 58m Buy It Now for only: $1.99 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 15h 38m |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 15h 38m |
 Poppy Seeds California Orange Drought Tolerant 2012 theseedhouse50+ Seeds $1.99 Time Remaining: 29d 6h 2m Buy It Now for only: $1.99 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 15h 38m |
 Australian Red Cedar Seed Drought Frost Tolerant Tall Rainforest Tree $2.96 Time Remaining: 16d 21m Buy It Now for only: $2.96 Buy It Now |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 15h 38m |
 Mexican Hat Seeds Prairie Coneflower Drought Tolerant 50+ Flower Seeds $0.99 Time Remaining: 1d 15h 38m |
 Gaillardia SeedsDrought Tolerant Brilliant ColorsCanadian Heirloom50+ Seeds $1.99 Time Remaining: 25d 4h 24m Buy It Now for only: $1.99 Buy It Now |
 Zinnia Seeds Orange King California Giant Drought Tolerant 20+ Seeds $0.99 Time Remaining: 3d 15h 52m |
 Gardening the Mediterranean Way: How to Create a Waterwise, Drought-Tolerant Garden List Price: Sale Price: $22.03 You save: $12.97 (37%)  Eligible for free shipping!Availability: Usually ships in 24 hours See Reviews For This Product DescriptionOver the last 25 years, Heidi Gildemeister has converted a dry landscape on the western Mediterranean coast into a gorgeous, thriving ten-acre garden. Her own experience and research have taught her the secrets of utilizing drought-resistant plants and waterwise gardening practices to allow the soil and plants to absorb enough winter rain so they can survive the dry summer...  |
 Scotts 18208 Turf Builder Heat-Tolerant Blue Grass Seed Mix, 20-Pound Sale Price: $49.99 Eligible for free shipping!Availability: Usually ships in 24 hours See Reviews For This Product DescriptionScotts Turf Builder Grass Seed contains our exclusive WaterSmart coating that absorbs 100-percent more water than uncoated seed and keeps it moist twice as long to help prevent it from drying out - even if you miss a day of watering. |
 Contrary Mary List Price: See Reviews For This Product Description"In Which Rose-Leaves and Old Slippers Speed a Happy Pair; and in Which Sweet and Twenty Speaks a New and Modern Language, and Gives a Reason for Renting a Gentleman''s Library. " |
 Garden Travels Alpine Garden Drought tolerant perennials Sale Price: $11.96 Eligible for free shipping!Availability: Usually ships in 1-2 business days See Reviews For This Product |
 Garden Travels Alpine Garden Drought tolerant perennials Sale Price: $14.95 Eligible for free shipping!Availability: Usually ships in 24 hours See Reviews For This Product DescriptionDave gets a Rocky Mountain High as he Travels to Vail for a unique Alpine Garden; Colorful Drought Tolerant Perennials in beautiful Santa Fe, at High Country Gardens.This product is manufactured on demand using DVD-R recordable media... |
 Scotts 18202 Turf Builder Heat Tolerant Bluegrass Seed 7-Pound Bag Sale Price: $34.99 Eligible for free shipping!Availability: Usually ships in 1 to 2 days See Reviews For This Product DescriptionContains Scotts exclusive Thermal Blue Kentucky Bluegrass. Grows 33% thicker per sq ft than ordinary tall fescue. Stays green even in scorching heat & drought. Aggressively spreads to repair thin and bare spots... |
 Drought Resistant Planting List Price: Sale Price: $22.47 You save: $12.53 (36%) Eligible for free shipping!Availability: Usually ships in 24 hours See Reviews For This Product DescriptionThe author of several gardening classics, including The Dry Garden and The Damp Garden, British horticulturist Beth Chatto has once again documented her gardening adventures in Beth Chatto's Gravel Garden... |
 California Patch Grass Seed- Drought tolerant, fast growing lawn repair for SW lawns. Sale Price: $9.99 Eligible for free shipping!Availability: Usually ships in 1-2 business days See Reviews For This Product DescriptionThis drought tolerant mixture of fescue adn rye will persist in your tough environment. Designed for fall and winter season overseeding or to persist in the cooler months our premier seed mixture is just right for your California lifestyle or Southwestern climate... |
 50 Pounds of Elite Grass Seed. For Full Sun or Shade, Drought Tolerant, Covers 7000 Square Feet. Sale Price: $78.00 Eligible for free shipping!Availability: Usually ships in 1-2 business days See Reviews For This Product DescriptionThis comprehensive mixture of both Perennial Ryegrass and Fine Fescue will have your new or existing lawn looking like the local Golf Course. Easy to establish and mantain this mixture will do the trick... |
